ENVS2202 Lesson 2A: Ecosystems

Elements or water may be held for various lengths of time by different components of a biogeochemical cycle.

Components that hold elements or water for a relatively short period of time are called exchange pools. For example, the atmosphere is an exchange pool for water. It holds water for several days at the longest. This is a very short time compared with the thousands of years the deep ocean can hold water. The ocean is an example of a reservoir for water. Reservoirs are components of a geochemical cycle that hold elements or water for a relatively long period of time.

Some chemosynthetic bacteria live around deep-ocean vents known as "black smokers."

Compounds such as hydrogen sulfide, which flow out of the vents from Earth's interior, are used by the bacteria for energy to make food. Consumers that depend on these bacteria to produce food for them include giant tubeworms,

CONSUMERS

Consumers are organisms that depend on the producers (phototrophs or chemotrophs) organisms for food. They take in organic molecules by essentially "eating" other living things. They include all animals and fungi. (Fungi don't really "eat"; they absorb nutrients from other organisms.) They also include many bacteria and even a few plants, such as the pitcher plant in Figure below. Consumers are also called heterotrophs. Heterotrophs are classified by what they eat:

water cycle

Earth's water is constantly in motion. Although the water on Earth is billions of years old, individual water molecules are always moving through the water cycle. The water cycle describes the continuous movement of water molecules on, above, and below Earth's surface. It is shown in Figure 4.1. Like other biogeochemical cycles, there is no beginning or end to the water cycle. It just keeps repeating. During the cycle, water occurs in its three different states: gas (water vapor), liquid (water), and solid (ice). Processes involved in changes of state in the water cycle include evaporation, sublimation, and transpiration. The water cycle is demonstrated at http://www.youtube.com/watch?v=iohKd5FWZOE&feature=related (4:00).

ecological pyramid

Ecological Pyramid. This pyramid shows how energy and biomass decrease from lower to higher trophic levels. Assume that producers in this pyramid have 1,000,000 kilocalories of energy. How much energy is available to primary consumers?

population

Ecologists also study organisms and their environments at the population level. A population consists of organisms of the same species that live in the same area and interact with one another. You will read more about populations in the Populations chapter. Important ecological issues at the population level include: • rapid growth of the human population, which has led to overpopulation and environmental damage; • rapid decline in populations of many nonhuman species, which has led to the extinction of numerous species.

levels of organization

Ecologists study organisms and their environments at different levels. The most inclusive level is the biosphere. The biosphere consists of all the organisms on planet Earth and the areas where they live. It occurs in a very thin layer of the planet, extending from about 11,000 meters below sea level to 15,000 meters above sea level. An image of the biosphere is shown in Figure 6.1. Different colors on the map indicate the numbers of food-producing organisms in different parts of the biosphere. Ecological issues that might be investigated at the biosphere level include ocean pollution, air pollution, and global climate change.

Chemoautotrophs

In some places where life is found on Earth, there is not enough light to provide energy for photosynthesis. In these places, producers called chemoautotrophs use the energy stored in chemical compounds to make organic molecules by chemosynthesis. include bacteria called nitrifying bacteria, which you will read more about in Lesson 3. Nitrifying bacteria live underground in soil. They oxidize nitrogen-containing compounds and change them to a form that plants can use. Chemoautotrophs also include archaea.

nitrogen cycle

The atmosphere is the largest reservoir of nitrogen on Earth. It consists of 78 percent nitrogen gas (N2). The nitrogen cycle moves nitrogen through abiotic and biotic components of ecosystems. Figure 4.3 shows how nitrogen cycles through a terrestrial ecosystem. Nitrogen passes from the atmosphere into soil. Then it moves through several different organisms before returning to the atmosphere to complete the cycle. In aquatic ecosystems, nitrogen passes through a similar cycle. The nitrogen cycle ( 6d) is discussed at http://www.youtube.com/watch?v=pdY4I-EaqJA&feature=fvw (5:08).

second law of thermodynamics

is also important to environmental science and states that disorganization, or entropy, increases in natural systems through any spontaneous process. This means that as energy is used it is degraded to lower forms of energy.

A ecological footprint

is an evaluation of how much effect a person has on the environment. It is defined as the measure of your demand on natural resources and the Earth's natural systems.

Lactic acid fermentation

is carried out by the bacteria in yogurt. It is also used by your own muscle cells when you work them hard and fast. Did you ever run a race and notice that your muscles feel tired and sore afterward? This is because your muscle cells used lactic acid fermentation for energy. This causes lactic acid to build up in the muscles. It is the buildup of lactic acid that makes the muscles feel tired and sore.

producers

organisms that produce food for themselves and other organisms. They use energy and simple inorganic molecules to make organic compounds. The stability of producers is vital to ecosystems because all organisms need organic molecules. Producers are also called autotrophs. There are two basic types of autotrophs: photoautotrophs and chemoautotrophs.

archaea

re a domain of microorganisms that resemble bacteria. Most archaea live in extreme environments, such as around hydrothermal vents in the deep ocean. Hot water containing hydrogen sulfide and other toxic substances escapes from the ocean floor at these vents, creating a hostile environ- ment for most organisms. Near the vents, archaea cover the sea floor or live in or on the bodies of other organisms, such as tube worms. In these ecosystems, archaea use the toxic chemicals released from the vents to produce organic compounds. The organic compounds can then be used by other organisms, including tube worms. Archaea are able to sustain thriving communities, like the one shown in Figure 6.4, even in these hostile environments.

