3.0 Biology

Echinoderms live in marine habitats.

Another animal phylum you might recognize includes sea stars, sea urchins, sand dollars, and sea cucumbers. The animals in phylum Echinodermata (from the Latin terms for spiny skin) have hard outer skeletons. They also have a network of tubes in their body called a water vascular system. Echinoderms use this system to help them move. To explore the anatomy of an echinoderm, click Sea Star Anatomy Opens in modal popup window . Did you notice radial symmetry? Good observation—but, did you also notice that in the text on page 139 of your reference book that they have been grouped with the animals with bilateral symmetry? It turns out they are bilateral when they are larvae, and their bodies change to a radial shape as they mature.

People, fish, frogs, birds, and lizards are all vertebrates.

Arthropods are the most abundant animals on earth, but vertebrates are the animals you're most familiar with. Vertebrates are a subset of the animals in the phylum Chordata. Chordates are characterized by having a nerve cord that carries information between the brain and other parts of the body. Most chordates have an internal skeleton made of bone, cartilage, or both. In addition, chordates have a complete digestive system, and most have a closed circulatory system. Chordates include fish, amphibians, reptiles, birds, and mammals. There is extraordinary diversity in this group of animals. Review the basic anatomy of a representative chordate: Fish Anatomy Opens in modal popup window .

3.08 Three Representative Organisms Ferns, flatworms, and humans have common needs and share some basic characteristics, but they meet their needs in different ways. ferns, flatworms, and humans have biological needs met in different ways

As you learn about the diversity of life around you, think about the characteristics that the organisms on earth share and the characteristics that make them unique. Thinking about organisms in the context of how they meet their needs will help you understand the diversity in structures seen in organisms on earth.

Most plants do not have a digestive system because they do not take in external substances.

By and large, plants don't have a digestive system because they rely on sunlight and photosynthesis for energy. But there are several plants—including the Venus flytrap, pitcher plant, and sundew—that trap and digest small insects and animals for additional nourishment. With no digestive system, how are those plants able to digest the bodies of the insects they trap? The leaves of the Venus flytrap can snap shut over a small animal or insect. The leaves also produce digestive fluids that break down the organism's body. Those fluids—in this case, potassium and nitrogen compounds—are then absorbed back into the plant and distributed to its cells. Once a leaf opens again, the indigestible parts of the organism eventually fall out. A few plants, including Venus flytrap, have specialized structures that trap small organisms. Digestive fluids in the plants break down the organisms.

Taxonomy is the science of classification. Shows Plants classified into Nonvascular plants, ferns, gymnosperms, and angiosperms.

By establishing a consistent system for naming organisms, Linnaeus helped pave the way for the development of taxonomy Opens in modal popup window , which is the science of classification. Taxonomy helps organize all life on earth into categories based on patterns of evolutionary relationships. Observation has shown scientists that organisms that have many similarities share a more recent common ancestor than species that aren't as similar. Classifying an organism based on its similarities with other organisms, then, should reflect its evolutionary history, or phylogeny Opens in modal popup window . It turns out that taxonomy—the process of classifying and identifying organisms—arranges organisms into groups that really do reflect phylogenetic relationships, or relationships based on shared evolutionary histories.

An organism's scientific name consists of a genus and a specific epithet. Although quite different in appearance, all of the leaves and acorns here are from trees of the genus Quercus, the oaks. (shows pics of acorn varieties)

For example, many different types of trees belong to the genus Acer, which includes all maple trees. Acer saccharum is a tree that has the common name sugar maple. The sugar maple has leaves that turn bright red in the fall. Acer pennsylvanicum has the common name striped maple. As the common name suggests, it has striped bark. Linnaeus's two-part naming system, called binomial nomenclature, persists to this day. Scientists around the world use two-part names to refer to species. Because they all agree on the same naming convention, there's no confusion.

3.04 Viruses are nonliving particles that cause infection in many organisms.

Have you ever had chicken pox? How about the flu? Or the common cold? Each of these illnesses-and many others-is caused by a virus Opens in modal popup window . Viruses are nonliving particles that are made up of a protein coat surrounding a segment of either DNA or RNA. Viruses are not cells. They do not take in energy from the environment. They do not grow. They do not have a metabolism. They do, however, reproduce, but they can't do it alone. A virus injects its DNA or RNA into the cells of living organisms. The living cell then makes many new copies of the virus.

Like many other animals, humans are active and have many specialized systems.

Like flatworms, humans and other primates have systems that help them sense the environment. Humans must find food because they can't make it themselves. A human's body is far more complex than a flatworm's, and includes well-developed systems for digestion, respiration, waste removal, and other important functions. Unlike flatworms, humans can't rely on simple diffusion to provide oxygen to all body cells. Instead, they have a complex respiratory system that works with a cardiovascular system to bring oxygen into the body and deliver it to body cells. Humans also have developed social rituals and complex systems of communication, including language. Human language, which allows you to take this Biology course, is likely the most complex communication system in the animal kingdom. Turn to pages 144-145 of your reference book to learn about some of the life history characteristics of humans and other primates. Missing Metadata Humans have developed complex language and communication.

Humans obtain oxygen through the respiratory system.

Lined up perfectly, bare feet angled on a firm mat, karate students practice sidekicks in unison. They chant, counting in Japanese as their sensei, or teacher, walks, hands behind his back, checking everyone's posture. As the students exercise, they increase the demand on their muscles and their need for oxygen. The sensei teaches the students when to inhale and when to exhale, coordinating their body movements with the most efficient time to breathe. As oxygen in the form of the oxygen molecule (O2) enters their noses and mouths, where does it go from there? If oxygen is used in cellular respiration in all of the trillions of body cells, how does it get to them? In the following screens, follow the path of an oxygen molecule to its destination-the mitochondria located in a body cell. Missing Metadata Oxygen is moved thorough the respiratory system and circulatory system in the human body.

urine

Liquid waste that the kidneys have filtered. After leaving the kidneys, urine moves to the bladder.

All living things require a consistent source of energy to survive.

Living things need some form of energy to function. Plants get energy from sunlight. Most other organisms get energy from eating other organisms. Regardless of the source of energy, the body eventually uses the various foods for life processes. Cells transfer the energy in glucose molecules to the energy in ATP molecules, which cells then use to drive various life-sustaining mechanisms.

Flatworms also obtain oxygen by diffusion.

Looking at a flatworm, with its eyespots, head, and tail, you might think it has a mouth, through which it eats and breathes. Well, it does have a mouth, but it's located in the center of its body at the end of a long, protractile pharynx. As strange as it seems, flatworms, and many other similar organisms, do not take oxygen in through their mouths. Like bacteria, flatworms take in oxygen by diffusion. Oxygen gas (O2) that is dissolved in water—not the oxygen in H2O—enters through cell membranes of the surface cells and diffuses through the rest of the body. That oxygen is used up in cellular respiration to produce ATP. Check out page 156 of your reference book to learn more about this process.

Many protists play important roles in ecosystems.

Many members of Kingdom Protista are microscopic organisms, too small to see with the naked eye. Yet they play central roles in many ecosystems. The oceans, for example, are home to countless types of photosynthetic protists. They make their own food through the process of photosynthesis. These organisms produce much of the oxygen that's in the atmosphere, and also form an important food source for other organisms in the ocean. Some of the more common photosynthetic protists in the oceans are diatoms and dinoflagellates, as well as several types of protists informally known as algae. Algae are autotrophs Opens in modal popup window , but some other protists in the ocean are heterotrophs Opens in modal popup window , or organisms that must consume other organisms. Together, these types of protists form the base of the marine ecosystem, and support organisms as small as snails and as big as whales.

Many other animals inhale oxygen through internal lungs. Breathing Changes Amphibians can often absorb oxygen through their skin if necessary. In the early stages of life, young amphibians such as tadpoles have gills that are later replaced by lungs.

Many more complex organisms, including all amphibians, reptiles, birds, and mammals, have evolved an internal system for obtaining oxygen through an internal organ called the lung. This spongy structure is involved in the delivery of oxygen to cells. Think about the following questions: Why do more complex organisms need an entire organ system to obtain oxygen? Why do they need more oxygen overall? Why wouldn't diffusion be an effective form of obtaining oxygen for humans and other large animals? If lungs are located in the chest, how does oxygen reach body parts located farther away, such as toes and tails? Complex organisms, including all amphibians, reptiles, birds, and mammals, have evolved lungs to help absorb oxygen.

3.05 Protists and fungi are two diverse groups of eukaryotes.

Many parts of the world around you—from the air you breathe, to the trees in your neighborhood, to the bread you use to make a sandwich—depend entirely on eukaryotic organisms, some of which you might have never noticed before. A group of eukaryotes called protists both fills the world's oceans and is found on land; some protists generate oxygen through photosynthesis. Another group of eukaryotes called fungi helps plants absorb nutrients from the soil and causes bread to rise.

Many organisms produce solid and liquid waste.

Most complex organisms generate solid and liquid waste. Solid waste, called feces, comes from indigestible foods, dead cells, and other larger physical matter. In organisms with a complete digestive tract, feces Opens in modal popup window are expelled through an anus. Liquid waste, called urine, is produced when blood is filtered, removing products from protein production and other metabolic processes. Among other things, urine Opens in modal popup window in fish and mammals contains urea, a nitrogenous compound produced during protein metabolism. It is a liquid. In insects, reptiles, and birds, urine converts nitrogenous compounds into an insoluble compound called uric acid. Therefore, even though it starts out as liquid, the end waste is actually a solid. Missing Metadata Humans generate so much bodily waste (feces and urine) that municipalities need to create huge facilities to treat and detoxify the sewage.

The great variety of plants on earth is the result of millions of years of evolution.

Much of the story of plants is about how plants became less and less dependent on water with the evolution of structures such as vascular tissues, seeds, and pollen. The diversity of plants on earth today is reflected in the wide range of plants found in environments ranging from arctic tundra to tropical forests.

Humans need oxygen for the same reason other living things do: to make ATP in cellular respiration.

Once the oxygen has diffused across the capillary membrane into the body cells, where will it be used? Remember the small organelle in cells that is the powerhouse for the cell, the mitochondrion? Within cells, oxygen winds up in the mitochondria as critical participants in cellular respiration. ATP and the usable energy it carries supply each cell with life-sustaining fuel needed to carry out all of the cell's functions. The karate student's leg muscles could not kick without ATP energy, and your cells cannot create ATP energy efficiently without the oxygen provided by your respiratory and circulatory systems.

Some organisms depend on other organisms to help digest their food.

Picture horses munching on hay, cows chewing mouthfuls of grass, or sheep and goats nibbling on weeds. What's unusual about those animals? Despite the fact that plants are the exclusive diet of the animals, the digestive system of a cow, horse, sheep, and goat cannot break down cellulose, a major component of plant matter. In fact, no herbivore on earth carries enzymes capable of digesting cellulose—not even termites, which eat decaying wood. Instead, the digestive systems of plant-eating animals are filled with millions of bacteria that break down cellulose. The bacteria digest the cellulose, and in return they get a nice, safe place to live. Missing Metadata Plant-eating animals rely on bacteria in their digestive system to break down the cellulose in the plants they eat.

Human digestion breaks down food physically and chemically in a multistep process.

So you've stuffed a big piece of pizza into your mouth and begun to chew. What happens next? The first step of digestion begins when enzymes in your saliva start breaking down the carbohydrates in the food. As food moves through the organs of your digestive system, several other enzymes play a role in breaking down the various components. Explore the online digestive system to find out what happens to your food at each stage of digestion. Pay particular attention to page 151, which is a chart of the enzymes in your digestive system. Also turn to pages 149-151 of your reference book and keep your book open to this page throughout the lesson, and study the name and function of each enzyme.

Most plants and animals respire aerobically.

The energy required by all animals and plants to live and grow is provided by the chemical process called aerobic respiration. Most plants and animals breathe oxygen, which is then combined with glucose to form carbon dioxide and water and release energy. Now go on to watch a video to see how the energy required by all animals and plants to live and grow is provided by the chemical process called aerobic respiration. Transcript (Video) Screen 1: 00:00:00.00 Narrator: All animals and plants need energy to live and grow. They get this energy through a process known as respiration, a chemical reaction which releases energy from food. 00:00:20.00 Narrator: All living things respire, all the time, even when they're asleep. Most plants and animals respire aerobically, which means they use oxygen. This combines with glucose to form carbon dioxide and water. 00:00:40.00 Narrator: But, at the same time, energy is released. It's this energy which allows plants and animals to move and grow. Transcript (Video with Audio Description) Screen 1: 00:00:00.00 Description: A series of images: A herd of zebras, a lion, cheetah, a fruit tree, a human baby, people walking in a city, athletes racing on a track, goats eating shrubs, and pigs sleeping. 00:00:19.00 Narrator: All animals and plants need energy to live and grow. They get this energy through a process known as respiration, a chemical reaction which releases energy from food. 00:00:34.00 Description: A series of images: A pink flower, woods with a large patch of blue flowers, sunlight through the leaves of a tree. 00:00:43.00 Narrator: All living things respire, all the time, even when they're asleep. Most plants and animals respire aerobically, which means they use oxygen. This combines with glucose to form carbon dioxide and water. 00:01:03.00 Description: The chemical formula is, glucose, which is, C, subscript 6, baseline, H, subscript 12, baseline, O, subscript 6, baseline, plus oxygen, which is, 6 O, subscript 2, baseline, arrow, carbon dioxide, which is 6 CO, subscript 2, baseline, plus water, which is 6 H, subscript, 2, baseline O. 00:01:37.00 Narrator: But, at the same time, energy is released. It's this energy which allows plants and animals to move and grow. 00:01:45.00 Description: An arrow coming down from the equation points to 2880 kJ. Ending Time: 00:01:53.00

In humans, digestion begins in the mouth.

The first step of the physical breakdown of that piece of pizza begins when you take that first bite. Your teeth have a more important function than just giving you a beautiful smile. You probably use your canine and front teeth to tear a bite off that slice of pizza, and then you use your molars to chew it until it is small enough to swallow. Recall that humans are omnivores, so their variously shaped teeth can break apart many different kinds of food. Missing Metadata Omnivores, including humans, have variously shaped teeth that process different kinds of food.

Bacterial waste plays a major role in human existence, naturally and commercially. Single-cell organisms excrete wastes via exocytosis. Wastes are enclosed in a vesicle. The vesicle attaches to the cell membrane. The cell membrane opens.

