BIO 110 Exam #3 T/F

Among animal phyla, only worms and arthropod larvae (like caterpillars) show a "tube-within-a-tube" body plan.

FALSE. A tube-within-a-tube design describes an animal's body plan in which the outer tube is the body wall and the inner tube is the digestive tract from mouth to anus. Other tissues and organs are often located between the tubes. The tube-like shape of the body is most obvious in worms and worm-like larval phases such as caterpillars, but nearly all the bilateral animals (including humans) are tube-within-a-tube organisms.

A two-way digestive tract is more efficient than a one-way digestive tract.

FALSE. A two-way tract (also called an incomplete tract) is one in which there is only one opening into the body. Food goes into the body through this opening, is digested, and then the undigestable waste is excreted out of the same opening. A one-way tract (complete tract) has two openings, one for ingestion (mouth) and one for excretion (anus). It is more efficient in terms of the amount of nutrition that can be assimilated from food per unit time because the animal can eat and excrete continuously rather than having to stop feeding periodically to excrete waste through the single opening.

All modern animal phyla except two evolved first in the sea.

FALSE. All modern animal phyla evolved first in the sea. Only two of the phyla (Arthropoda, Chordata) have members that have made a complete transition to terrestrial environments (i.e., they can complete their entire life cycle outside of water or moist habitats).

Most animals show some degree of radial symmetry.

FALSE. Animals can have one of three types of body symmetry: (1) asymmetry, in which the body is irregular in form and cannot be divided into two identical halves by any plane, (2) radial symmetry, like a wheel, in which multiple planes can divide the body into identical halves, and (3) bilateral symmetry, in which only one plane can divide the body (left vs. right) into two identical halves. Only phyla in the Radiata lineage (Cnidaria, Ctenophora) and one phylum in the Bilateria (Echinodermata) show radial symmetry.

Bacteria cannot move very fast because they are so small.

FALSE. Bacteria are so small that they cannot cover much absolute distance per unit time when measured at our scale. But at their scale, bacteria can be very fast. Some measurements suggest bacteria powered by flagella can move 60 times their body length per second which, translated to human scales, would mean a 6-foot tall swimmer zipping through the water at 245 mph.

Cadherins are responsible for the movement of cilia in some protists.

FALSE. Cadherins are a group of proteins that function in modern animals to bind cells together in tissues. They are not responsible for cilia movement in protists. They may have been involved in the evolution of multicellular animals from colonial choanoflagellate protists since the latter also have cadherin proteins.

Cnidarians have a special type of mesoderm called the mesoglea.

FALSE. Cnidarians (jellyfish and anemones) are diploblastic, having only two tissue layers, an endoderm and an ectoderm. They do not have the third tissue layer that bilateral animals have, the mesoderm. The Cnidarians do have a jelly-like substance between the endoderm and ectoderm called the mesoglea, which serves as a hydrostatic skeleton. But it is not a tissue layer.

Ecdysis is a key to understanding major distinctions with the Parazoa.

FALSE. Ecdysis ("molting") is a particular kind of growth trajectory in which a bilateral animal sheds an outer body layer or exoskeleton that has become too confining in order to grow larger and enter later developmental phases (such as sexual maturation). It is exhibited by animal phyla (Nematoda, Arthropoda) within the group of protostomes called the Ecdysozoa, and separates them from all other animal groups, including Parazoa (sponges).

Because prokaryotes are so different from eukaryotes, it is thought that eukaryotic cells must have evolved from non-prokaryotic ancestors.

FALSE. Eukaryotic cells are indeed very different from prokaryotic cells in their average size and the variety of their internal structures and cellular organization. The differences could be taken to suggest that eukaryotes originated and evolved completely independently from the prokaryotes. But the prokaryotes evolved first, and many lines of evidence make it clear that they evolved from prokaryotic ancestors in the Bacteria or Archaea domains.

The first vertebrates to have jaws and lungs were amphibians.

FALSE. Fish evolved jaws and lungs before any other vertebrates, including the amphibians. Jaws evolved from gill arch supports and first appeared in an ancient group of fishes called the placoderms. Primitive lungs evolved later in freshwater ray-finned fish (in the Osteichthyes) that lived in habitats that were either shallow or prone to seasonal drydown and where their gills could not supply enough oxygen. The would come to the surface of the water and gulp air down into the lung where oxygen could diffuse into the body.

The Cretaceous is the "age of the gymnosperms".

FALSE. Gymnosperms evolved before the angiosperms and were the dominant seed plants during the late Paleozoic (approximately 299-145 mybp). Angiosperms (flowering plants) first appeared ~145 mybp and underwent a major adaptive radiation in the Cretaceous period which led to them displacing gymnosperms as the dominant seed plants over most of the earth. So the Cretaceous is the "age of the angiosperms".

Isogamy refers to mating between similar protist species.

FALSE. Isogamy means gametes that look alike and cannot be distinguished in terms of being male (sperm) or female (egg). They are typically the same size and both have one or more flagella. Isogamy is common in protists and is found in some other eukaryotes. Two other forms of gamete occurrence evolved first in the protists, anisogamy (both gametes have flagella but one is larger than the other) and oogamy (the larger gamete has no flagella and is considered to be the egg while the smaller gamete retains the flagella and is the sperm).

The ancestors of amphibians, lobe-finned fishes, are known only from the fossil record.

FALSE. Lobe-finned fishes are ancient bony fish whose fins had bones and muscles which are thought to have aided them in their locomotion across the sea bottom. The did give rise to the amphibians, which took the lobe-fins and evolved them into stronger legs for locomotion on land. The vast majority of the lobe-finned fishes are extinct. However, the coelacanth (a "living fossil") still survives in deep waters east of Africa. It is remarkably similar to extinct lineages and is thus considered a "living fossil". In addition, several species of lungfishes are found in Africa and Asia, and they also have lobed fins for locomotion out of water.