Both cyanobacteria and algae make up phytoplankton. Phytoplankton

refers to all the tiny photoautotrophs found on or near the surface of a body of water. Phytoplankton usually is the primary producer in aquatic ecosystems.

the laws of ecology

serve to remind us of our place within our natural systems, and that humans are, ultimately, an animal too that must adhere to the natural rules that govern the planet. They are rules about how all life on Earth functions, and what factors to consider in our daily lives, social development, land use, and business practices.

The first law of thermodynamics, or, the conservation of energy principle,

states that energy may change from one form to another, but the total amount of energy will remain constant. That is to say that energy is not destroyed or created; it just changes form. For example, when wood is burned, the energy that was stored in the wood is not lost. It is given off as heat, smoke, and ash. The final amount of energy is the same just in new forms

thermodynamics

the study of energy and the laws of thermodynamics, as you already learned about them, can be applied to energy flow in ecosystems.

Ecology

the study of how living things interact with each other and with their environment. It is a major branch of biology, but has areas of overlap with geography, geology, climatology, environmental science, and other sciences. This chapter introduces fundamental concepts in ecology related to organisms and the environment.

Cellular respiration that proceeds without oxygen is called anaerobic respiration

this was probably the first kind of respiration present in organisms before oxygen levels increased in the atmosphere. About 2 or 3 billion years ago, oxygen was gradually added to the atmosphere by early photosynthetic bacteria. After that, living things could use oxygen for respiration. Cellular respiration that proceeds in the presence of oxygen is called aerobic respiration.

biotic factors

are the living aspects of the environment. They consist of other organisms, including members of the same and different species.

abiotic factors

are the nonliving aspects of the environment. They include factors such as sunlight, soil, temperature, and water.

fermentation

An important way of making energy without oxygen is called fermentation. Many bacteria and yeasts carry out fermentation. People use these organisms to make yogurt, bread, wine, and biofuels. Human muscle cells also use fermentation. This occurs when muscle cells cannot get oxygen fast enough to meet their energy needs through aerobic respiration. There are two types of fermentation: lactic acid fermentation and alcoholic fermentation.

community

Another level at which ecologists study organisms and their environments is the community level. A community consists of populations of different species that live in the same area and interact with one another. For example,populations of coyotes and rabbits might interact in a grassland community. Coyotes hunt down and eat rabbits for food, so the two species have a predator-prey relationship. Ecological issues at the community level include how changes in the size of one population affect other populations.

The Importance of Energy

As you already learned, energy is defined as the ability move things, do work, or transfer heat, and comes in various forms, including light, heat, and electricity. There is Low-quality energy that comes in dispersed forms and High- quality energy comes in condensed forms.

After being used by plants and animals, nitrogen is released back into the environment. When decomposers break down organic remains and wastes, they release nitrogen in the form of ammonium ions (NH4−). This is called ammonification. It occurs in both terrestrial and aquatic ecosystems. In terrestrial ecosystems, some nitrogen- fixing bacteria in soil and root nodules also convert nitrogen gas directly into ammonium ions.

Although some plants can absorb nitrogen in the form of ammonium ions, others cannot. In fact, ammonium ions may be toxic to some plants and other organisms. Certain soil bacteria, called nitrifying bacteria, convert ammonium ions to nitrites (NO2−). Other nitrifying bacteria convert the nitrites to nitrates, which plants can absorb. The process of converting ammonium ions to nitrites or nitrates is called nitrification.

Competitive Exclusion Principle

A given habitat may contain many different species, but each species must have a different niche. Two different species cannot occupy the same niche in the same place for very long. This is known as the competitive exclusion principle. If two species were to occupy the same niche, what do you think would happen? They would compete with one another for the same food and other resources in the environment. Eventually, one species would be likely to outcompete and replace the other.

methane

A much smaller amount of carbon in the atmosphere is present as methane gas (CH4). Methane is released into the atmosphere when dead organisms and other organic matter decay in the absence of oxygen. It is produced by landfills, the mining of fossil fuels, and some types of agriculture.

the ecosystem

An ecosystem is a unit of nature and the focus of study in ecology. It consists of all the biotic and abiotic factors in an area and their interactions. Ecosystems can vary in size. A lake could be considered an ecosystem. So could a dead log on a forest floor. Both the lake and log contain a variety of species that interact with each other and with abiotic factors.

why these laws are important to ENVS?