The simplest form of waste disposal occurs in the simplest life-forms-single-cell organisms. Because their entire body is one cell, they simply dump out waste through the cell membrane in waste-carrying vesicles Opens in modal popup window . Remember, this process is exocytosis Opens in modal popup window . The enormous numbers of bacteria on earth produce immense amounts of waste. The surprising truth is nearly all this waste is beneficial, and is even harnessed by humans for commercial and industrial purposes. Each bacterial waste product has a distinct odor, or flavor, depending on the species and the food source. For example, the smells under your arm, on your feet, or from your mouth are all odors of bacterial waste. Bacterial waste is used in the production of many foods, such as cheese, yogurt, vinegar, soy sauce, and pickles. Startling discoveries revealed the power of certain bacteria to degrade toxic materials, and have been used to clean up oil spills, garbage dumps, chemical contamination, and even radioactive waste. It seems that for almost any material, natural or man-made, there is a bacterium that can break it down.

Gymnosperms are plants whose seeds do not form inside an additional structure. Gymnosperm Medicine Scientists at medical centers across the United States are studying whether extracts from the bark of pine trees and their relatives can help treat conditions such as cancer and high blood pressure. In fact, the drug Taxol, which comes from a the Pacific yew, is used to treat breast cancer.

The term gymnosperm means naked seed, and is a reference to the way in which gymnosperms produce seeds. Their seeds are usually held inside reproductive structures called cones, which release them directly to the environment when conditions are right. Pines, yews, and several other types of trees are classified as gymnosperms Opens in modal popup window : vascular plants that produce seeds. Gymnosperms include the oldest trees on earth-as you can see on page 137 of your reference book, bristlecone pines are more than 5,000 years old. Another gymnosperm, the giant sequoia, is the largest tree on earth. In the cones of this ponderosa pine, the paper-thin seeds are located between the thick scales of the cone.

A phylogenetic tree shows how groups of organisms are related through common ancestry.

The whole reason why scientists develop classification schemes is to help better understand the phylogentic relationships among the organisms on earth. Memorizing names is not what's important: Standard systems of naming ensure that everyone is talking about the same organisms. The evolutionary history, or phylogeny, of any group of organisms can be displayed in a diagram called a phylogenetic tree, like the one on pages 130-131 of your reference book. Each point of divergence on a phylogenetic tree shows an event in which two evolutionarily related groups split from a common ancestor.

Today, scientists classify life on earth into a ranking of groups. Each group is more inclusive than the one that precedes it.

Think about how you've organized all the things in your bedroom. What are some of the broadest, most inclusive categories? Perhaps those categories include books, music, and clothes. What are some of the categories that fall under the larger category of clothes? Clothes categories might include shirts, sweaters, pants, and socks. And within each of those categories are still smaller categories. You might have wool socks and cotton socks in your sock category. Your shirts category might include button-down shirts, long-sleeved shirts, and short-sleeved shirts. In the same way that you might organize the things in your bedroom, scientists organize life into ranked categories. You learned that chestnut-sided and yellow warblers are different species, but they belong to the same genus. They have many characteristics in common; therefore, they are placed in many of the same taxonomic categories. They differ at the species level, but they are grouped together at the genus level.

3.14 Waste Removal Waste excretion in living things helps maintain homeostasis throughout the entire body. waste removal is important for homeostasis by ridding organisms of unneeded materials and toxic materials

What do a leaf, underarm odor, a flatworm's mouth, and vinegar all have in common? In some way, they are all related to this lesson on waste. Every organism must rid itself of unneeded materials, its waste products. Each major group of living things tends to excrete waste in a similar manner.

Fungi share several unique features that unite them as a kingdom.

What does the antibiotic penicillin have in common with athlete's foot? They're both produced by various species of fungi Opens in modal popup window -the next kingdom of eukaryotes you'll learn about. Explore the phylogenetic tree on page 131 of your reference book, and you'll find that fungi have a common evolutionary history. The tree on page 134 shows that fungi are divided into five categories that all share a common ancestor. Page 135 shows a few representative fungi. They look very different from one another, but they do share several basic characteristics: Fungi are heterotrophs. They do not perform photosynthesis Fungal cells are surrounded by cell walls that are made of chitin. Chitin sets fungi apart from plants, whose cell walls are made of cellulose. Fungi are made up of cells arranged in filaments.

Living things depend on a consistent source of oxygen for cellular respiration. Their survival depends on it. Single-cell organisms, such as this Euglena, absorb oxygen through diffusion. Plants, such as this oak tree, obtain oxygen through pores called stomata in their leaves. Flies and other insects acquire oxygen through small holes called spiracles in their sides. In fish, water flows over organs called gills where oxygen is absorbed. More complex animals, such as this snowshoe hare, acquire oxygen through their lungs.

What's the big deal about oxygen anyway? The more energy, the more an organism can do. Oxygen, along with glucose, is an important part of producing energy. Just as a great job or a winning stock makes money, oxygen is one component necessary to make energy. Usable energy, stored in ATP, must be generated constantly by each and every cell. ATP fuels all cellular functions, and without it a cell dies. The manner in which living things obtain oxygen varies quite a bit.

Digestion involves taking in food, digesting it, and distributing the end product to cells for energy and other needs.

Whether it is a snake, a human, a clutch of flesh-eating larvae, a grazing cow, or a brightly colored butterfly, the digestive purpose and pathway are important for processing energy and nutrients. The basic concept of digestion is the same in all animals: Find food. Break it down. Break it into nutrients and chemical components. Absorb the components into the body. Move glucose into cells so cellular respiration can generate usable energy.

Domains Archaea and Bacteria both include single-cell prokaryotes. Archaeans can live in extreme environments such as near thermal vents at the bottom of the ocean.

Why did Woese suggest that single-cell prokaryotes be grouped into two very different categories, archaeans and bacteria? After all, they're both single-cell organisms that lack a nucleus. He discovered differences telling that they diverged from each other very early in each group's evolutionary history. Archaeans have unique RNA sequences and unique membrane structures that allow many of them to live in extreme habitats-thermal hot springs, volcanic vents, acidic pools, and extremely salty water-where nobody would expect to find living organisms. The archaean methanogen lives in the digestive tracts of cows. It produces the greenhouse gas methane inside cows' bodies, which cows occasionally release by belching. Bacteria include many organisms that cause disease, such as certain strains of E. coli, which sickens approximately 73,000 people each year. Bacteria aren't all harmful, though. They also play important roles as decomposers in ecosystems, and bacteria living in your body help break down some food. Turn to pages 132-133 of your reference book to read more about archaeans and bacteria.

Maintaining homeostasis includes the removal of waste products.

Why do living things need to get rid of waste? Homeostasis. Keeping a balance is critical to the health of a living thing, which includes not allowing waste materials to build up, take up space, and reach toxic levels. Even gaseous waste can be poisonous in high levels. As cells work to produce proteins and carry out all functions, waste materials are inevitably generated. Excretion of waste takes many forms, but each group of organisms generally has the same manner of waste removal.

Sponges were some of the first animals to evolve on earth.

You might not guess that a sponge is an animal, but in fact, a sponge is just as much of an animal as you, a butterfly, or a tiger. But what makes a sponge an animal? Like all animals, sponges are multicellular and heterotrophic. Sponges belong to phylum Porifera, a word derived from the Latin word for pore. It's a reference to the structure of a sponge's body, which allows the passage of water into and out of the body. Sponges use their pores to feed and reproduce. Most sponges live in the ocean, though many species live in freshwater. Sponges feed by filtering microscopic organisms from the water. Explore the process by which a sponge feeds. Filter Feeding in Sponges Opens in modal popup window .

feces

solid waste that leaves the body

exocytosis

the movement of materials out of a cell by use of a vesicle

Many mammals use urine to mark their territory.

A cheetah turns away after picking up the urine scent of another. The massive cat knows this land is claimed, and rather than risking injury or even death fighting for the space, it moves on. Someday soon, the cat may have no other choice than to fight as human encroachment continues to shrink its habitat each year. Within the urine of mammals is a distinct scent so specific that each individual has its own urine-smell fragrance. Many animals, such as cats and dogs (including wolves), mark their territory with urine. By staking an area as their own, these animals lay down boundaries in which to hunt and mate, which is often necessary because large predators need a lot of space to hunt and consistently find prey. Too many top-of-the-food-chain predators in one area means intense competition for food. In addition to removing waste, some animals use urine to mark their feeding and breeding territories.

Many birds remove their waste in such a way as to prevent bacterial growth and disease. Seed Transportation Birds and other animals often eat seeds that are excreted whole. By first transporting the seeds to a new place and releasing them in a pile of nutritious waste, the seeds have an advantageous beginning in new surroundings far from the parent plant.

A mother robin arrives at the edge of the nest, looking down on three competing, wide-opened mouths that are waiting to be stuffed with juicy earthworms or crunchy beetles. Yet, its many jobs include more than feeding its ravenous young. After all that insect stuffing, lots of waste comes out of each baby. Many birds keep their nests clean and tidy by removing the waste, often right out of the cloaca of the young—before it even has a chance to drop into the nest material. Otherwise, bacteria and other microorganisms can grow and cause disease to the mother bird and its offspring. Missing Metadata The young of some bird species excrete waste in fecal sacs that make it easier for a parent bird to remove the waste from the nest.

Organisms must break down the food they eat into various substances and compounds before it can move into body cells. Flies and Food... The next time a fly lands on your picnic table, remember that flies, like spiders and many other animals, begin digestion externally by regurgitating digestive juices onto food they are about to eat.

A spider vomits digestive fluids onto its insect prey to soften the exoskeleton and body parts. But when the spider eats, its body must break down the insect into nutrients and other usable compounds. The breaking down of food into chemical components is called digestion. The ultimate goal of digestion Opens in modal popup window is the production of molecules that the body can absorb. Some of those molecules will be used to build fats, proteins, and carbohydrates. Others will be sent to cells as glucose for the production of ATP—the energy that organisms need to perform all life functions.

Today, taxonomists use DNA evidence to help classify organisms. Recent DNA studies suggest that the New World turkey vulture (left) is more closely related to the wood stork (center) than it is to the Old World griffin vulture (right).

A vulture and a stork don't look very similar, but recent DNA studies suggest they're more closely related than you might suspect. In fact, DNA evidence has uncovered many new patterns. Scientists comparing DNA sequences among birds have found that despite differences in physical appearances, many birds are more closely related to one another than they realized. Given new DNA evidence, bird taxonomists have proposed new classifications that would change some of the historical systems that have been around for hundreds of years.

Adenosine triphosphate Cellular Respiration glucose---glycolysis-krebs cycle-electron transport chain-atp

ATP; the molecule that delivers usable chemical energy for almost all processes and reactions that a cell must undergo to survive

Ferns live in many locations around the world.

About 12,000 species of ferns live on earth today, and range from the tiny Azolla to the tree ferns of Australia, Malaysia, and New Zealand. You can see some ferns on pages 142-143 of your reference book. Tropical and temperate rain forests, such as the rain forests of Washington's Olympic National Park, are home to many species of ferns. The bracken fern, which you just read about, is an important food source for animals such as deer and rabbits, and it also provides habitat for many small forest animals. Missing Metadata Tree ferns in the New Zealand countryside

A highly branched digestive cavity allows the flatworm's body cells to absorb nutrients. The flatworm's gastrovascular cavity branches throughout the body. Enzymes in the cavity break down food into molecules that the tissues can absorb. The gastrovascular cavity also stores waste products until they can be expelled back through the mouth. A Flatworm Parasite: One kind of flatworm, Clonorchis sinensis, is a parasite that lives in the bile ducts of the human liver. At a certain stage in its life cycle, the organism may exist as a cyst in the muscle tissue of a freshwater fish. If the fish is not cooked thoroughly and a human eats the fish, the cyst can migrate from the human's small intestine into the liver, where it matures and then lays eggs to produce more worms. The common name for C. sinensis is the human liver fluke.

After a flatworm dissolves its food, it sucks the liquefied food into its gastrovascular cavity. There, more enzymes break the food down even further. A flatworm's gastrovascular cavity has many branches that reach all areas of the body. The branches carry nutrients to all body cells, where they are absorbed directly into the cells. Thus, the flatworm differs from organisms that have a circulatory system to transport nutrients through the blood. The large surface area of the branches ensures that all of the flatworm's body tissues receive nutrients, and that the cells receive the glucose needed to produce ATP and the amino acids needed to build proteins. Turn to page 148 of your reference book to learn more about the flatworm's digestive system.

Alveoli have a large surface area.

After traveling through the air passageways of the respiratory system, the air you breathe in winds up in an alveoli sac—a small, bubble-like structure filled with other oxygen and carbon dioxide molecules. These alveoli are where oxygen and carbon dioxide move into and out of the bloodstream through very small blood vessels called capillaries. In the illustration of human lungs at right, zoom in to examine the relationship between alveoli and capillaries Opens in modal popup window . Because each alveolus is like a sac,it has a large surface area. The large surface area allows for more gas exchange. Combined, the surface area of the alveoli in your lungs is enough to cover a tennis court.This amazing design is important because your body cells require a constant exchange of oxygen and carbon dioxide.

Humans produce three main types of waste: carbon dioxide, urine, and feces. Respiratory System- nasal passages, mouth, trachea, and lungs- gaseous waste is expelled through the respiratory system. Digestive System- liver, stomach, large intestine, small intestine, colon, rectum, and anus- Solid wastes, or feces, are expelled through the digestive system. Excretory System-kidneys, ureter, urinary, bladder, and urethra- liquid waste, or urine, is expelled through the excretory system.

Although this lesson uses the human body as an example, keep in mind that all mammals share similar waste removal systems. Other animals, too, have many of the same organs and mechanisms for removing waste. Wastes produced by humans are of three basic types: gaseous waste: carbon dioxide from cellular respiration liquid waste: urine, produced by the kidneys and containing nitrogenous materials solid waste: feces, compacted in the rectum as a result of food digestion Each form of waste is produced by a separate organ system, and removed from the body in different locations related to that system. Waste removal is critical in maintaining homeostasis in the body.

Some organisms are adapted to digest different foods at different stages of life.

As the spring sun warms the African savanna, a female zebra gives birth to a single foal. The newborn zebra craves only its mother's rich milk. Like all other mammals, zebras evolved to begin life needing only one type of food-milk. Rich in fat and nutrients, milk is the only food that young mammals can digest. The digestive systems of mammals change as the young develop, however, and eventually the growing animals can handle different foods. The same is true of many organisms. Caterpillars, for example, gorge on leaves. But when they metamorphose into butterflies or moths, they feed on sugary flower nectar. Whatever the food source—milk, leaves, or nectar—the basic pathway of digestion is the same. The digestive system breaks down food and the body takes in nutrients that move into body cells.

Humans seek out and consume many types of foods. Edible Insects: Though you might not care to eat an insect yourself, insects are actually a good source of protein and other nutrients. In Africa and many countries, including Japan, New Guinea, India, and Australia, insects are part of the diet of many native peoples. If you'd like to learn more about insects as food, visit the Activity Resources in this lesson and read the article "Edible Insects."