1. First, and very important: we live in a closed system, the Earth's ecosphere. Nearly all of the organisms on Earth obtain their energy from the sun, and the sun composes the primary level of most ecosystem food chains, save a few deep-water thermal vents and some geyser bacteria. Since energy is neither created nor destroyed, as stated by the first law of thermodynamics, we can conclude that other than the sun's energy, the energy present is what we have to work with, including the food you live on 2. Second, when humans use non-renewable resources (such as oil) they are converting them into less-useful energy, as stated by the second law of thermodynamics. When those energy sources are depleted, they are gone. Use of these energy sources often also releases different elements back into the environment. For example, the combustion of oil releases carbon back into the air, and this offsets the carbon cycle ( which you learn about ). This helps contribute to climate change. there are inputs and outputs to all energy types, and also benefits and costs to each kind. and each is controlled and limited within the laws of both ecology and thermodynamics.

biochemical cycles

A biogeochemical cycle is a closed loop through which a chemical element or water moves through ecosystems. In the term biogeochemical, bio- refers to biotic components and geo- to geological and other abiotic components. Chemicals cycle through both biotic and abiotic components of ecosystems. For example, an element might move from the atmosphere to ocean water, from ocean water to ocean organisms, and then back to the atmosphere to repeat the cycle.

food chains

A food chain represents a single pathway through which energy and matter flow through an ecosystem. An example is shown in Figure 6.15. Food chains are generally simpler than what really happens in nature. Most organisms consume—and are consumed by—more than one species. A musical summary of food chains can be heard at http://www.youtube.com/watch?v=TE6wqG4nb3M (2:46).

food webs

A food web represents multiple pathways through which energy and matter flow through an ecosystem. It includes many intersecting food chains. It demonstrates that most organisms eat, and are eaten, by more than one species. An example is shown in Figure 6.16

carbon in the biosphere

Bicarbonate ions near the surface of the ocean may be taken up by photosynthetic algae and bacteria that live near the surface. These and other autotrophic organisms use bicarbonate ions or other forms of carbon to synthesize organic compounds. Carbon is essential for life because it is the main ingredient of every type of organic compound. Organic compounds make up the cells and tissues of all organisms and keep organisms alive and functioning. Carbon enters all ecosystems, both terrestrial and aquatic, through autotrophs such as plants or algae. Autotrophs use carbon dioxide from the air, or bicarbonate ions from the water, to make organic compounds such as glucose. Heterotrophs consume the organic molecules and pass the carbon through food chains and webs. How does carbon cycle back to the atmosphere or ocean? All organisms release carbon dioxide as a byproduct of cellular respiration. Recall from the Cellular Respiration chapter that cellular respiration is the process by which cells oxidize glucose and produce carbon dioxide, water, and energy. Decomposers also release carbon dioxide when they break down dead organisms and other organic waste. In a balanced ecosystem, the amount of carbon used in photosynthesis and passed through the ecosystem is about the same as the amount given off in respiration and decomposition. This cycling of carbon between the atmosphere and organisms forms an organic pathway in the carbon cycle. Carbon can cycle quickly through this organic pathway, especially in aquatic ecosystems. In fact, during a given period of time, much more carbon is recycled through the organic pathway than through the geological pathway you will read about next.

subduction volcanism

Carbon-containing rocks and sediments on the ocean floor gradually move toward the edges of the ocean due to a process called seafloor spreading. The rocks eventually reach cracks in the crust, where they are pulled down into the mantle. This process, called subduction, occurs at subduction zones. In the mantle, the rocks melt and their carbon is stored. When volcanoes erupt, they return some of the stored carbon in the mantle to the atmosphere in the form of carbon dioxide, a process known as volcanism. This brings the geological pathway of the carbon cycle full circle.

cellular respiration

Cellular respiration occurs in the cells of all living things. This process occurs not only in plants, but also in humans and animals. So, unlike photosynthesis, respiration can occur during both the day and night. During respiration, carbon is removed from organic materials and expelled into the atmosphere as carbon dioxide.

chapter 6 summary

Ecology is the study of how living things interact with each other and with their environment. The environment includes abiotic (nonliving) and biotic (living) factors. An ecosystem consists of all the biotic and abiotic factors in an area and their interactions. A niche refers to the role of a species in its ecosystem. A habitat is the physical environment in which a species lives and to which it is adapted. Two different species cannot occupy the same niche in the same place for very long. Ecosystems require constant inputs of energy from sunlight or chemicals. Producers use energy and inorganic molecules to make food. Consumers take in food by eating producers or other living things. Decomposers break down dead organisms and other organic wastes and release inorganic molecules back to the environment. Food chains and food webs are diagrams that represent feeding relationships. They model how energy and matter move through ecosystems. The different feeding positions in a food chain or web are called trophic levels. Generally, there are no more than four trophic levels because energy and biomass decrease from lower to higher levels. Living things need energy to carry out all life processes. They get energy from food. Autotrophs make their own food. Heterotrophs get food by eating other living things. Most autotrophs make food using photosynthesis. This process occurs in two stages: the light reactions and the Calvin cycle. Some bacterial autotrophs make food using chemosynthesis. This process uses chemical energy instead of light energy to produce food. Many autotrophs make food through the process of photosynthesis, in which light energy from the sun is changed to chemical energy that is stored in glucose. All organisms use cellular respiration to break down glucose, release energy. Living things must have chemical energy from food to power life processes. Most of the chemical energy in food comes ultimately from the energy in sunlight. The last two stages of aerobic respiration require oxygen. However, not all organisms live in places where there is a plentiful supply of oxygen so they use anaerobic respiration instead, which does not require oxygen. Competition among species is an important factor in co-evolution. The Four Laws of Ecology are important reference points about ecosystems and natural communities function, and are the basis for the balanced and sustained ways that natural systems are supported.

Flow of Energy: Producers and Consumers

Energy enters ecosystems in the form of sunlight or chemical compounds. Some organisms use this energy to make food. Other organisms get energy by eating the food.

food chains & food webs

Food chains and food webs are diagrams that represent feeding relationships. They show who eats whom. In this way, they model how energy and matter move through ecosystems.

Today, most living things use oxygen to make energy from glucose (aerobic respiration).

However, many living things can still also make energy for life without oxygen. This is true of some plants and fungi and also of many bacteria. These organisms use aerobic respiration when oxygen is present, but when oxygen is in short supply, they use anaerobic respiration instead. Certain bacteria can only use anaerobic respiration. In fact, they may not be able to survive at all in the presence of oxygen.

habitat destruction

Human destruction of habitats is the major factor causing other species to decrease and become endangered or go extinct. Small habitats can support only small populations of organisms. Small populations are more susceptible to being wiped out by catastrophic events from which a large population could bounce back. Habitat destruction caused the extinction of the dusky seaside sparrow shown in Figure below.

carbon in the atmosphere

In the atmosphere, carbon exists primarily as carbon dioxide (CO2). Carbon dioxide enters the atmosphere from several different sources, including those listed below. Most of the sources are also represented in Figure 2, and some are described in detail later in the lesson. • Living organisms release carbon dioxide as a byproduct of cellular respiration. • Carbon dioxide is given off when dead organisms and other organic materials decompose. • Burning organic material, such as fossil fuels, releases carbon dioxide. • When volcanoes erupt, they give off carbon dioxide that is stored in the mantle. • Carbon dioxide is released when limestone is heated during the production of cement. • Ocean water releases dissolved carbon dioxide into the atmosphere when water temperature rises.

Still other bacteria, called denitrifying bacteria, convert some of the nitrates in soil back into nitrogen gas in a process called denitrification. The process is the opposite of nitrogen fixation. Denitrification returns nitrogen gas back to the atmosphere, where it can continue the nitrogen cycle.

In the ocean, another reaction occurs to cycle nitrogen back to nitrogen gas in the atmosphere. The reaction, called the anammox reaction, is enabled by certain bacteria in the water. In the reaction, ammonium and nitrite ions combine to form water and nitrogen gas. This is shown by the equation: NH4+ + NO2− → N2 + 2H2O. The anammox reaction may contribute up to half of the nitrogen gas released into the atmosphere by the ocean. The reaction may also significantly limit production in ocean ecosystems by removing nitrogen compounds that are needed by aquatic producers and other organisms.

The process of converting nitrogen gas to nitrate ions that plants can absorb is called nitrogen fixation.

It is carried out mainly by nitrogen-fixing bacteria, which secrete enzymes needed for the process. Some nitrogen-fixing bacteria live in soil. Others live in the root nodules of legumes such as peas and beans. In aquatic ecosystems, some cyanobacteria are nitrogen fixing. They convert nitrogen gas to nitrate ions that algae and other aquatic producers can use. Nitrogen gas in the atmosphere can be converted to nitrates by several other means. One way is by the energy in lightning. Nitrogen is also converted to nitrates as a result of certain human activities. These include the production of fertilizers and explosives and the burning of fossil fuels. These human activities also create the gas nitrous oxide (N2O). The concentration of this gas in the atmosphere has tripled over the past hundred years as a result. Nitrous oxide is a greenhouse gas that contributes to global warming and other environmental problems.

1st Trophic Level: Producer-- Makes its own food --Plants make food 2nd Trophic Level: Primary Consumer--Consumes producers--Mice eat plant seeds 3rd Trophic Level: Secondary Consumer--Consumes primary consumers--snakes eat mice 4th trophic level:Tertiary Consumer--Consumes secondary consumers--hawks eat snakes

Many consumers feed at more than one trophic level. Humans, for example, are primary consumers when they eat plants such as vegetables. They are secondary consumers when they eat cows. They are tertiary consumers when they eat salmon.