As you wander through an African village, you come upon a vendor frying food in an open-air market. The tempting fragrance makes your mouth water, so you buy a small packet of the golden-brown treats. As you bite down into a delicious-looking morsel, the vendor shows you the source of his popular local delicacies—a bucket of plump, squirming caterpillars. Humans and many other animals survive by eating an enormous variety of both plants and animals—including insects. Such an animal is known as an omnivore Opens in modal popup window . An animal that eats only other animals is a carnivore Opens in modal popup window . One that eats only plants is an herbivore Opens in modal popup window . Missing Metadata In many cultures, insects are a common food.

Every species on earth has a unique taxonomy. Phoeniconaias minor Domain Eukarya Kingdom Animalia Phylum Chordata Subphylum Vertebrata Class Aves Order Ciconiiformes Family Phoenicopteridae Genus Phoeniconaias Specific epithet minor

Birds are eukaryotes, so at the broadest level of classification, they are included in Domain Eukarya, which includes animals, plants, fungi, and protists. At some point in the distant past, animals, plants, fungi, and protists shared a common ancestor. Birds are animals, placing them in Kingdom Animalia, along with organisms like honeybees, bears, and jellyfish. Since they belong to this kingdom, birds are more closely related to jellyfish than they are to plants. Unlike jellyfish, though, birds have a backbone, which places them in both phylum Chordata and subphylum Vertebrata. Since birds have feathers and hollow bones, scientists place them in class Aves. Reptiles do not have feathers; therefore, they are not in Aves. This flamingo has long legs and a long beak and is standing in the water. These clues help us know that it is in the order Ciconiformes. The family name Phoenicopteridae includes all flamingoes, and the genus name and specific epithet, Phoeniconaias minor, indicates the bird is the lesser flamingo.

Some species of prokaryotes are anaerobic, or capable of living without oxygen.

Botulism is a serious pathogenic disease that leads to paralysis of the muscles. Clostridium botulinum, the bacterium responsible for botulism, is a kind of prokaryote that can live without oxygen. Anaerobic bacteria are adapted to live in places where oxygen is not available. To some anaerobes, oxygen is poisonous and can kill them. To others, such as this species, oxygen is benign. A few bacteria, such as the one that causes botulism, are among the only organisms on earth that can live without oxygen.

Scientists organize all life on earth into groups based on shared traits.

By using both physical and molecular evidence, scientists organize all life on earth into categories that reflect evolutionary relationships. The domain is the broadest category into which life is organized, and scientists today divide life on earth into one of three domains. Within each domain, organisms are further subdivided into smaller and smaller groups.

Scientists use a unique, two-part name to refer to every species on earth. Pictures Chestnut-sided warbler Dendroica pensylvanica Yellow warbler Dendroica petechia Blackburnian warbler Dendroica fusca Black-throated blue warbler Dendroica caerulenscens Format Matters Even the format of a scientific name matters. Scientists always write the scientific name in italics. The genus name starts with an uppercase letter, while the specific epithet is in all lowercase letters. You'll see a few more examples throughout this lesson.

Carolus Linnaeus developed a two-part naming system to refer to all living organisms. The two-part name identifies a species and consists of a genus name and specific epithet. The specific epithet also is called the descriptor; in the past, it was also called the species name. Scientists prefer to use the term specific epithet to distinguish one species from another species in the same genus. Wood warblers are among some the most colorful, active, and intriguing birds in the Western Hemisphere. Based on similarities in physical characteristics such as size and shape, number and structure of feathers, and certain shared behaviors, scientists have identified several different genera. Within the genus Dendroica, scientists have identified about 20 different species based on differences in plumage color, song, and mating preferences. The species or scientific name for each warbler consists of the genus name Dendroica, which implies shared characteristics, and a specific epithet, which implies differences. Explore some of these related, yet very distinct, species of warbler.

Humans excrete three basic types of waste: carbon dioxide, urine, and feces. Separate organ systems produce and excrete each type.

Cellular respiration produces carbon dioxide, the gaseous waste that humans excrete through the mouth and nose. Protein digestion, with the help of the liver, results in urine, which is liquid waste produced by the kidneys. Urine is excreted from the urinary bladder out of the urethra. Feces build up in the rectum, until enough pressure encourages excretion out of the anus. Waste excretion is a critical component of homeostasis in humans and all living things. As substances are taken in and used, waste must continually be removed to make way for the supply of energy-packed food and important gases necessary for survival. Without functioning excretory systems, humans and all other organisms could not maintain health and homeostasis.

Although Domain Bacteria is very diverse, bacteria share some basic characteristics.

Despite their differences, bacteria Opens in modal popup window share some basic traits that set them apart from either eukaryotes or archaeans. Bacteria are prokaryotes. They are all single-cell organisms lacking a nucleus. Their DNA is one single, circular chromosome. Bacteria are surrounded by a strong cell wall made of a molecule called peptidoglycan. Bacteria have distinct amino acids in some of the proteins they produce. Many bacteria reproduce using a process called binary fission. In binary fission, the bacterial chromosome replicates, and the bacterium pinches into two separate cells. Each new bacterium receives a copy of the single chromosome. Review the structure of a typical bacterium

Inhalation and exhalation provide oxygen and remove carbon dioxide.

Doesn't it seem like you breathe out the same air that you breathe in? You don't feel the gas exchange that is occurring—but it is, of course. Breathing in, or inhalation, brings in air that is a mixture of many things, and your lungs take out the oxygen. Breathing out, or exhalation, rids the alveoli of carbon dioxide, along with the other gases not needed by the body. Taking a breath may seem simple, but the entire process of moving oxygen in and carbon dioxide out involves the respiratory system, circulatory system, and diffusion. Missing Metadata Aerobic exercise conditions your heart and lungs to more efficiently move oxygen into your cells and carbon dioxide out of your body.

The respiratory system excretes carbon dioxide.

Dripping with sweat and muscles aching, with mouth open to gulp down oxygen, the newest member of the girl's track club finds strength for a last sprint to upset the expected winner. With a stunning victory, she crosses the finish line, panting as the crowd cheers. With each massive exhalation, the new champion can't help but to expel waste over her adoring fans, but not in the form that you normally associate with the term. Start with the least obvious type of waste—carbon dioxide. During cellular respiration, glucose and oxygen produce ATP, and carbon dioxide is a waste product of this process. Because cells constantly need ATP, carbon dioxide is constantly being produced. Removed from the blood and sent to the lungs, carbon dioxide is expelled the same way that oxygen came in. In the lungs, excess carbon dioxide is removed from blood and expelled through the trachea, nose, and mouth.

3.01 Classification and Taxonomy

Every year, scientists exploring different habitats on earth discover species that have never been documented. Recently, scientists exploring the ocean floor found a strange Christmas tree-shaped creature that was like nothing they had seen before. Scientists turned to taxonomy—the science of classifying organisms based on shared characteristics—to identify the spiraled creature as a fantastic worm. Scientists look to the similarities and differences among organisms to help them develop a broad picture of all life on earth.

Domain Archaea includes another broad group of prokaryotes.

Explore the phylogenetic tree on page 133 of your reference book. Domains Archaea and Bacteria split apart from each other all the way at the base of the tree. This split shows that scientists believe the two groups, or lineages, split apart from each other very early in the evolution of life. While both domains are made of prokaryotic cells, the two groups differ in several fundamental ways. Archaean cells are protected by unique cell walls made up of lipids unlike those found in either bacteria or eukaryotes. Unlike bacteria, archaean cell walls do not contain peptidoglycan. Archaeans and eukaryotes also have similar proteins in their ribosomes. These proteins are different from those found in bacterial ribosomes. Based on these characteristics, as well as DNA and other molecular evidence, scientists have determined that archaeans Opens in modal popup window are more closely related to eukaryotes than they are to bacteria. Now, explore the phylogenetic tree.

Ferns are seedless vascular plants. Mosses are nonvascular seedless plants. They grow very close to the ground, and require water for reproduction. Mosses do not have true roots, stems, or leaves. Ferns do have vascular tissue to transport materials. They do have roots, stems, and leaves. Like mosses, ferns do not produce seeds for reproduction.

Ferns have existed on earth for more than 390 million years, since the Age of Dinosaurs. Their bodies are more complex than the bodies of mosses: Ferns have vascular tissues Opens in modal popup window , specialized tissues that carry water and nutrients throughout the plant. Scientists call these tissues xylem and phloem. They form a network throughout the plant, carrying water and nutrients to all its parts. Water pulled up from the soil travels through xylem, while the sugars produced through photosynthesis travel in the phloem. Vascular tissues allow ferns to grow much larger than mosses, because ferns do not need to rely on simple diffusion to move materials in and out of their bodies. In some parts of the world, ferns even grow to the size of trees. Club mosses and horsetails are two other types of seedless vascular plants you may see in forests or marshy habitats. Unlike nonvascular plants, vascular plants have stems, roots, and leaves. Similar to nonvascular plants, vascular plants do not produce seeds.

The flatworm excretes solid and liquid waste. Flatworms ingest nutrients and expel waste through the same opening-the mouth, which is at the end of the pharynx. Solid wastes are collected and condensed in a flatworm's gastrovascular cavity and then expelled through the pharynx. Liquid waste is gathered in a system of tubules in a flatworm's body. Urine is released through the tubules to the outside of the body. Proteins as Waste Recall that the metabolic system produces many proteins that have functions for an organism. Those protein structures eventually need to be replaced, and the old ones become waste.

Flatworms bring food into the mouth, absorb the necessary nutrients, and then expel their waste out of the same hole—the mouth. Each cell releases its solid waste products that are collected into the gastrovascular cavity. From here, they are condensed and released. Other organisms expel waste in the same manner as the flatworm, such as the sea star, hydra, and jellyfish. For liquid waste, the flatworm has an extensive, branched system. Turn to page 153 of your reference book to review the fluid excretory system of the flatworm. After taking in fluids from the environment, wastes from the worm's metabolic system are collected into this system, along with excess water. The flatworm's excretory tubules expel liquid waste directly out of pores in its outer layer.

Some flatworms live freely, while others are parasites that live inside the bodies of other animals.

Flatworms can be parasitic or free-living. They are divided into three main groups, as summarized on pages 140-141 of your reference book. Nearly 20,000 species of flatworms live on earth today in freshwater rivers and lakes, in the oceans, and inside the bodies of other animals. While free-living flatworms hunt and feed on other organisms, flatworms such as tapeworms have a parasitic life history. They live inside the bodies of other organisms and consume their tissues or consume the same food the host organism eats. Scientists estimate that 200 million people around the world are infected with tapeworms. These different types of flatworms provide examples of the variety of life histories seen in this group of animals. Missing Metadata These parasitic tapeworms live inside other organisms.

3.02 Modern Classification Scientists organize all life on earth into groups based on shared traits. Life on earth is divided into 3 domains: archaea, bacteria, and eukarya which are divided into smaller groups.

For years, scientists have been sounding alarms about increasing levels of greenhouse gases in the atmosphere. These gases trap heat in the atmosphere and reflect light back down to earth that would normally be reflected into space. Methane is one of those gases. Microbes living in cows' digestive tracts produce methane, which cows release by belching. Those microbes belong to a recently described taxonomic category that you'll learn about in this lesson.

The first plants evolved between 400 and 500 million years ago.

From the tallest sequoia in California to the mosses covering the forest floor in Olympic National Park in Washington State, all plants on earth descended from a common ancestor. Most scientists agree that the ancestor of today's plants was a photosynthetic alga, a protist that lived in aquatic habitats hundreds of millions of years ago. Since the first plants began to grow on land, they've come to dominate nearly every habitat on land. The transition to life on land became possible as plants acquired a few key adaptations, which you'll learn about in this lesson. Unlike their algal ancestors, plants needed to control water loss, find new ways to reproduce, and support themselves on land. The story of plants, as you'll see, is largely one about adaptation to life on land. Missing Metadata The Olympic National Park in Washington is a unique forest composed of plants adapted to life on land.

The names of organisms grew very complicated over time. Once called Apis pubescens, thorace subgriseo, abdomine fusco, pedibus posticis glabis, untrinque margine ciliatus, the European honeybee is now Apis mellifera. A Common Name The term common name means any given name to an organism that is not its scientific name. Common names are great for everyday use. Puma, mountain lion, Nittany lion, and cougar are all common names for the same thing. But, common names vary from place to place and, therefore, are rarely used by scientists. The scientific name Felis Concolor is the universal name that means the same animal to scientists worldwide.

From the time of Aristotle until the middle 1700s, scientists gave organisms descriptive names based on some of their characteristics. As you can imagine, this system became quite cumbersome, with some organisms being labeled with 10 or more different words. Adding to the confusion, there wasn't always agreement on what to call different organisms. Sometimes, two different scientists would use different names for the same organism. Others might shorten the longer name. This disagreement created new problems: How could two scientists know they were talking about the same organism?

Fungi play important roles in ecosystems as decomposers.

Fungi grow on trees by sending filaments deep into the tree. Many fungi feed on dead and decaying plant matter such as fallen trees or leaf litter. These and other fungi play a crucial role as decomposers in ecosystems. Not only do they break down dead plants and animals, but they also release nutrients back into the soil, where the nutrients become available for other species. Fungi are very successful at finding food. Leave a loaf of bread or an orange sitting out for too long, and it will grow a layer of fuzz. That fuzz, commonly called mold, is a type of fungus. Spores, which are the reproductive structures of fungi, are found in the air everywhere, and they frequently will colonize the foods in your kitchen if you leave them out for too long. In nature, as soon as an organism dies, fungal spores fall on it; when the conditions are right, they germinate and begin the process of decomposition. Explore fungi growing on a tree trunk.

Some fungi live in symbiosis with other organisms.

Fungi play another important ecological role. Some fungi live closely with plants, and both species benefit by swapping nutrients. This relationship is called a mycorrhiza, and it forms between the filaments of a fungal body and a plant's roots. Scientists suggest that a plant provides the fungus with carbohydrates produced during photosynthesis, and the fungus helps move soil minerals to the plant's roots. The relationship is especially important to many trees. Another type of fungal partnership you may have heard of is lichen Opens in modal popup window . Lichen is a fungus that grows in association with green algae or other photosynthetic organisms. Each partner in the relationship provides the other with important nutrients: The photosynthetic alga provides carbohydrates to the fungus, and the fungus provides minerals and protection to the alga.

Ferns and other plants provide their own oxygen from photosynthesis and take it in through stomata.

Generally, you probably think of plants as oxygen producers. You breathe oxygen in, and plants release it. Your release carbon dioxide, and plants take it in. The perfect cycle. But, that's not the whole story. Like all other cells, plant cells need ATP to function. So, to break down their self-made sugars, they need oxygen as all other organisms do. Plants obtain oxygen in two ways: They use the oxygen they produce during photosynthesis. They import oxygen from the atmosphere through stomata, small openings on the undersides of their leaves. Stomata Opens in modal popup window have cells around them called guard cells that have the ability to open and close. When open, gases enter and leave. Turn to page 157 of your reference book for more information about plants and oxygen.

Insects, reptiles, and birds excrete solid waste. Uric Acid The familiar white substance in bird droppings is uric acid.

Glittering with conspicuous whiteness in the morning sun, the cliff homes of thousands of breeding seabirds in Iceland look like snow. Yet, in reality it is waste excretions built up into almost artistic formations. The nitrogenous waste product of insects, reptiles, and birds is solid, and their excretions are often combined together with fecal waste—that is why bird and reptile droppings are often a swirl of white and brown or black. The hole where waste comes out in reptiles, birds, and fish is called the cloaca. Insects living on land also have solid urea waste, but do not always excrete it. While insect fecal waste is always removed, the urea is sometimes stored. As with all organisms, waste removal in these groups is essential for maintaining homeostasis. Constantly produced waste cannot be allowed to build up within an organism's body for long. Missing Metadata The white, lacy designs carpeting these rocks are made of feces excreted by birds over long periods of time.

3.18 Oxygen and the Human Body In humans, oxygen travels from the lungs to the blood, which delivers it to all cells. Oxygen gas then diffuses into each cell. Human respiratory system consists of air passage ways to lungs which provide oxygen and remove carbon dioxide to and from body cells.

Have you ever had to pass out materials such as handouts in class or food at a party? Maybe you've had a newspaper route and delivered 200 papers per morning. Imagine having to deliver oxygen to trillions of cells every second of every day, 24 hours a day without stopping—that is the job your lungs and circulatory system undertake to keep oxygen available to each of your cells. Without it, your body cells could not survive.

People use fungi in many beneficial ways.

Have you ever noticed all the tiny holes in a piece of bread? Those holes are produced by tiny gas bubbles created by yeast, a microscopic type of fungus, during the process of breadmaking. Biologists also use yeast in many research studies. Yeast cells are easy to cultivate in a lab, and are frequently used when scientists need to study eukaryotic cells. For example, scientists at the Fred Hutchinson Cancer Research Center in Seattle have studied how yeast cells divide. They can use this information to help develop tests for cancer treatments. As you read earlier, some important antibiotics come from fungi. Antibiotics are drugs that kill bacteria, and the list of antibiotics extracted from fungi continues to grow. Important antibiotics that have been found in fungi include penicillin and cephalosporins. Cephalosporins are used to treat athlete's foot.

In the 1400s and 1500s, herbalists developed a plant classification scheme based on how plants were used. Otto Brunfels was among the first to clearly classify plants as those that do, or do not, produce flowers.

Herbalists, or people who use plants for medicinal purposes, began to use a newer classification scheme during the Middle Ages. They grouped plants according to how people used them: Were the plants edible? Were they poisonous? Did they have medicinal properties? The groupings may have helped herbalists of the time organize plants according to their assumed functional properties, but the groupings did not, for the most part, inform them about how plants are related, nor did that classification provide much information about the history of plants. Although those groupings later fell out of favor, some early herbalists did contribute to later understanding of characteristics that help classify plants. For example, the sixteenth-century German botanist Otto Brunfels divided plants into those that produce flowers and those that do not. Many years later, scientists came to recognize that production of flowers is a characteristic of a major natural group of plants, and that this single characteristic tells those plants apart from many others.

Arthropods are the most abundant animals on earth.

If you could put all types of animals on earth into a huge bucket and take out a handful, three out of every four of those animals would belong to the phylum Arthropoda-a huge group that includes lobsters, bumblebees, barnacles, and tarantulas. Arthropods live in nearly every habitat on earth, and are important as plant pollinators, sources of food, and serious pests. What do they all have in common? Arthropods have a hard, jointed outer covering called an exoskeleton. An exoskeleton is made of a tough polysaccharide called chitin. Arthropods have a complete digestive system, complex organ systems, and sophisticated behaviors. Explore the basic anatomy of a grasshopper in the online activity. Grasshopper Anatomy Opens in modal popup window . To explore the social behaviors of leaf-cutter ants, click here.

Monocots and dicots are the two main groups of angiosperms.

If you look closely at the leaves of many angiosperms, you'll notice that the veins in the leaves either are parallel to each other or form a branching pattern. These characteristics help differentiate between two main groups of angiosperms, monocots and dicots. Monocots are plants that produce a seed containing one embryonic leaf. Dicots are plants that produce seeds containing two embryonic leaves. Many of the grains you eat, such as corn, wheat, and rice, are monocots. So are flowers such as lilies and tulips. Read more about these two groups of angiosperms on page 137 of your reference book. Missing Metadata In the dicot leaf, the vascular tissue forms branching veins. The monocot grass leaf shows parallel veins.

Plants are classified into groups based on their structures. A seed is a protective structure that contains a plant embryo. The presence or absence of seeds is used to classify plants. Vascular tissues are specialized for water and nutrient transport. The presence or absence of these tissues is used to classify plants.

If you looked at a moss and a rosebush, you'd probably guess that they are classified into different groups. Your conclusion would be correct: While mosses and rosebushes are both members of the plant kingdom, they belong to different taxonomic groups within Kingdom Plantae. Two characteristics of plants dominate their classification: the presence or absence of a seed the presence or absence of vascular tissues You'll learn more about these groups in the remainder of this lesson.

Ferns make their own food. Pteridium aquilinum (Bracken Fern) fronds spores Spores are reproductive structures that travel on wind or in the water, helping ferns. This further helps ferns carry out their life functions while rooted to the ground. A fern spore is about the size of a pollen grain. A single fern frond may release 750,000 to 750 million spores in a year. Considering that most ferns have 10 to 20 fronds per plant. The number of spores that one plant can produce is staggering. Most ferns do not have stems above ground. Generally only the frond is visible. A frond is a single large compound leaf. The tiny leaf like structures making up the branches of the frond are pinnules, or leaflets. Photosynthesis, which takes place inside the fronds, produce the sugars the plant breaks down as an energy source. ROOTS reach into the soil and absorb water and nutrients.

If you take a stroll in a shady North American woodland, you may see a bracken fern (Pteridium aquilinum). This common fern, like the one pictured at right, grows in thickets on forest floors across much of the temperate world. Like all plants, ferns are multicell eukaryotes. Like the cells of all plants, fern cells are surrounded by a rigid cell wall. Fern cells also house a structure called a chloroplast, which contains chlorophyll. Chlorophyll is the pigment that allows plants to capture the sun's energy and use it to convert water and carbon dioxide to into glucose. Taken together, the fronds and roots allow the fern to spend its life in one location and still obtain the energy and nutrients it needs to carry out all of its life functions. Study some fern structures in detail. Study some fern structures in detail.

On earth, there are vastly more prokaryotes than eukaryotes.

If you were asked to describe the diversity of life on earth, you'd probably think of all the eukaryotes you know: birds, fish, clams, trees, flowers, and insects. But, eukaryotes-organisms made of cells with a nucleus and other membrane-bound organelles-make up just a fraction of the species alive on earth today. The vast majority of life on earth is made up of prokaryotes Opens in modal popup window , the single-cell organisms that are too small to see without a microscope. Two of the three domains of life include only prokaryotic organisms. These domains-Bacteria and Archaea-are made up of organisms as different from each other as they are from you. You might not guess it on the surface, but a closer look at the molecular and genetic makeup of the organisms in these two domains shows just how unique each is. Review the relationship of the domains Bacteria, Archaea, and Eukarya.

Mollusks live in marine and terrestrial habitats.

If you've ever been to the seashore, you've probably seen evidence of at least one major animal phylum: Mollusca, the mollusks. Snails, clams, and mussels are mollusks, as are octopuses and squid. Most of these animals live in marine habitats, though some clams and snails live in freshwater. Some snails even live on land. All mollusks have a muscular foot, soft bodies, and gills that they use for breathing. They also have a rough feeding appendage called the radula, which they use to scrape algae off rocks. Most mollusks are covered with a hard shell, though in some species, such as squid, this shell is reduced to just a tiny structure inside the body. To view the general anatomy of a snail and a clam, Explore the general anatomy of a snail and a clam: Anatomy of Mollusks Opens in modal popup window . Now, review the four different mollusks on-screen.

Protists have beneficial uses.

If you've ever eaten ice cream or cottage cheese, you've eaten a material produced by protists. Next time you're in the kitchen, look on the labels of some of the processed foods in the pantry or refrigerator. Chances are you'll see an ingredient called carrageenan. Carrageenan is a material extracted from red algae, large protists that live in the Atlantic Ocean. It is used as a thickener or as a stabilizing agent in many processed foods, as well as other consumer products such as cosmetics and health-care items. Protists called diatoms have an unusual use. Diatoms are aquatic protists whose shells are made of the chemical compound silica. When diatoms die, their sharp, glassy silica shells fall to the bottom of lakes and oceans, creating large deposits of soil rich in their shells. These deposits are called diatomaceous earth because they are full of the shells of diatoms. Gardeners apply diatomaceous earth to their gardens to keep pests such as slugs out of their gardens. The sharp edges of the shells cut the slugs' soft bodies, which kills them.

Insects obtain oxygen through spiracles, which are small abdominal holes. How Insects Obtain Oxygen In an insect, holes called spiracles, which are located along the abdomen, bring air into the body. An extensive system of tracheal tubes, called tracheae, brings air into the insect's body. The tracheae end in smaller tubes called tracheoles, which reach to all body cells to allow the oxygen to diffuse into the cells. Air travels back down the tracheae, carrying away gaseous waste to the outside of the insect's body.

Imagine that you discover a grasshopper sitting on the edge of your desk. The creature hops around, evading your attempts to catch it for release outside. Grasshoppers, flies, and other insects do not breathe through their mouths. Oxygen is obtained through small holes in the sides of their abdomens called spiracles. Spiracles lead into tracheal tubes called tracheae that branch out into smaller tubes called tracheoles. From there, oxygen diffuses into body cells.

Many protists cause significant diseases in humans and other animals.

In April 1993, over 400,000 residents of the city of Milwaukee became ill from drinking water that had not been properly treated. Tests confirmed that the city's water supply was tainted by a protist called Cryptosporidium, a parasite that causes diarrhea, stomach cramps, nausea, and vomiting. More recently, numerous people became ill after being exposed to this parasite at a water park in New York State. Numerous other human illnesses are caused by a variety of protists. Perhaps one of the most significant human diseases is one you rarely hear about in the United States, but infects over 300 million people around the world. This disease, called malaria, is caused by a parasitic protist called Plasmodium. Click on the icon to follow this parasitic protist's complete life cycle. Many other parasitic protists have equally complex life cycles, in which they spend part of their life in one type of organism and part of their life in another.

Some animals' digestive systems can process seemingly indigestible materials. Special Adaptation To swallow their prey whole, snakes can unhinge their jaws to take in objects much larger than their head. Anacondas of South America, for example, have been known to swallow whole wild pigs and deer. Owls also eat animals whole. Unable to digest bones, however, owls excrete waste pellets that contain the skeletal components of their victims. Because of this behavior in owls, scientists can easily study the diet of different owl species.

In October 2005, park rangers in the Florida Everglades came upon a scene not likely to have ever been witnessed before—the carcass of an alligator protruding from the carcass of a Burmese python. The python had apparently tried to swallow the alligator whole, but both animals had lost the battle. Not native to North America, Burmese pythons were introduced into the Everglades by humans who released their python pets as they grew too large to live in cages. Like the python, most snakes swallow their prey whole, but how do their digestive systems break down tough skin, scales, and bones? A snake's digestive system contains particularly powerful enzymes. The digestive systems of snakes and other organisms have evolved specific enzymes that can break down the range of foods each kind of organism eats. Missing Metadata The digestive system of a snake has enzymes that break down many parts of its prey. Those parts that cannot be broken down pass out of the snake's body.

An open digestive system has an entrance for food and an exit for wastes. Screwworms: Screwworm flies are native to North, South, and Central America. Many governments, including the US Government, have ongoing programs to control the parasites, which are a serious threat to livestock populations.

In a pasture in Mexico, a lone cow lumbers over to a tree and lies down with difficulty. The concerned rancher walks over to investigate and finds a gaping hole in the cow's leg and a bulging sac of skin next to it. The rancher probes the sac with a stick and hundreds of white, squirming larvae tumble to the ground. Probably starting as a small bite or cut, the wound has become a nursery for the offspring of a female screwworm fly (Cochliomyia hominivorax). The larvae of screwworm flies feast on the live flesh of any warm-blooded animal. They take in food through a mouth and digest it in an internal gut, and then they release waste through a second opening. A complete digestive tube with an entrance and exit is called an open digestive system. Open digestive systems are typical of complex organisms, including humans.

In the lysogenic cycle, the virus's genetic material is copied each time the cell divides.

In some viruses, reproduction also involves the lysogenic cycle. In the lysogenic cycle, a virus injects its DNA into a cell, and the DNA becomes a part of that cell's genome. When the host cell replicates its DNA and divides, it also replicates the viral DNA. The viral DNA will be found in all new cells being created. Depending on the virus, the viral DNA may not become active for many years. It is almost as if the viral DNA is asleep. Eventually, when the conditions are right, the viral DNA in the genome is turned on. The cell switches over to the lytic cycle and starts building viruses. Eventually the cell bursts and dies, and the virus particles float away. There are viruses that infect all types of cells. As scientists work to develop vacines, new resistant viral strains develop as virual DNA mutates.

In the lungs, oxygen transfers from the respiratory system to the circulatory system. Text Version Gas Exchange Positioned in the center of the space is a diagram of a small circular portion of a lung. Short lengths of lines surround the circular portion. The lines are labeled, red blood cells. In the center of the portion is a diagram of an alveolus. The alveolus is represented as a small bulb-like structure that looks something like a sphere with a narrow neck at the top. A cross-section of a capillary runs along the outside of the alveolus and parallels the shape of the alveolus. In cross-section, the capillary resembles a tube. It consists of upper and lower walls and space between the walls. The capillary walls are depicted as small oval-shaped structures that touch end to end. These structures are cells. In the center of each cell is a black dot, perhaps representing the nucleus. The space within the capillary, between the capillary walls, contains many tiny light dots. Positioned in the upper right of the space is a key to the diagram. The key consists of two equilateral triangles, one above the other. The upper triangle is light. It is labeled, oxygen. The lower triangle is dark. It is labeled, carbon dioxide. Oval shapes that represent blood cells flow into the capillary from the right. The cells flow leftward through the capillary and out, presumably to a larger blood vessel. When the blood cells enter the capillary on the right, they are dark, which means they are rich in carbon dioxide. As the blood cells pass through the capillary, they become light, which means they are rich in oxygen. At the same time, dark triangles that represent carbon dioxide pass into the alveolus and move upward toward the neck of the alveolus. Similarly, light triangles that represent oxygen pass downward through the alveolus and into the capillary. A caption below the presentation: Oxygen moves into your bloodstream and carbon dioxide moves out.