ch 4 summary

Matter cycles are important means of putting nutrients back into ecosystems. Biogeochemical cycles are closed loops through which chemical elements or water move through ecosystems. Examples of biogeochemical cycles include the water cycle, carbon cycle, and nitrogen cycle. The water cycle recycles water through ecosystems. Processes by which water changes state in the water cycle include evaporation, sublimation, transpiration, and condensation. The organic pathway of the carbon cycle moves carbon from the atmosphere, through producers and other organisms in ecosystems, and back to the atmosphere. The geological pathway moves carbon from the atmosphere, through the ocean to rocks and the mantle, and back to the atmosphere. The nitrogen cycle moves nitrogen gas from the atmosphere into soil or water, where nitrogen-fixing bacteria convert it to a form that producers can use. Nitrifying bacteria help nitrogen cycle through ecosystems. Denitrifying bacteria return nitrogen gas back to the atmosphere. The anammox reaction returns nitrogen back to the atmosphere from ocean water.

carbon in ocean water

Most carbon enters the ocean when carbon dioxide in the atmosphere dissolves in ocean water. When carbon dioxide dissolves in water (H2O), it forms an acid called carbonic acid (H2CO3). The reaction is given by the equation: CO2 + H2O ↔ H2CO3. The double-headed arrow indicates that the reaction can occur in either direction, depending on the conditions and the amount of carbon dioxide present. For example, the reaction occurs more readily in the left-to-right direction in cold water. As a result, near the poles, where ocean water is cooler, more carbon dioxide is dissolved and there is more carbonic acid in the water. Although carbonic acid is a weak acid, it is an important regulator of the acid-base (pH) balance of ocean water. Carbonic acid, in turn, readily separates into hydrogen ions (H+) and bicarbonate ions (HCO3−). This occurs in the following reaction: H2CO3 ↔ H+ + HCO3−. Due to these two reactions, most dissolved carbon dioxide in the ocean is in the form of bicarbonate ions. Another source of bicarbonate ions in ocean water is runoff. Flowing water erodes rocks containing carbon compounds such as calcium carbonate. This forms bicarbonate ions, which the runoff carries to streams, rivers, and eventually the ocean. Many of the bicarbonate ions in ocean water are moved by ocean currents into the deep ocean. Carbon can be held in this deep ocean reservoir as bicarbonate ions for thousands of years or more.

Photosynthesis Plants and other autotrophs make food out of "thin air"—at least, they use carbon dioxide from the air to make food.

Most food is made in the process of photosynthesis. This process provides more than 99% of the energy used by living things on Earth. Photosynthesis also supplies Earth's atmosphere with oxygen. Photosynthesis is often considered to be the single most important life process on Earth. It changes light energy into chemical energy and also releases oxygen. Without photosynthesis, there would be no oxygen in the atmosphere.

Herbivores consume producers such as plants or algae. They are a necessary link between producers and other consumers. Examples include deer, rabbits, and mice. • Carnivores consume animals. Examples include lions, polar bears, hawks, frogs, salmon, and spiders. Carnivores that are unable to digest plants and must eat only animals are called obligate carnivores. Other carnivores can digest plants but do not commonly eat them.

Omnivores consume both plants and animals. They include humans, pigs, brown bears, gulls, crows, and some species of fish.

niche

One of the most important concepts associated with the ecosystem is the niche. A niche refers to the role of a species in its ecosystem. It includes all the ways that the species interacts with the biotic and abiotic factors of the environment. Two important aspects of a species' niche are the food it eats and how the food is obtained. Look at Figure 6.3. It shows pictures of birds that occupy different niches. Each species eats a different type of food and obtains the food in a different way.

organisms & the environment

Organisms are individual living things. Despite their tremendous diversity, all organisms have the same basic needs: energy and matter. These must be obtained from the environment. Therefore, organisms are not closed systems. They depend on and are influenced by their environment. The environment includes two types of factors: abiotic and biotic.

Chemoautotrophs use energy from chemical compounds to make food by chemosynthesis. They include some bacteria and also archaea. Archaea are microorganisms that resemble bacteria.

Photoautotrophs use energy from sunlight to make food by photosynthesis. They include plants, algae, and certain bacteria

recycling matter

Unlike energy, elements are not lost and replaced as they pass through ecosystems. Instead, they are recycled repeatedly. All chemical elements that are needed by living things are recycled in ecosystems, including carbon, nitrogen, hydrogen, oxygen, phosphorus, and sulfur. Water is also recycled.

During photosynthesis, raw materials are used to manufacture sugar (glucose). Photosynthesis occurs in the presence of chlorophyll, a green plant pigment that helps the plant utilize the energy from sunlight to drive the process. Although the overall process involves a series of reactions, the net reaction can be represented by the following:

Photosynthetic autotrophs (such as plants) capture light energy from the sun and absorb carbon dioxide and water from their environment. Using the light energy, they combine the reactants to produce glucose and oxygen, which is a waste product. They store the glucose, usually as starch, and they release the oxygen into the atmosphere. The sugar provides a source of energy for other plant processes and is also used for synthesizing materials necessary for plant growth and maintenance. The net effect with regard to carbon is that it is removed from the atmosphere and incorporated into the plant as organic materials. Photosynthesis occurs in two stages: the Light Reactions and the Calvin Cycle, which both take place in the chloroplast of plants and other chlorophyll containing organisms.

Absorption of Nitrogen

Plants and other producers use nitrogen to synthesize nitrogen-containing organic compounds. These include chlorophyll, proteins, and nucleic acids. Other organisms that consume producers make use of the nitrogen in these organic compounds. Plants absorb substances such as nitrogen from the soil through their root hairs. However, they cannot absorb nitrogen gas directly. They can absorb nitrogen only in the form of nitrogen-containing ions, such as nitrate ions (NO3−).

condensation and precipitation

Rising air currents carry water vapor from all these sources into the atmosphere. As the water vapor rises higher into the atmosphere or is carried toward the poles by winds, the air becomes cooler. Cooler air cannot hold as much water vapor, so the water vapor condenses into tiny water droplets around particles in the air. The tiny water droplets form clouds. Air currents cause the tiny water droplets in clouds to collide and merge into larger droplets. When water droplets in clouds become large enough to fall, they become precipitation. Most precipitation falls back into the ocean. Precipitation that falls at high altitudes or near the poles can accumulate as ice caps and glaciers. These masses of ice can store frozen water for hundreds of years or longer.

carbon cycle

Runoff, streams, and rivers can gradually dissolve carbon in rocks and carry it to the ocean. The ocean is a major reservoir for stored carbon. It is just one of four major reservoirs. The other three are the atmosphere, the biosphere, and organic sediments such as fossil fuels. Fossil fuels, including petroleum and coal, form from the remains of dead organisms. All of these reservoirs of carbon are interconnected by pathways of exchange in the carbon cycle The carbon cycle ( 6d) is discussed in the following video: http://www.youtube.com/watch?v=0Vwa6qtEih8 (1:56).

The Chloroplast: Theater for Photosynthesis

The "theater" where both stages of photosynthesis take place is the chloroplast. Chloroplasts are organelles that are found in the cells of plants and algae. (Photosynthetic bacteria do not have chloroplasts, but they contain structures similar to chloroplasts and produce food in the same way.) Look at the Figure 6.12. The figure is a high power microscopic photo of the upper part of a Winter Jasmine leaf. If you could look at a single leaf of this plant under a microscope, you would see small green ovals, like those shown. These small green ovals are chloroplasts.

trophic levels

The different feeding positions in a food chain or web are called trophic levels. The first trophic level consists of producers, the second of primary consumers, the third of secondary consumers, and so on. There usually are no more than four or five trophic levels in a food chain or web. Humans may fall into second, third, and fourth trophic levels of food chains or webs. They eat producers such as grain, primary consumers such as cows, and tertiary consumers such as salmon. Energy is passed up the food chain from one trophic level to the next. However, only about 10 percent of the total energy stored in organisms at one trophic level is actually transferred to organisms at the next trophic level. The rest of the energy is used for metabolic processes or lost to the environment as heat. As a result, less energy is available to organisms at each successive trophic level. This explains why there are rarely more than four or five trophic levels. The amount of energy at different trophic levels can be represented by an energy pyramid like the one in Figure 6.17.

trophic levels

The feeding positions in a food chain or web are called trophic levels. The different trophic levels are defined in Table 6.1. Examples are also given in the table. All food chains and webs have at least two or three trophic levels. Generally, there are a maximum of four trophic levels.

Photosynthesis Stage I: The Light Reactions

The first stage of photosynthesis is called the light reactions. During this stage, light is absorbed and transformed to chemical energy. By the end of stage 1, energy from sunlight has been changed to chemical energy, and the first stage of photosynthesis is now complete.

Making and Using Food: Photosynthesis and Cellular Respiration

The flow of energy through living organisms begins with photosynthesis. This process stores energy from sunlight in the chemical bonds of glucose. By breaking the chemical bonds in glucose, cells release the stored energy and make the ATP they need. The process in which glucose is broken down for energy is called cellular respiration. Photosynthesis and cellular respiration are like two sides of the same coin. The products of one process are the reactants of the other. Together, the two processes store and release energy in living organisms. The two processes also work together to recycle oxygen in Earth's atmosphere.

carbon in rocks & sediments

The geological pathway of the carbon cycle takes much longer than the organic pathway described above. In fact, it usually takes millions of years for carbon to cycle through the geological pathway. It involves processes such as rock formation, subduction, and volcanism. As stated previously, most carbon in ocean water is in the form of bicarbonate ions. Bicarbonate ions may bind with other ions, such as calcium ions (Ca+) or magnesium ions (Mg+), and form insoluble compounds. Because the compounds are insoluble, they precipitate out of water and gradually form sedimentary rock, such as limestone (calcium carbonate, CaCO3) or dolomite [calcium magnesium carbonate CaMg(CO3)2. Dead organisms also settle to the bottom of the ocean. Many of them have shells containing calcium carbonate. Over millions of years, the pressure of additional layers of sediments gradually changes their calcium carbonate and other remaining organic compounds to carbon-containing sedimentary rock. During some periods in Earth's history, very rich organic sediments were deposited. These deposits formed pockets of hydrocarbons. Hydrocarbons are organic compounds that contain only carbon and hydrogen. The hydrocarbons found in sediments are fossil fuels such as natural gas. The hydrocarbon methane is the chief component of natural gas.

habitat

The habitat is the physical environment in which a species lives and to which it is adapted. A habitat's features are determined mainly by abiotic factors such as temperature and rainfall. These factors also influence the traits of the organisms that live there. Consider a habitat with very low temperatures. Mammals that live in the habitat must have insulation to help them stay warm. Otherwise, their body temperature will drop to a level that is too low for survival. Species that live in these habitats have evolved fur, blubber, and other traits that provide insulation in order for them to survive in the cold.