In the alveoli, an important exchange takes place. Surrounding the alveoli are capillaries—tiny blood vessels so small that molecules can diffuse through their membranes. The outer layer of the alveoli is also permeable. Watch gas exchange take place in the animation at right. Oxygen diffuses from the alveoli in the respiratory system into the capillaries of the circulatory system Opens in modal popup window . In the bloodstream,oxygen binds to the hemoglobin protein complex in red blood cells. Carbon dioxide diffuses out of the capillaries and into the alveoli. From the alveoli, carbon dioxide eventually leaves the body as you exhale. Follow the oxygen-rich blood cells leaving the left side of the animation. Capillaries merge into larger and larger blood vessels called arteries. Arteries Opens in modal popup window carry oxygen-rich blood to the heart and eventually to all of your body cells.

Scientists only recently began to divide life into domains.

In the late 1970s, biologist Carl Woese at the University of Illinois began looking at prokaryotes—single-cell organisms that lack a nucleus. For hundreds of years, scientists grouped all prokaryotes in a single kingdom because of their lack of a nucleus. But Woese began to study the RNA sequences of prokaryotes, and to the surprise of many scientists, he suggested that prokaryotes should be divided into two very distinct categories. Before Woese's discoveries, the kingdom was considered the highest taxonomic category, and all life was classified into just five kingdoms: animals, plants, fungi, protists (eukaryotic, single-cell organisms), and monera, which included all prokaryotes on earth. Woese proposed a new type of tree of life that split organisms into three domains. Woese also divided organisms in those domains into 23 different kingdom-level categories. He based this new classification scheme on new molecular evidence showing the similarities and differences between groups of organisms. Turn to pages 128-129 of your reference book for more information.

Modern classification began with the Swedish botanist Carolus Linnaeus in the mid-1700s. Carolus Linnaeus created a way of classifying organisms that people continue to use today.

In the mid-1700s, Swedish botanist Carolus Linnaeus Opens in modal popup window finally brought some order to the system of naming organisms. He proposed a system by which every organism on earth would have a unique, two-part name—in much the same way that most people have a unique combination of first and last names. In Linnaeus's system, organisms are given their two-part descriptive name in Latin, the language universally accepted for scientific naming. This system of naming things by two names is called bionomial nomenclature. Under Linnaeus's system, every organism's first name identifies the genus it belongs to. Its last name identifies a specific type of organism within the group, known as a species, which is its specific epithet or descriptor.

Historically, taxonomists used physical structures as key characteristics in classifying organisms. Although all birds belong in the class or group named Aves, they are placed in different subgroups depending on beak size and shape, leg type, plumage, and other characteristics.

In the past, scientists classified organisms based on their physical characteristics. For example, the flamingo is classified into groups based on its long legs, long beak, and large body. A duck belongs to the same class as a flamingo—Aves, which includes all birds. But based on physical differences between the two birds, scientists long ago classified ducks and flamingos in different subgroups.

Dangerous Blooms

In the summer of 2005, a federal agency declared a public health emergency in the waters off the coast of New England. The culprit? A type of marine protist that produces a potent toxin, which can paralyze or even kill people who eat it. The protist bloomed, or reproduced, to huge proportions in the coastal waters near New England—an event called a harmful algal bloom. When marine animals such as clams and mussels eat these protists, the toxins build up in their tissues, posing a serious risk to people who eat clams and mussels. For this reason, fishermen were ordered to stop harvesting clams and mussels until the bloom ended.

Bacteria make up one large, prokaryotic domain.

It's hard to find a place on earth that isn't home to at least one species of bacteria. Scientists have divided Domain Bacteria into several broad groups, as you can see on page 132 of your reference book. One way of classifying bacteria into groups considers how they obtain energy. Autotrophic Opens in modal popup window bacteria make their own energy, either through photosynthesis or through chemosynthesis, a process in which bacteria use chemical elements such as sulfur and nitrogen to generate energy. Heterotrophic Opens in modal popup window bacteria break down organic matter in the environment-in other words, they must break down material produced by other living organisms to produce their own energy.

Plant infections

It's not only humans who fall ill from fungal diseases. Fungi also are significant plant pests and can cause significant damage to crops. The Irish Potato Famine, for example, was caused by a fungus that devastated the Irish potato crop in the mid-1800s. Some other plant diseases caused by fungi include Dutch elm disease, sudden oak death, and downy mildew (infects grapes).

Animals are multicellular, eukaryotic heterotrophs without cell walls.

Kingdom Animalia includes many diverse species that live on land, in freshwater lakes and ponds, in the ocean, and even inside the bodies of other animals. They may look very different from one another, but all animals share a basic set of characteristics. They are multicellular and eukaryotic. They are heterotrophic. They lack cell walls. They are capable of sexual reproduction.

3.11 Digestion Organisms must break down the food they ingest before their bodies can generate the chemicals and energy necessary for life. The processing of food is called digestion. Digestion breaks down food into various nutrients. Glucose is sent to cells for ATP production

Leaping toward a blade of grass, a grasshopper never reaches its goal. Its last view of the world is the fangs of the spider that snared it. For the spider, digestion begins before it even takes a bite, when it regurgitates digestive juices onto the grasshopper to soften the hard body parts.

3.12 Digestion in Humans Human digestion is the process that breaks down food both physically and chemically so that the body can absorb needed compounds. The human digestive system breaks down food physically in the mouth, stomach, and intestines, and chemically with many enzymes.

Leaping toward a blade of grass, a grasshopper never reaches its goal. Its last view of the world is the fangs of the spider that snared it. For the spider, digestion begins before it even takes a bite, when it regurgitates digestive juices onto the grasshopper to soften the hard body parts.

Archaeans at a Black Smoker Vent

Learn about a single-cell organism that is uniquely adapted to survive in hydrothermal vents; in this case the vent is located at a depth of more than 2000 meters in the ocean.

People rely on plants in every aspect of their daily life.

Life as you know it simply would not exist without plants. Plants are producers, or organisms that convert carbon and water into the carbohydrates you eat. Plants are photosynthetic and produce much of the oxygen that's in the atmosphere. Plants provide much of your food and many spices used in cooking, such as cinnamon, vanilla, and nutmeg. They provide lumber for building homes and furniture, and can be used as a source of energy to power vehicles and heat homes. Many of the clothes you wear come from plants as well: Cotton is a fiber spun from the cotton plant, and the indigo dye that puts the blue in your jeans comes from a plant, too. This large kingdom of living organisms provides the foundation for animal life on land. Missing Metadata Without plants, animal life as you know it would not exist.

The human digestive system contains many parts that break down food physically and chemically. Pizza: Pizza can actually be a healthful meal when it includes most of the major food groups-grains, fats, vegetables, dairy products, and meat.

Moments after paying the pizza delivery person, you pull the steaming box open. Manners and plates left aside, everyone grabs an oozing slice and bites into the familiar triangular shape. Regardless of the type of food a human eats, the digestive process is always the same: The human digestive system, with its many organs, breaks down food physically and chemically to distribute nutrients to all parts of the body. But what exactly happens to a piece of pizza as it moves through your digestive system? Missing Metadata No matter what kind of food a human eats, the digestive process is the same.

3.17 Obtaining Oxygen The production of energy in almost all living things depends on a consistent supply of oxygen. Organisms obtain oxygen in various ways. Organisms obtain oxygen through diffusion, absorption, inhalation, and pores.

Nearly every living thing on earth requires a steady supply of oxygen to survive because it is needed for cellular respiration. To get their critical oxygen, organisms have evolved different mechanisms for doing so. Not surprisingly, less complex organisms have less complex ways of obtaining oxygen, while more complex organisms have more complex ways.

Humans remove gaseous, liquid, and solid waste, each through its own organ system. Human Waste: Gas (such as Co2) leaves via lungs, mouth, and nose. Liquid (urine) leaves via liver, kidneys, and bladder. Solid (feces) leaves via the colon, rectum, and anus.

No, this is not a joke. Today, you're going to learn about your waste products and how your body gets rid of them. Human beings, all other mammals, and many other animals share similar waste removal systems. Separate systems work on gaseous, liquid, and solid waste.

Waste Water Treatment

Now you will watch a video to see the process of waste-water treatment that removes most but not all pollutants before returning the water back to the rivers. Transcript (Video with Audio Description) Screen 1: 00:00:00.00 Description: Shown is a water treatment facility. There are many large circular structures in the ground, filled with water. A multi-paddle strainer rotates through the top of the water. There is a large circular tank. Along the top, water filters out between metal pieces and goes down a drain. 00:00:22.00 Female Narrator: Water from washing machines, toilets, sinks, and storm drains all ends up here. First the big bits of rubbish are sieved out and thrown away. Then the finer particles are left to settle out at the bottom of huge tanks, while the water drains off at the top. 00:00:50.00 Description: Large metal rotating pipes spray water as they move over rocks. 00:00:57.00 Female Narrator: Finally, it's trickled over stones holding tiny plants, insects, and bacteria. Between them, they digest most of the organic matter. 00:01:12.00 Description: A man lowers a bucket attached to a long pole into a cement pipe in the ground. There is water flowing at the bottom. He pours the water into a long glass cylinder. The water is clear. 00:01:26.00 Female Narrator: So, by the time it comes out again, the water is fairly clean. It's checked to see how clear it is, but some of the pollutants you can't see are the phosphates from detergents. They're still dissolved in the water, and the companies say it's too expensive to remove them. 00:01:46.00 Description: Water flows from a tunnel to a river. Large amounts of brown algae grow on the floor and the plants in the river. 00:01:55.00 Female Narrator: But released into the river, phosphates act as a fertilizer to these brown algae. They grow on top of the normal water weeds and smother it, especially when the river is not flowing fast enough to clear it away. 00:02:12.00 Description: There is a series of images: A pond with two cows nearby, a hillside with cows, a field with pigs. There is a river with a field in the background, then a close-up of the river. There is a buildup of brown algae being pushed up against a blockage in the river. 00:02:32.00 Female Narrator: Farming is a source of phosphates and nitrates, too, as pesticides and fertilizers run off into the river from nearby fields. Even the free-range pig units produce a huge amount of ammonia. All of these inputs are polluting the river and fertilizing the brown algae, and they build up where the water is stagnant. Ending Time: 00:02:53.00

The end products of digestion are glucose and other chemical compounds.

Organisms eat to obtain energy and materials to build cells and body structures. Once the digestive system breaks down the food, nutrients are transported to the cells of the body. Roll over the buttons on the image in numerical order to follow the steps of human digestion. Sometimes organisms use nutrients intact. Other times they use chemical compounds from the food. For example, organisms use amino acids for building proteins. But because all organisms need glucose to produce ATP during cellular respiration, glucose in particular is generated in large amounts during digestion.

Organisms make or seek out sources of energy.

Organisms fall into one of two categories depending on how they obtain energy. Autotrophs Opens in modal popup window are organisms that make their own energy. Plants are autotrophs.They take in energy from sunlight and use it—along with water and carbon dioxide—to make glucose. Heterotrophs Opens in modal popup window are organisms that seek out and eat other organisms. Animals are heterotrophs.

Humans obtain oxygen through the respiratory system. The circulatory system distributes the blood to all cells.

Oxygen enters the lungs, all the way to the alveoli. Capillaries surround the alveoli, and oxygen enters them by diffusion. Oxygen binds to hemoglobin, and blood carries it to the heart. The heart pumps blood to the rest of the body, traveling through arteries. Eventually, the arteries narrow into another set of capillaries that interface with body cells. Oxygen leaves the capillaries through diffusion, enters cells, and is used in cellular respiration. The process reverses itself to remove carbon dioxide from your body.

Bacteria can be helpful as well as harmful.

People tend to associate bacteria with illness. They're not wrong: Streptococcal bacteria destroy red blood cells, and the bacteria that cause the disease tuberculosis break down lung tissue and use it as a source of energy. Here are some significant human diseases caused by various species of bacteria. Have you heard of any of them? They frequently make news headlines. Harmful Bacteria Opens in modal popup window However, it's important to know that not all bacteria cause disease. Many bacteria play helpful roles in ecosystems, food processing, and your body's digestive system. Bacteria help turn milk into yogurt and cheese. Other bacteria break down dead or decaying organisms on the forest floor. And if it weren't for bacteria, you'd have a hard time digesting many foods. Bacteria that live in your large intestine help break down many types of carbohydrates during digestion. The list of beneficial bacteria is very long.

Plants share several basic characteristics.

Plants all belong to Kingdom Plantae in Domain Eukarya, as you can see in the phylogenetic tree on pages 130-131 of your reference book. But what are the defining characteristics of a plant? Scientists use a few characteristics to classify plants into the lineages on page 136 of your reference book. Plants are multicellular. They are eukaryotic. They are photosynthetic. Plants have a covering called a cuticle, which helps prevent water loss. Most plants have stomata, specialized openings in their surface cells that permit gas exchange.

Plants obtain energy from the sun.

Plants obtain energy from the sun. In the dense shade of an equatorial rain forest, a tree fern competes for sunlight. Each frond of the fern acts as a solar panel, angling in the best direction to catch the rays of the sun. The ability of the fern to lean toward sunlight—a characteristic called tropism—gives the fern a fighting chance at survival in the dim light of the rain forest floor. Once the sunlight reaches the leaves of the fern, the process of photosynthesis Opens in modal popup window kicks in and produces molecules of glucose in large quantities. This energy—light energy that becomes chemical energy—is what ferns and most other autotrophs, such as these sunflowers, need to live. Missing Metadata Through photosynthesis, plants transfer the energy in sunlight to a form of energy that they can use.

Protists and fungi are two diverse groups of eukaryotes.

Protists and fungi are two groups of organisms that you probably don't think about much, but they play important roles in ecosystems, are used in many consumer products, and can cause significant diseases. Protists are a very diverse group of eukaryotes that includes several distinct evolutionary lines. Fungi, however, have a single common ancestor and share several basic characteristics.

The broadest, most inclusive grouping of life on earth is the domain. All life is classified into one of three domains. Phylum equals Division. When talking about plants, scientists often use the term division rather than phylum. Ex. 1 Domain Eukarya (all eukaryotes) Kingdom Animalia (all animals) Phylum Chordata (all vertebrates) Class Mammalia (all mammals) Order Carnivora (includes cats, dogs, bears, etc) Family Felidae (cats) Genus Puma (lion) Specific Ephithet concolor (having one color) ex.2 Domain Eukarya (all eukaryotes) Kingdom Plantae (all plants) Phylum Magnoliophyta (all flowering plants) Class Magnoliopsida (all dicotyledons) Order Caryophyllales (includes amarynths, pinks, and pokeweeds) Family Cactaceae (all succulents) Genus Carnegiea (one genus of cactus) Specific gigantia (gigantic)

Scientists today organize all life on earth into three very broad categories called domains. Organisms are classified into one of three domains based on very fundamental characteristics, such as what type of cells they are made of, how they get food, and what their cell chemistry is like. Within each domain, organisms are further classified into groups called kingdoms based on similarities—in other words, each domain includes several kingdoms of related species. And, within each kingdom, living things are further subdivided into smaller and smaller groups—phylum, class, order, family, genus, and specific epithet-based on similarities. Each group becomes smaller in number.

Feces collect in the rectum, the final portion of the large intestine. Feces excrete through the anus. Keeping it Clean Because feces carry many types of bacteria capable of causing disease, animals, including humans, make sure the anal area is cleaned.

Solid waste leaves the body as feces Opens in modal popup window . Feces-compacted and ready for excretion-enter the final part of the large intestine called the rectum. As in the urinary bladder, two sphincter muscles hold the feces in the rectum until the time comes for excretion: Similarly, one is involuntarily held, and the other you control. Once the body is cued that it needs to dispose of its solid waste, the muscles expel it through a hole called the anus. There is a diverse population of bacteria inhabiting your intestines. Each bacterium digests certain foods and produces distinctive, foul-smelling odors as its waste product, which becomes part of yours. Some of these chemicals are ammonia or sulfides that are really noxious smelling. The scientific word for expelling feces is defecation.

Some organisms also excrete gaseous waste through the respiratory system.

Solid, liquid, gas—the three states of matter...or the three states of waste? Just as organisms need to rid themselves of liquid and solid waste to keep proper balance and homeostasis, organisms must also do so with gaseous waste. For plants, gaseous waste from photosynthesis is oxygen. Don't forget, plants also undergo respiration and therefore have some carbon dioxide gas waste as well. All gaseous waste in a plant exits from small openings in leaves, or stomata Opens in modal popup window . In animals, the main gaseous waste is carbon dioxide from respiration. A variety of mechanisms to dispel carbon dioxide exist, from simple diffusion out of cells to dissolving it in water, to the familiar exhalation seen in most animals. In the flatworm, no formal respiratory system exists. Gases simply diffuse into and out of its cells.

Many organisms, including the flatworm, have a closed digestive system. Sea Stars: The sea star is another organism that has a closed digestive system. Instead of capturing food with a pharynx like the flatworm, however, the sea star turns its stomach inside out and throws it over its prey.

Some animals, such as the flatworm, have a closed digestive system. A closed digestive system has only one opening. Food comes in and waste goes out through the same opening—a mouth at the end of an organ called a pharynx. The flatworm can extend its muscular pharynx Opens in modal popup window to catch prey. Strangely enough, the pharynx is located in the middle of the flatworm, not near the head where you would expect to find it. After pinning its prey with the pharynx, the flatworm begins the process of digestion by excreting digestive fluids onto the prey from its mouth. The fluids dissolve the prey's body so the flatworm can ingest it more easily. Explore how flatworms eat. Feeding and Digestion in Platyhelminthes. http://shapeoflife.org/video/flatworm-animation-body-plan

Fish absorb dissolved oxygen from water through gills. How Fish Obtain Oxygen In fish, the gills are located around openings in the body so the water can be made to flow over the gills in one direction. Water flows into the fish's mouth and through gill filaments, where the capillaries are located close to the surface to allow gas exchange. Water flows out the gill opening.

Swimming silently through lakes, streams, and oceans, fish don't seem to need anything from anyone. Yet, despite their apparently carefree appearance, without oxygen, just like all organisms, fish would quickly perish. So, how do fish breathe underwater? Do they break down water molecules and get oxygen that way? It might seem logical, but it actually isn't true. Oxygen gas (O2), like that you breathe, is dissolved in water—it is a mixture. Fish absorb the dissolved oxygen through gills. Gills are often described like fans or feathers, and they extract dissolved oxygen gas from the surrounding water as it passes over them.

The human lungs are the locations for gas exchange with air.

Take a deep breath. Doesn't it feel like the air just spreads out from your lungs into your body? In reality,the process is not this random. A cell's existence depends on the controlled movement of gases through the respiratory system Opens in modal popup window . Oxygen doesn't simply flow into your cells as you take breaths-instead, it is delivered. The mouth and nose are the only two entryways available to bring oxygen into the body. Next, oxygen travels down your throat in a pipe called the trachea. The trachea splits into two branches, or bronchi, which each lead into a lung. The bronchi branch over and over again. Each time, the diameter of the airway narrows. Each time, the new branch has a new name, until the final branch leads into a cluster of tiny air sacs called alveoli. Each lung is made up of these numerous branches which end at an alveolus. Alveoli Opens in modal popup window look like spongy little sacs. Lungs are largely made up of alveoli—over 350 million of them. Turn to page 158 of your reference book for another look at the respiratory system. Also explore the human respiratory system in the online activity.

The teeth of omnivores are shaped to eat many kinds of food. A Balanced Diet Even though humans can eat both plants and animals, they require a certain balance of nutrients. Eating only meat, for example, is unhealthy for humans. A mixture of plants and animals seems to be the right combination, with a greater emphasis on plant than animal sources of energy.

Take a moment to look at your teeth in a mirror. Do you see that your teeth have many different shapes? They are shaped that way for a purpose. The flat molars can grind up leaves and crunchy vegetables. The pointy canines and sharp incisors can tear meat into pieces. Humans have the ability and the anatomy to eat many types of food. But whatever the meal, humans the world over must eat nearly every day. Unlike an anaconda or a crocodile, which can go for many months without eating, or a bear that hibernates through the winter, humans must eat frequently to stay healthy. Missing Metadata Human teeth are shaped to chew both meat and plants.

Biologists arrange organisms into a hierarchy of groups and subgroups based on similarities and differences. There are almost 1.8 million named species on earth, and there may be as many as 5 to 40 million more. But how can you make sense of all these species? Well before the 1750s—the Age of Linnaeus—scientists made observations of the natural world and classified the organisms in it based on similarities and differences. Since Carolus Linnaeus, the science of taxonomy has grown into a field that helps scientists categorize all life on earth.

Taxonomy groups organisms by similarities and differences in physical characteristics and DNA structure

Biologists arrange organisms into a hierarchy of groups and subgroups based on similarities and differences.

Taxonomy is the science of classification, the process that groups organisms into categories and subcategories based on similarities and differences. Historically, scientists relied on physical structures to group different organisms. Today, scientists also rely on evidence from comparative DNA and molecular biology to strengthen existing classification schemes and sometimes produce new ones.

The Digestive System Choking A piece of cartilage called the epiglottis normally covers a person's trachea (air tube) to keep food from going down the wrong way. Choking occurs when food gets into the trachea and blocks the flow of air. If the person can cough, he or she can most likely get the food out by continuing to cough. But a person who is choking cannot breathe, cough, or make any sounds, and may require a first aid technique called the Heimlich maneuver to dislodge the blockage. Sphincters Your digestive system has a series of valves called sphincters that play a role in the passage of food and liquids. They are located between the esophagus and stomach, between the stomach and small intestine, between the small intestine and large intestine, and at the anus. When each sphincter is closed, it keeps material from passing on to the next organ, giving the organ a chance to do its job.

The Digestive System Regardless of what type of food a human eats, the digestive process is always the same. The human digestive system with its many organs breaks down food physically and chemically to distribute nutrients to all parts of the body. What exactly happens to food when it enters your digestive system? Mouth, Pharynx, and Esophagus The first step in digestion takes place in the mouth. As your teeth chew the food into small pieces, glands in your mouth secrete saliva—a watery substance that has two main functions: It lubricates the food so you can swallow, and it contains amylase—an enzyme that begins the chemical breakdown of the carbohydrates in the food. After you've chewed the food into small pieces, you're ready to swallow. With the aid of your tongue, you force the food into the back of your mouth into the pharynx, where the swallowing reflex kicks in. Next, the food enters the esophagus—a muscular tube about 25 cm long that is connected to the stomach. The muscles of the esophagus contract and squeeze the food downward. The repeated contractions are known as peristalsis. Stomach (Physical Action) After being squeezed down your esophagus, the chewed-up food enters your stomach. A muscular, saclike organ, the stomach contracts in a manner similar to that of the esophagus. The food is beaten to a pulp by the movements of the stomach muscles, and becomes completely unrecognizable as your stomach churns and mashes it for 2 to 6 hours. Stomach (Chemical Action) The stomach is also the site of chemical digestion. Cells in the stomach wall secrete an acidic blend of gastric juice, which has two main components: hydrochloric acid (HCl) and pepsin. Both are involved in the chemical breakdown of proteins. The stomach produces about 2 liters of HCl each day. Why doesn't all that acid burn holes in your stomach? The lining of your stomach is covered with mucus through which the acid cannot burn. In addition, fluid called bicarbonate is released after a round of digestion to neutralize the acid. Bicarbonate is a base, and bases function in opposition to acids. Small Intestine, Liver, Pancreas, and Gallbladder Once the stomach has pulverized the food, the partially digested mass enters a long, coiled tube called the small intestine, or duodenum. The word small refers only to the diameter of the small intestine compared with that of the large intestine. The length of the small intestine is impressive: It is nearly 7 meters (20 feet) long—longer than a car. Connected to the first part of the small intestine are three different organs—the pancreas, the liver, and the gallbladder. Each plays a role in supplying enzymes that aid in the digestion of food. The liver manufactures bile salts that break down fats. The gallbladder stores bile from the liver and releases it as needed. The pancreas produces enzymes that break down carbohydrates, proteins, fats, and nucleic acids. Small Intestine (Villi) Your food is now almost fully digested. Many food molecules are ready to make their way to the body cells. Much of that transfer occurs at special structures that line the wall of the small intestine. The inner surface of the small intestine is covered with millions of villi—tiny extensions that look like little fingers. The villi trap molecules of the digested food pulp as it moves through the small intestine. Inside the villi are capillaries—blood vessels that are connected to the veins and arteries of the circulatory system. Food molecules move from the small intestine into the capillaries, and then into the bloodstream. Liver The capillaries in the villi move the food molecules into the bloodstream, and the blood then moves through the liver for one last digestive effort. As nutrient-packed blood enters the liver, several things happen. Extra sugar in the food is stored in the liver as glycogen, and when the body needs more energy, the glycogen can be broken down into glucose. Toxins are filtered from the blood and are either broken down or stored in the liver. Amino acids are altered into forms that the body needs. Certain vitamins and iron are stored in the liver. After passing through the liver, the food molecules are carried through the bloodstream to all body cells to supply nutrients and the glucose they need for cellular respiration and the production of ATP. Large Intestine What happens to the leftover material that didn't pass into the bloodstream from the small intestine? It enters the large intestine. The large intestine is much shorter than the small intestine, but it has a larger diameter and is not coiled up. The main function of the large intestine is to absorb any remaining minerals and water in the waste of digestion. The large intestine also harbors colonies of bacteria that produce several compounds that the body cannot make on its own, such as vitamin K and many types of B vitamins. The bacteria also help compress the indigestible materials into solid waste called feces, which eventually exit the body through the rectum and anus.

Throughout history, people have grouped organisms into categories based on similarities and differences. Although flawed, Aristotle's classification of life on earth influenced scientific thought for centuries.

The Greek philosopher Aristotle, who lived from 384-322 B.C., was an astute observer of the natural world. He developed a classification scheme that organized life on earth into several categories. First, he split life on earth into two groups: plants and animals. Then, he further divided animals into two groups: animals with red blood and animals without red blood. He further divided these groups into smaller categories, such as shelled animals, fish, and birds. A key point is that Aristotle based his classification on the physical features he observed in those organisms, and he also grouped animals according to how they moved: flying, swimming, or walking. Aristotle's original classification scheme wasn't without error—for instance, he called animals such as jellyfish and corals zoophytes, meaning animal-plant. They were neither animal nor plant but had characteristics of both groups. Plus, classification by type of movement could place bats and birds in the same category. Still, his writing about the natural world influenced the way people understood living things for hundreds of years.

One species of archaean made possible much of the DNA revolution.

The archaean species Thermus aquaticus, which lives in hot springs at temperatures near the boiling point of water, has become very important to molecular biologists around the world. This species produces an enzyme called polymerase. Polymerase is an enzyme that all species rely on for DNA replication. Most polymerase enzymes cannot tolerate high temperatures, but the polymerase found in T. aquaticus can. For this reason, scientists use this polymerase in the chemical process PCR (polymerase chain reaction). PCR produces thousands of copies of a DNA strand in a short time, and these copies have many uses in biotechnology. The process requires both high temperatures and a polymerase that won't degrade at those temperatures. The discovery of the polymerase in T. aquaticus, called Taq polymerase, opened the door to many advances in DNA research.

All living things require an external source of energy.

The diversity of life on the planet is vast. If there is one thing that ties the different organisms together, it is that they all need energy to survive. An eagle circling a rabbit's den, a tiger stalking a wild pig, and even a water lily soaking up the sun's rays—all forms of life need a consistent source of energy.

Carnivorous heterotrophs, such as flatworms, seek out and consume meat.

The flatworm is a tiny organism with an extremely small mouth and, needless to say, a flat body. To take in energy, this small animal has evolved an ability to liquefy the solid parts of animal bodies, which it can then more easily convert to usable chemical energy. The flatworm has an unusual way of eating, but it is no different from other carnivores in that its source of chemical energy is other animals. Missing Metadata Flatworms are carnivorous heterotrophs.

Organisms use cellular respiration to make usable energy.

The food an organism ingests is not instant energy. All of the different kinds of molecules—fats, carbohydrates, proteins, nucleic acids—are important, but at some point an organism's body must transfer the energy stored in those molecules into ATP Opens in modal popup window , the energy that cells can use. Recall that during cellular respiration, cells transfer the energy in glucose to the energy in ATP. Each cell must make its own ATP; to do so, it needs the starting component of glucose.

Human digestion physically and chemically breaks down food.

The food that a human eats contains vital compounds that a person needs to stay healthy. But those compounds need to be released from the food and transferred into the body cells. Several body parts, including the mouth, esophagus, stomach, small intestine, and liver actively work to break down food and make those compounds available to the rest of the body. It is in the small intestine specifically that food molecules enter into the bloodstream and can then move throughout the body. The large intestine helps rid the body of undigested materials and waste products.

Living things depend on oxygen for cellular respiration. Mechanisms of obtaining oxygen vary among groups of organisms.

The mechanisms to obtain oxygen vary, depending on the complexity of the organism: diffusion: prokaryotes and simple organisms, such as the flatworm pore entry: plants and insects absorption by gills: fish inhalation through lungs: reptiles, birds, and mammals Nearly every living thing depends on oxygen to live, because it is used during cellular respiration to produce ATP, the energy that cells use for all functions.

Two major plant lineages include plants that produce seeds. Cherry trees are angiosperms that produce flowers every spring. The flower ovaries develop into fruit. Tulips are angiosperms with a single large flower. Pine trees are gymnosperms and produce seeds in cones. Cycads are gymnosperms that produce seeds most often in cones.