Photosynthesis Stage II: The Calvin Cycle

The reactions of this stage can occur without light, so they are sometimes called light-independent or dark reactions. This stage of photosynthesis is also known as the Calvin cycle because its reactions were discovered by a scientist named Melvin Calvin. He won a Nobel Prize in 1961 for this important discovery. In the Calvin cycle, chemical energy from the light reactions is used to make glucose. The Calvin cycle takes over where the light reactions end. It uses stored chemical energy (from the light reactions) and carbon dioxide from the air to produce glucose, the molecule that virtually all organisms use for food.

Cellular Respiration High power microscopic photo of the upper part of a Winter Jasmine leaf. Viewed under a microscope many green chloroplasts are visible. You have just read how photosynthesis stores energy in glucose. How do living things make use of this stored energy? The answer is cellular respiration. This process releases the energy in glucose to make ATP, the molecule that powers all the work of cells.

The reciprocal process of photosynthesis is called respiration. Cellular respiration actually "burns" glucose for energy. However, it doesn't produce light or intense heat as some other types of burning do. This is because it releases the energy in glucose slowly, in many small steps. The net result of this process is that sugar is broken down by oxygen into carbon dioxide and water. Cellular respiration involves many chemical reactions, which can be summed up with this chemical equation:

Evaporation, Sublimation, and Transpiration

The sun is the driving force behind the water cycle. It heats oceans, lakes, and other bodies of water, causing water to evaporate from the surface and enter the atmosphere as water vapor. Water in soil also evaporates easily. In addition, the sun heats ice and snow, causing it to turn directly into water vapor in the process of sublimation. Water also evaporates from the above-ground parts of plants. Transpiration is another process by which plants lose water. Transpiration occurs when stomata in leaves open to take in carbon dioxide for photosynthesis and lose water to the atmosphere in the process.

water cycle and climate

The water cycle plays an important role in climate. For molecules of liquid water to change to water vapor, kinetic energy is required, or the energy of movement. As faster-moving molecules evaporate, the remaining molecules have lower average kinetic energy, and the temperature of ocean water thus decreases. The primary way that oceans slow global warming is by heat uptake which warms ocean water and removes some energy from the atmosphere.

carbon leaves the atmosphere

There are also several different ways that carbon leaves the atmosphere. Carbon dioxide is removed from the atmo- sphere when plants and other autotrophs take in carbon dioxide to make organic compounds during photosynthesis or chemosynthesis. Carbon dioxide is also removed when ocean water cools and dissolves more carbon dioxide from the air. Because of human activities, there is more carbon dioxide in the atmosphere today than in the past hundreds of thousands of years. Burning fossil fuels and producing concrete has released great quantities of carbon dioxide into the atmosphere. Cutting forests and clearing land has also increased carbon dioxide into the atmosphere because these activities reduce the number of autotrophic organisms that use up carbon dioxide in photosynthesis. In addition, clearing often involves burning, which releases carbon dioxide that was previously stored in autotrophs.

Plants are the most important photoautotrophs in land-based, or terrestrial, ecosystems.

There is great variation in the plant kingdom. Plants include organisms as different as trees, grasses, mosses, and ferns. Nonetheless, all plants are eukaryotes that contain chloroplasts, the cellular "machinery" needed for photosynthesis.

pyramid of energy

This pyramid shows the total energy stored in organisms at each trophic level in an ecosystem. Starting with primary consumers, each trophic level in the food chain has only 10 percent of the energy of the level below it. The pyramid makes it clear why there can be only a limited number of trophic levels in a food chain or web.

Rain that falls on land may either soak into the ground, which is called infiltration, or flow over the land as runoff. Snow that falls on land eventually melts, with the exception of snow that accumulates at high altitudes or near the poles. Like rain water, snowmelt can either infiltrate the ground or run off.

Water that infiltrates the ground is called groundwater. Groundwater close to the surface can be taken up by plants. Alternatively, it may flow out of the ground as a spring or slowly seep from the ground into bodies of water such as ponds, lakes, or the ocean. Groundwater can also flow deeper underground. It may eventually reach an aquifer. An aquifer is an underground layer of water-bearing, permeable rock. Groundwater may be stored in an aquifer for thousands of years. Wells drilled into an aquifer can tap this underground water and pump it to the surface for human use. Runoff water from rain or snowmelt eventually flows into streams and rivers. The water is then carried to ponds, lakes, or the ocean. From these bodies of water, water molecules can evaporate to form water vapor and continue the cycle.

energy in ecosystems

When it comes to energy, ecosystems are not closed. They need constant inputs of energy. Most ecosystems get energy from sunlight. A small minority get energy from chemical compounds. Unlike energy, matter is not constantly added to ecosystems. Instead, it is recycled. Water and elements such as carbon and nitrogen are used over and over again.

Trophic Levels and Biomass

With less energy at higher trophic levels, there are usually fewer organisms as well. Organisms tend to be larger in size at higher trophic levels, but their smaller numbers result in less biomass. Biomass is the total mass of organisms at a trophic level.

Glucose,

a carbohydrate, is an organic compound that can be used by autotrophs and other organisms for energy. As shown in Figure below, photoautotrophs include plants, algae, and certain bacteria.

Photoautotrophic bacteria, called cyanobacteria,

are also important producers in aquatic ecosystems. Cyanobacteria were formerly called blue-green algae, but they are now classified as bacteria. Other photosynthetic bacteria, including purple photosynthetic bacteria, are producers in terrestrial as well as aquatic ecosystems.

Nutrient cycles

are important ecosystem processes that release matter necessary for life back into the environment, and that help sustain natural processes. Human actions are now negatively affecting many of these cycles.

Phototautotrophs

are organisms that use energy from sunlight to make food by photosynthesis.

Algae

are photoautotrophs found in most ecosystems, but they generally are more important in water-based, or aquatic, ecosystems. Like plants, algae are eukaryotes that contain chloroplasts for photosynthesis. Algae include single-celled eukaryotes, such as diatoms, as well as multicellular eukaryotes, such as seaweed.

Alcoholic fermentation

is carried out by yeasts and some bacteria. It is used to make bread, wine, and biofuels. Have your parents ever put corn in the gas tank of their car? They did if they used gas containing ethanol. Ethanol is produced by alcoholic fermentation of the glucose in corn or other plants. This type of fermentation also explains why bread dough rises. Yeasts in bread dough use alcoholic fermentation and produce carbon dioxide gas. The gas forms bubbles in the dough, which cause the dough to expand. The bubbles also leave small holes in the bread after it bakes, making the bread light and fluffy. Do you see the small holes in the slice of bread in Figure 6.14?

Chemosynthesis

is the process by which carbon dioxide and water are converted to carbohydrates. Instead of using energy from sunlight, chemoautotrophs use energy from the oxidation of inorganic compounds, such as hydrogen sulfide (H2S). Oxidation is an energy-releasing chemical reaction in which a molecule, atom, or ion loses electrons.

Photosynthesis

is the process by which carbon dioxide and water are converted to glucose and oxygen, using sunlight for energy.

Five Laws of Ecology According to Barry Commoner, there are Four Laws of Ecology (as follows). Explain how his laws govern the way nature works.

• Everything is connected to everything else. Simple put, we are living on large global system. It is a closed system, at least until we figure out how to get natural resources from other planets. Much like your body is an interconnected system of small systems, all networked together to work in harmony. The Earth is the same. Affect the Oceans dramatically in one place and it could affect other parts of the Earth. Deforestation in one area could affect the water cycle in other regions. Everything is connected. • Everything must go somewhere. Where does your garbage go? Imagine how much you throw away. What happens to it? Who or what does it affect? When you pour something down the drain of your home, where does it go? Nature has complex systems that help break down matter into its smallest components so that more life may use them. Humans, though, create a lot of non-biodegradable items that go into the environment. Everything a human creates must, at some point, go somewhere. Where? • Nature knows best. Billions of years have created the complex, intricate, and amazing ecosystem services, good, resources, and systems that humans rely upon for life and food. • There is no such thing as a free lunch. Nothing is free. As you learned in the chapter about energy: energy is neither created nor destroyed. It just changes shape. Nothing is free, and nothing can be created out of nothing. • Everything has limits. No natural resource or energy source is limitless. We are using renewable natural resources at rates faster than they can replenish themselves, deteriorating our land through erosion, emptying our water reservoirs, and depleting non-renewable resources.

When organisms die, they leave behind energy and matter in their remains. Decomposers break down the remains and other wastes and release simple inorganic molecules back to the environment. Producers can then use the molecules to make new organic compounds. The stability of decomposers is essential to every ecosystem. Decom- posers are classified by the type of organic matter they break down:

• Scavengers consume the soft tissues of dead animals. Examples of scavengers include vultures, raccoons, and blowflies. • Detritivores consume detritus—the dead leaves, animal feces, and other organic debris that collects on the soil or at the bottom of a body of water. On land, detritivores include earthworms, millipedes, and dung beetles (see Figure 6.8). In water, detritivores include "bottom feeders" such as sea cucumbers and catfish. • Saprotrophs are the final step in decomposition. They feed on any remaining organic matter that is left after other decomposers do their work. Saprotrophs include fungi and single-celled protozoa. Fungi are the only organisms that can decompose wood.