The next two lineages of plants have several structures that make them even less dependent on water: gymnosperms, which include pine trees, cycads, and cedar trees, and angiosperms, which include all plants that produce flowers, from grasses to roses to maple trees. Turn to pages 136-137 of your reference book for several examples. What does the phylogenetic tree on page 136 tell you about the evolutionary history of these two groups? Gymnosperms and angiosperms both produce pollen, which is a tough protective coating surrounding sperm cells. Pollen resists drying out-for this reason, it's a huge step toward solving the challenge of living on land. It can be carried between plants by wind currents or animals. Gymnosperms and angiosperms also produce seeds, or structures that protect and nourish a growing plant embryo. Seeds Opens in modal popup window help resist drying out, freezing, fires, and even the digestive enzymes produced by animals.

Viruses reproduce inside the cells of living organisms.

The next two screens look at a T4 bacteriophage. As the name implies, bacteriophages infect bacteria. Viruses cannot manufacture their own proteins, and they must rely on the living cell of another organism to reproduce. Viruses reproduce in one of two different ways: the lytic cycle and the lysogenic cycle. In the lytic cycle, a virus infects a cell by injecting its DNA (or RNA) into the cell. The cell's DNA replication machinery-enzymes and other proteins-replicate the viral genes and produce the proteins required to make the capsid, or protein coat of the virus. The viral DNA directs the living cell to assemble new viral particles. Ultimately, the cell bursts open, releasing new viruses. The new viruses can go on and infect new cells.

Domain Eukarya includes all organisms made of eukaryotic cells.

The organisms with which you're probably most familiar—the mushrooms that sprout up after a summer rainfall, the fruits you eat, the animals you see at the zoo, the mosquitoes that bite you in the summertime—all belong to Domain Eukarya, the taxonomic group containing all organisms composed of eukaryotic cells. Later in this unit, you'll learn more about some of the more familiar groups of eukaryotes: protists, fungi, plants, and animals. Keep in mind, however, that you'll only survey a fraction of the diversity of life on earth. Pages 134-139 of your reference book highlight some major types of organisms that fit in Domain Eukarya.

Different organisms carry out similar life functions in different ways.

The organisms you've been learning about—from the archaeans living in hot springs to the animals living in Antarctica—need to obtain energy to carry out their life functions. They carry out their life functions in very different ways, depending on where the organisms live or what processes they use to obtain energy. Scientists call this collection of characteristics—how organisms obtain energy, how they reproduce, and where they live—a life history. A life history provides a context that helps scientists better understand how an organism functions and how it evolved. The life history of a sea otter, for example, involves living on the coast, giving birth to live young, and obtaining energy by hunting many marine animals such as sea urchins and crabs. Missing Metadata Sea otters have a very specific life history.

Newly oxygenated blood travels to the heart to be pumped to the rest of the body. Arteries and Veins: The circulatory system consists of the heart and the blood vessels—arteries and veins. Arteries carry oxygenated blood. Veins carry deoxygenated blood. Arteries are often colored red because oxygenated blood is more of a red color. Veins are often colored blue because deoxygenated blood is more of a blue color. If you accidently cut yourself, and your blood is exposed to air, your blood immediately turns bright red because of the oxygen in air. Text Version Heart-Lung Cycle Positioned in the center of the space is a diagram of the heart, lung capillaries, and body capillaries. Positioned above the heart are the lung capillaries. Positioned below the heart are the body capillaries. The capillaries are represented by net-like structures. The right side of the heart is dark. A dark path-like structure, labeled artery, connects the right side of the heart to the right side of the lung capillaries. A second dark path-like structure connects the right side of the heart to the right side of the body capillaries. The left side of the heart is light. A light path-like structure, labeled vein, connects the left side of the heart to the left side of the lung capillaries. A second light path-like structure connects the left side of the heart to the left side of the body capillaries. The part of the lung and body capillaries on the right are dark and correspond with the dark part of the heart. The capillaries change gradually from dark on the right to light on the left. A system of arrows highlights in sequence. The sequence shows the flow of blood through the body. The flow is as follows: Arrows show that blood flows from the right side of the lung capillaries down to the right side of the heart. Arrows show that blood flows through the heart and then up, around, and down through the artery to the body capillaries. Blood flows through the body capillaries from right to left, to the vein that carries the blood up to the left side of the heart. From the left side of the heart, arrows show that blood flows up and around to the left side of the lung capillaries. Blood moves from the left side of the lung capillaries to the right side where it becomes dark. From there the cycle begins again, with blood flowing to the right side of the heart.

The oxygenated blood from the capillaries flows into merging arteries that all lead to the heart. The purpose of the heart is to pump the blood and keep it moving. The oxygen-rich blood is pumped from the heart to the rest of the body. As the blood travels toward the cells,the arteries branch into smaller and smaller blood vessels. Eventually,the blood once again finds itself in capillaries. However,this time,the capillaries network with cells somewhere in the body. Oxygen then diffuses out of the capillaries and into cells. Once in cells, the oxygen is used in cellular respiration. Oxygen-rich blood flows from the capillaries in the lungs to the capillaries somewhere in the body. Oxygen is picked up in the lung capillaries and delivered in the body capillaries. Check out the diagram on page 159 of your reference book. It is important to remember that the circulatory system pumps the oxygenated blood from the lungs to all parts of your body, but simple diffusion moves the oxygen across cell walls and capillary walls.

Flatworms are simple invertebrates with flat bodies.

The simplest bilateral organism is the flatworm, like the planarian on page 139 of your reference book. As the name suggests, flatworms have flat bodies. They don't have any true organ systems, and they rely on diffusion to deliver oxygen and other gases into and out of their cells. Some flatworms—such as the freshwater flatworm in the photo at right—are free living, but many are parasites that live inside other organisms. Flatworms, such as flukes and tapeworms, can cause serious illnesses in humans and in other animals. In tropical locations around the world, the disease schistosomiasis is caused by flatworms that spend part of their lives inside snails and part of their lives inside humans. The worms can penetrate the skin of people wading in water where the worms live. Once inside a person, they grow inside blood vessels and lay eggs that travel to the bladder or intestines. To learn more about these parasitic flatworms, click here.

Mosses are seedless nonvascular plants. Moss (phylum Bryophyta) grows well in damp, cool environments. Liverworts grow well in damp, cool locations. Hornworts grow in moist environments.

The simplest plants you'll find growing on earth are mosses. Mosses are nonvascular plants, or plants that lack specialized tissues for transporting water and nutrients. Mosses rely on diffusion to move materials into and out of their cells. For this reason, mosses live in moist habitats, and they usually grow close to the ground. Their reproductive cycle requires water, because their sperm cells must swim through water to reach egg cells. Their reproductive cycle does not involve the production of seeds. Mosses also lack true roots, stems, and leaves. Other examples of seedless nonvascular plants include some you might not be too familiar with: liverworts and hornworts. Their names are peculiar, but these little plants are fairly common inhabitants of streambeds and tropical forests.

Kingdom Protista contains a wide variety of single-cell and multicell organisms. Protists are characterized more by their diversity than by their shared characteristics.

The two prokaryotic domains of life are Domain Bacteria and Domain Archaea. The third domain is Doman Eukarya. This domain includes all eukaryotic organisms on earth—that is, all organisms whose cells have a nucleus and membrane-bound organelles. One way for you to think about protists Opens in modal popup window is that they are eukaryotes that are not plants, animals, or fungi. There is not one clear set of characteristics that unifies them. As you will see, protists can be unicellular or multicellular. They may be autotrophic, producing their own food through photosynthesis, or heterotrophic, obtaining energy from other organisms. As scientists learn more about protists, it is likely that they will divide them into several kingdom-level groups.

Every organism can be described taxonomically.

The type of classification scheme that you just walked through for the flamingo can be applied to every organism with a known species name. For example, consider a common tree in the eastern United States, the sugar maple. The sugar maple's species name is Acer saccharum. Based on this information, you can use a classification chart and find out the sugar maple's complete classification: Genus Acer belongs to family Aceraceae, and as you work your way up the classification scheme, you know that sugar maples belong to Kingdom Plantae (plant kingdom). So far, scientists have classified and described over 1.8 million species on earth, but their job is nowhere near complete. They discover new species every year, and they must study and place each species into the correct domain and kingdom before they can determine whether it is indeed a new species, or if it belongs to an already described species.

3.06 Animals are multicell organisms that must consume other organisms. They are made of eukaryotic cells that lack a cell wall.

They look like flowers, but sea anemones are not plants-they are animals. How can something that looks so plantlike be an animal? Like all animals, sea anemones share several basic characteristics: They are heterotrophs, they are multicellular, and their eukaryotic cells do not have a cell wall. Kingdom Animalia belongs to Domain Eukarya. In this lesson, you'll explore the diversity of this kingdom.

3.07 Plants The huge variety of plants on earth is a testament to how living things solve life's challenges. eukaryotic, multicellular, and photosynthetic are plants. Plant types are nonvascular seedless, vascular seedless, and vascular with seeds.

Think about how different your life would be if there were no plants on earth—no maple syrup for pancakes, no wood to build homes, no popcorn at the movies, no french fries to go with your burger, and no bun for that burger. Not even your favorite jeans would exist. The diversity of plants that people depend on came about through millions of years of evolution.

Plants such as ferns spend most of their life anchored in one place.

Think of the plants you know: trees, grass, flowers, and ferns. Can they move about in search of food or mates? No. Adult plants remain anchored in one position, and have evolved a set of characteristics that helps them carry out all their life functions while stuck in one spot. Take a closer look at a fern, which is one of the representative organisms you'll study in depth in the next several lessons. Missing Metadata Bracken ferns are common in many areas of North America.

Plants often store waste inside of leaves. Wastes in Tree Bark Some trees also store wastes in bark.

Throughout time, people the world over have relaxed and slept under the shade of trees. Whether it is to escape the scorching sun or to rest in a comfortable place, humans have found spots worthy of mention in literature for centuries. It's good that plants rid themselves of wastes in different ways than animals. Plants do produce waste in the form of excess ions, and from products of the various cellular processes they carry out. Rather than being routinely excreted, wastes of a plant are stored in the central vacuole Opens in modal popup window of the cell until the time when that cell either dies or that part, such as a leaf, detaches from the plant. The wastes in each vacuole simply fall away when the leaf flutters to the ground. Turn to page 153 of your reference book to read about plant waste.

Transcript: Black Smoker Vent

Transcript (Video) Screen 1: 00:00:00.00 Narrator: Archaea are single-celled organisms similar to bacteria. One species of Archaea is uniquely adapted to survive in hydrothermal vents despite the high temperatures, darkness, extreme pressure, and chemicals that are toxic to most life.

Many animal phyla have bilateral symmetry.

Turn once again to the phylogenetic tree on page 139 of your reference book. Notice the branch labeled "Animals with bilateral symmetry." What does this mean? It means that all animals represented in this branch have an overall body shape in which one side is the mirror image of the other. Why would biologists care about this? It turns out that an animal's body plan and symmetry provide clues about which phylum the animal belongs to and its evolutionary history. Be sure to become familiar with the following body plans: bilateral symmetry Opens in modal popup window , radial symmetry Opens in modal popup window , and asymmetry Opens in modal popup window .

Kidneys filter blood and produce urine by removing urea and other soluble materials.

Turn to pages 154-155 of your reference book for the next few screens. Humans have two kidneys Opens in modal popup window , located on either side of the abdominal cavity. Both are about 12 cm long and are shaped like certain beans-in fact, the bean is named after the organ. Kidneys produce urine Opens in modal popup window . Urine is composed of 95 percent water; 2.5 percent urea; and 2.5 percent other soluble materials such as salts, hormones, minerals, and enzymes. Click the popup button, and then follow along with the diagram as each main part is described: Renal artery brings in blood for filtration. Renal medulla is the part of the kidney where blood branches into smaller arteries and is sent to a filtration area. Renal cortex is the site of filtration, and it contains functional units of the kidney called nephrons. Renal pelvis acts like a funnel to collect urine, and directs it to the bladder via the ureter. Renal vein is how filtered blood leaves the kidney.

Jellies and corals have stinging cells.

Turn to the phylogenetic tree on page 138 of your reference book. The next major lineage includes corals, sea anemones, and jellies. These animals belong to phylum Cnidaria. The word cnidaria comes from the Latin term cnide, or nettle, which is a plant with stinging hairs. Don't be fooled, though—cnidarians are animals, not plants. As the name suggests, cnidarians are animals with specialized stinging structures—cell-sized weapons called nematocysts, or specialized cells that contain a harpoonlike structure and a nerve toxin. The structures help cnidarians immobilize prey. Unfortunately, some cnidarians, such as the box jellyfish, produce toxins that can be life-threatening if people come in contact with them. Structurally, a cnidarian is a fairly simple organism. Its body is made up of two layers of tissue, and inside of its body is a simple digestive cavity.

The prokaryotic domains are Archaea and Bacteria. Viruses are not living things.

Two of the three domains of life include only prokaryotic organisms. These domains—Bacteria and Archaea—are made up of organisms as different from each other as they are from you. While they are microscopic, the organisms in these two domains make up the vast majority of life on earth, and they play many significant roles in human health, the environment, and industry. Viruses are not living, as they are not cellular. They need living cells to help them reproduce.

Taxonomy classifies organisms based on their evolutionary relationships. Look up Finch Taxonomy or refer to your lesson International Code The International Code of Zoological Nomenclature provides a set of guidelines that scientists all over the world adhere to for naming newly discovered animal species.

Unlike earlier classification schemes, modern schemes of classification better show how different organisms are related in a phylogenetic context. Taxonomy helps scientists and others make sense of the natural world. Understanding an organism's phylogenetic history leads to better understanding of earth's past. Taxonomy is a field that continues to grow. Some scientists estimate that as many as 5 to 40 million different species exist on earth, yet less than 2 million of them have been discovered and described. As new species are discovered, taxonomists study how they relate to known species and come up with the proper nomenclature to identify them. Find out how more than a dozen types of Galápagos finches may have evolved from a single ancestor finch.

Many people informally classify animals as either vertebrates or invertebrates.

Vertebrate and invertebrate are two terms you may be familiar with. Vertebrate refers to organisms such as humans, fish, and birds that have an interior skeleton, or endoskeleton, and a backbone. Invertebrate refers to animals such as insects, sea anemones, and worms that lack an interior skeleton. Invertebrates far outnumber vertebrates on earth-in fact, scientists estimate that 75 percent of multicell life on earth belongs to just one invertebrate phylum, Arthropoda. By numbers alone, arthropods rule the earth. You'll learn more about arthropods later in this lesson. Missing Metadata A snake has an internal skeleton and is a vertebrate. An earthworm lacks an internal skeleton and is an invertebrate. On earth, invertebrates greatly outnumber vertebrates.

Angiosperms are plants that produce flowers.

What do you think of when you hear flowering plants? You probably think of plants like roses, daisies, or even dandelions. But would you think of wheat? Or the grass in your front lawn? Or oak and maple trees in the forest? These and many other plants are angiosperms Opens in modal popup window , the group of plants that produce flowers. Flowers are actually reproductive structures. Like gymnosperms, angiosperms produce pollen. When pollen lands on a flower, sperm cells fertilize the egg cell within the flower, thus producing an embryo that is encased by a seed. Shortly after fertilization, the structure surrounding the seed begins to swell. This structure, or fruit Opens in modal popup window , provides some protection to the growing seed. Its primary function, however, is to promote seed dispersal. Fruit and flowers are structural adaptations that have allowed flowering plants to live in just about every environment on land. Explore a variety of different angiosperm fruits. Fruit Gallery Opens in modal popup window .

Animals are classified in Kingdom Animalia, in Domain Eukarya.

What is it that classifies an organism as an animal? Several characteristics unite this group: All animals are multicellular and eukaryotic. All animals are heterotrophic and digest food inside their bodies. All animals can reproduce sexually. Animals' cells do not have cell walls. Explore the image on-screen to find out how many animals you can discover. If you count two or three, you're on the right track but, in fact, there are more than 15 different animals in the photo.

Flatworms are simple animals with few specialized structures.

What's one of the biggest differences between plants and animals? Plants can make their own food, while animals must eat other organisms-meaning that animals, for the most part, need to graze on or hunt other organisms. Finding food requires the ability to sense the environment and move toward a food source-all of which the flatworm, a relatively simple invertebrate, can do. Some flatworms are invertebrate animals with a distinct head and tail, and a primitive brain. They have bilateral symmetry. Flatworms also have eyespots that are sensitive to light and special structures that detect chemicals in the water. All of these features help flatworms find the tiny organisms they eat. They have a simple digestive system, and obtain the oxygen needed for cellular respiration through simple diffusion. Oxygen gas diffuses directly into the flatworm's body. Throughout the next lessons, pay close attention to a free-living flatworm called a planarian. The genus you will study is Dugesia, which is common in many freshwater environments. Missing Metadata Here are four planarians that have noticeable eyespots.

Some archaeans live in extreme habitats, but many live in places such as soil and seawater.

When scientists first began learning about archaeans, they found them in extreme habitats, such as the extremely salty water of the Great Salt Lake in Utah. Since then, scientists have learned that most archaeans share some DNA sequences, and they have used these sequences to help search for archaeans in other places. It turns out that while archaeans do live in some unusual habitats, many live in more ordinary places, too, such as soil. Missing Metadata Halophiles are archaeans that can survive in extremely salty conditions.

Living things share many basic characteristics and needs.

When you first began your study of biology, you learned that all living organisms share a set of basic characteristics. The characteristics are heredity homeostasis reproduction cellular organization response metabolism growth and development You can review these characteristics on pages 16-17 of your reference book and in the online activity To Be Alive Opens in modal popup window . As you continue to study the different groups of organisms on earth, think about how each type of organism carries out these central life functions. In what ways do groups of organisms differ? In what ways are they the same?

Digestion in many animals is aided by the action of enzymes in the digestive fluids. Mouth: Enzymes in the saliva begin the process of breaking down the starches, glycogen, and sucrose in the food. Stomach: Pepsin in the stomach breaks down proteins and small polypeptides. Pepsin works only in the presence of hydrochloric acid. Small Intestine: Pancreatic fluids and bile salts in the small intestine break down starch, sucrose, amino acids, lipids, and nucleotides.

Whether an animal regurgitates digestive fluids before eating or mixes the fluids internally, those fluids are usually acidic and contain several types of enzymes Opens in modal popup window . The enzymes catalyze the chemical reactions needed to break down large, complex food into specific chemical components. Turn to pages 150-151 of your reference book to learn more about the role of enzymes in digestion.

Fungi can cause significant diseases.

While fungi play many important roles in ecosystems and have significant uses in industry, they also can cause human diseases. Athlete's foot, for example, is a fungal infection of the skin. It causes itching and redness, and sometimes even produces blisters. It's contagious and can be caught by walking barefoot in a moist environment such as a locker room. Another common fungal infection of the skin is ringworm. Despite the name, there's no worm involved: Several different types of fungus may cause this disease, which produces ring-shaped patches on the skin. Some fungal infections can be more serious. Histoplasmosis is a disease of the lungs, caused by a fungus that lives in soil contaminated by bird and bat droppings. People can become infected by inhaling spores in contaminated areas. The infection can be fatal in infants, the elderly, or people with weakened immune systems.

All living things produce waste that must be removed in some manner to maintain homeostasis. All organisms produce and excrete wastes. In general, more complex organisms have more complex systems for waste management.

While humans turn a displeasing face to anything waste related, the fact is that the excretion of waste by living things is an important and critical process. Waste removal keeps the inside of an organism clean and able to have space for continued ingestion of new materials. An internal environment of balance, or homeostasis, cannot be achieved in an organism if waste products build up and are not dealt with in some manner. Organisms produce many types of waste. As a basic rule of thumb, the more complex an organism, the more complex its system for waste management and disposal.

Ferns, flatworms, and humans share some basic characteristics but meet their needs in different ways.

While the three representative organisms you're learning about differ in the ways that each carries out its life functions and meets its needs for energy, they share some basic characteristics: Each organism is dependent on oxygen, breaks down food to provide energy, and is made of eukaryotic cells. In the lessons ahead, you'll learn more specific details about the features unique to each of these organisms.

Kingdom Animalia is classified into several large taxonomic groups, or phyla.

Within each kingdom, species are further classified into groups according to their similarities. The taxonomic group that follows the kingdom level is the phylum. Turn to page 129 of your reference book to see where the category phylum fits in the overall classification scheme. Now turn to the phylogenetic tree on page 138. Note that Kingdom Animalia has a single common ancestor that branches into three lineages. If you follow the animal line, you'll notice the first branch is labeled "sponges," which tells you that the group of animals classified as sponges was the first group to diverge from the earliest common ancestor of animals. The other branches split off later in evolutionary time, as is represented in the tree. Each phylum fits into one of these three groups.

Nephrons are the structural units of the kidney that filter blood. Urine Production The amount of urine produced depends on factors such as hydration, exercise, and diet. Average adult humans produce 1-2 L of urine per day.

Within the renal cortex lie millions of nephrons. Nephrons Opens in modal popup window are minifiltration complexes that actually remove urea and other materials from blood to produce urine. Nephrons collect much more water than is sent as waste. Reabsorption of water occurs in small blood vessels and reenters the main bloodstream. Study the diagram of the nephron on page 155 of your reference book, and then explore the anatomy of a nephron.

Carbon dioxide, the waste product of cellular respiration, travels from the circulatory system and out through the respiratory system. Text Version Heart, Lungs, and Carbon Dioxide Positioned in the center of the space is a diagram of the heart, lung capillaries, and body capillaries. Positioned above the heart are the lung capillaries. Positioned below the heart are the body capillaries. The capillaries are represented by net-like structures. The right side of the heart is light. A light path-like structure, labeled artery, connects the right side of the heart to the right side of the lung capillaries. A second light path-like structure connects the right side of the heart to the right side of the body capillaries. The left side of the heart is dark. A dark path-like structure, labeled vein, connects the left side of the heart to the left side of the lung capillaries. A second dark path-like structure connects the left side of the heart to the left side of the body capillaries. The part of the lung and body capillaries on the right are light and correspond with the light part of the heart. The capillaries change gradually from light on the right to dark on the left. A system of arrows highlights in sequence. The sequence shows the flow of carbon dioxide through the body. The flow is as follows: Arrows show that carbon dioxide flows from the right side of the lung capillaries down to the right side of the heart. Arrows show that carbon dioxide flows through the heart and then up, around, and down through the artery to the body capillaries. Carbon dioxide flows through the body capillaries from right to left to the vein that carries the carbon dioxide up to the left side of the heart. From the left side of the heart, arrows show that carbon dioxide flows up and around to the left side of the lung capillaries. Carbon dioxide moves from the left side of the lung capillaries to the right side where it becomes light. From there the cycle begins again, with carbon dioxide flowing to the right side of the heart.

You already know from the lesson on waste that carbon dioxide is removed from the body. It is removed almost along the same path as oxygen comes in. However, there is one major difference—and it is in the circulatory system. In the respiratory system, the same exact tubes, including the alveoli, are used to bring in oxygen and remove carbon dioxide. Yet, in the circulatory system, a different set of vessels carry oxygenated and deoxygenated blood. Arteries are the vessels that carry the oxygen-filled blood to the cells. Veins Opens in modal popup window are a complementary set of vessels that carry carbon dioxide back to the heart and lungs. Just like oxygen, carbon dioxide diffuses out of the cells and into the capillaries. Once carbon dioxide reaches the capillaries in the lungs, it diffuses into the alveoli. In this stage of respiration, carbon dioxide travels through the veins from the body capillaries to the lung capillaries. Remember that the circulatory system is a closed loop, and blood is continuously in motion.

After being produced in the kidneys, urine travels to the urinary bladder, which stores urine until it is excreted from the urethra. Urinary Bladder Capacity The average urinary bladder can hold 50-53 cL (17-18 oz) of urine, but the urge to urinate is triggered at around 21-24 cL (7-8 oz).

You can relate to that child in the restaurant bathroom, because even though you have some control over your waste elimination, there is a limit, and sometimes that limit is pushed pretty far. The urinary bladder is the next stop on this tour of urine production. Leaving through the renal pelvis, urine from both kidneys passes through the ureter Opens in modal popup window and enters into the bladder, which is a muscular, elastic organ that stores urine. As more urine enters the bladder, more pressure is placed on its walls, causing them to stretch. When stretched far enough, they activate certain nerves that send messages to your brain that it is time to release the urine. Two sphincter muscles keep the urinary bladder shut: The first is an involuntary muscle, while the second you control. These muscles provide double protection to prevent incontinence, or lack of control of waste excretion. A tube called the urethra Opens in modal popup window extends from the urinary bladder out of the body, and is the actual site of excretion. The scientific term for urination is micturate.

3.10 Getting Energy All living things must take in energy consistently to survive. Living Things need energy. autotrophs make their own food and heterotrophs consume food

You may think your life is quite different from the life of a plant, insect, or other animal. You do far more than just survive—you read and write, go to school or work, watch movies, play sports, and much more. But at the end of the day, you are just like all other forms of life in that you need to take in energy to survive.

The liver filters waste from the blood and produces urea. The liver filters nitrogenous waste out of the blood, converts it to urea, and sends it to the kidneys. The liver also filters out and stores other toxins as well.

You're waiting in line to use the restroom at a restaurant. Suddenly, a desperate parent bursts in, pulling by the hand a very wiggly child. Responding to pleading eyes, you graciously step back, allowing the distressed pair to take the next available stall. However, long before the near accident, the child's production of urea, the major component of urine, started in the liver Opens in modal popup window . After leaving the small intestine, blood, full of newly digested food materials, goes to the liver for further processing and filtration. One of the main filtering jobs of the liver is to remove nitrogenous waste that is a result of protein digestion. This waste is converted into a substance called urea-a waste product. Another waste-related function of the liver is to remove toxins from blood. Toxins, such as pollutants from the environment, are filtered and stored in the liver.

Single-cell organisms obtain oxygen by diffusion. Human Cells vs. Bacterial Cells Your body contains 10 times as many bacterial cells as it does actual human cells

Your body contains more bacterial cells than it does human cells. These multipurpose, single-cell organisms inhabit you. Thankfully, they are so tiny that you don't have to watch them reproduce on your skin, munch away at your hair oils, or squirm in your latest pimple or in the food stuck in your teeth. But, they are there and on nearly all other places on earth. Do bacteria take in oxygen? Yes, most of them do, and they do it for the same reason you do—to produce ATP via cellular respiration. How does a single cell take in oxygen? Well, the only possible way is through diffusion. Since bacteria have no tissues or organs, the only way is through the cell membrane. Like bacteria, single-cell organisms such as the amoebas at right also take in oxygen by diffusion across their cell membranes. Single-cell organisms, such as amoebas, obtain oxygen by diffusion.

angiosperm

a flowering plant

fruit FRUIT GALLERY: An apple develops from the swollen ovary of a flower. Inside the apple are numerous seeds. Apple seeds can pass through the digestive tracts of many animals without doing serious damage. By providing a nutritious, sweet snack to animals, the apple tree cleverly disperses its seeds to new locations in animal waste. The flower of a peanut plant grows just aboveground. After fertilization, the ovary of the flower grows underground as a pod, becoming the fruit. Peanuts have been cultivated throughout the world for thousands of years, but the plant is thought to have originated in South America. Peanut seeds are nutritious and are used as a food source all over the world. This weed is commonly known as a cobbler's peg (Bidens pilosa). The seeds of this flowering plant are shown in the picture. The spines on the ends of the seeds catch in fur and clothing. Instead of dispersing its seeds inside a sweet fruit like an apple does, the cobbler's peg disperses its seeds by hitchhiking on unsuspecting animals. This dandelion is also a fruit. It is not succulent and sweet, but it does contain a seed. Dandelion seeds are dispersed widely by the wind. The fairylike fruit can travel very long distances by wind power alone. The double samara of a maple tree is a fruit as well. It contains two seeds. Once the fruit has dried out, it breaks away from the stem that attaches it to the tree. The samara moves through the air like a helicopter, with wind dispersing the seeds to new locations.

a mature ovary that contains seeds

vesicle

a small, membrane-enclosed structure inside a cell involved in storing and transporting substances

seed

an ovule that has been fertilized and now contains an embryo surrounded by a seed coat

The Process of Digestion

food enters digestive system digestive system breaks down food into chemical components components move into body cells 1. In the mouth, the teeth break food into small pieces, and enzymes in the saliva break it down even further. 2. Muscles in the esophagus push food down into the stomach. 3. The stomach secretes hydrochloric acid and enzymes that break down the food, particularly the proteins in the food. The acidic environment kills many germs in the food. 4. Food moves into the small intestine, which absorbs nutrients and transfers them to the bloodstream. 5. The liver secretes bile salts into the small intestine to help break apart fats in the food. 6. The gallbladder stores bile from the liver and secretes it into the small intestine to help break down fats. 7. The pancreas secretes more enzymes into the small intestine to break down the food, and it also adds an alkaline solution that helps neutralize the stomach acids. 8. The leftover products enter the large intestine, which removes most of the water. Bacteria in the large intestine aid in the production and absorption of vitamins into the body. 9. The leftover products of digestion, now called feces, move into the rectum, which stores waste until it can be expelled.

Vascular Tissues

in plants, specialized internal tissue that conducts water and minerals, as well as sugars, such as glucose

photosynthesis

the process by which plants and certain other organisms use the energy of sunlight to convert carbon dioxide and water into sugar and oxygen