Mammals first evolved after the dinosaurs went extinct at the end of the Cretaceous period.

FALSE. Mammals evolved from mammal-like reptilian ancestors (synapsids and therapsids) before the dinosaurs appeared and then existed alongside the dinosaurs during the Mesozoic Era. But the dinosaurs dominated most vertebrate terrestrial niches. So the mammals were thus smaller, less abundant, and less diverse until the end-Cretaceous extinction eliminated most of the dinosaurs and allowed the surviving mammals to undergo a major adaptive radiation in the Cenozoic Era.

Incomplete metamorphosis occurs when an arthropod does not complete its life cycle.

FALSE. Many animal phyla show distinctive stages in the development of juveniles into adults. But this is most pronounced in the Arthropoda, which show two kinds of metamorphosis, Incomplete metamorphosis (such as in grasshoppers) occurs when the juvenile looks like miniature adult and mostly just grows in size, with some minor changes in body proportions. Complete metamorphosis (such as in flies or butterflies) occurs when the juvenile has a very different body plan compared to the adult. This usually involved eggs hatching into larva which grow and then enter a resting pupal phase, during which the juvenile body is re-organized to become the adult.

In plants, the daughter cells produced by meiosis are gametes.

FALSE. Meiosis does not always produce gametes. The only thing that is universal about meiosis is that it produces haploid daughter cells from a diploid parent cell. In most animals, including humans, the daughter cells are indeed gametes that fuse to form the diploid zygote. The phase of plant life cycles that undergoes meiosis is called the sporophyte and the haploid daughter cells are called spores. They develop into the multicellular haploid gametophyte phase. Eventually, some of the haploid gametophyte cells differentiate into gametes, and fertilization then occurs to produce a zygote. The zygote undergoes mitosis to restore the sporophyte phase.

Meristems increase lateral growth of plants whereas cambiums extend the length of stems and roots.

FALSE. Meristems are regions of continual cell division in land plants that elongate stem and root axes, including the production of new branches. This kind of growth is called primary growth. Cambiums are circular sheaths of cells in the stems and roots of plants that produce secondary growth, lateral thickening of stems and roots, by adding new layers of vascular tissue (xylem and phloem) periodically. This produces the wood in woody plants.

Mollusks offer the longest and most complete fossil record of all animals because their bones preserve very well.

FALSE. Mollusks (bivalves, snails, squids, octopi) are an ancient phylum that appeared early in animal evolution and have been important marine organisms throughout the Phanerozoic. They do have an extensive fossil record because many of them have hard exoskeletons made of calcareous shells, not bone.

Only bilateral animals have a nervous system.

FALSE. Most bilateral animals do have nervous systems that show increasing sophistication and specialization over evolutionary time, starting with simple nervous systems in the flatworms (phylum Platyhelminthes) and leading to highly advanced systems in phyla like the Mollusca, Arthropoda, and Chordata. However, some radial animals like Cnidaria (jellyfish and anemones) and Ctenophora (comb jellies) have nerve nets that serve as simple nervous systems without any centralized ganglia or brains.

Flowering plants first appeared after the dinosaurs became extinct.

FALSE. Most of the dinosaurs went extinct 65 million years ago at the end of the Cretaceous period when an asteroid struck the earth. Flowering plants first appeared about 145 million years ago and evolved alongside the dinosaurs.

Prokaryotes exchange genes through primitive sexual reproduction.

FALSE. Prokaryotes (bacteria and archaea) reproduce asexually. They do not engage in sexual reproduction. But they can exchange some DNA/genes through three mechanisms: (1) transformation, which is direct absorption of DNA from the surrounding environment, (2) transduction, when viruses transfer genes from one bacterium to another, and (3) conjugation, in which two bacterial cells connect and one of them sends copies of some genes (as plasmids) to the other cell in a one-way flow.

Protists are the most nutritionally diverse kingdom in terms of energy and carbon acquisition.

FALSE. Protists are one of the recognized kingdoms, and they do show a wide range of types of resource acquisition. But in terms of the fundamental question of how they get their energy and carbon (C-C bonds), they exhibit only two of the four possible combinations - photoautotrophy and chemoheterotrophy. Bacteria show all four strategies and are thus the most diverse. [See #7 on the previous LOSG for the details.]

The protostome phylum that is most closely related to vertebrates contains starfish.

FALSE. Protostomes and deuterostomes are the primary breakdown within the bilateral animals. They are distinguished by several key differences in the early development of embryos. Vertebrates are deuterostomes that belong to the phylum Chordata. The phylum Echinodermata includes the starfish and sea urchins. They are also deuterostomes and they are the closest relatives of the Chordata among the four deuterostome phyla.

Seeds evolved for dispersal while fruits evolved for protection of the embryo.

FALSE. Seeds (a plant embryo surrounded by stored food and protected by an external seed coat) evolved to protect the embryo and to nourish it before and during germination. Fruits (a ripened ovary surrounding one or more seeds) evolved specifically for seed dispersal, either to transport seeds directly (such as by wind) or to attract animals that will feed on the fruits and disperse the seeds simultaneously.

The Chondrichthyes are an important transition group between the reptiles and amphibians.

FALSE. The Chrondrichthyes are the cartilaginous fish (sharks and rays), and thus are not transitional between the amphibians and the reptiles. They are vertebrates, but their skeletons are not made of bone. They are descendants of ancient jawed fish that had bony plates in their skin but also did not have a mineralized backbone.

Metameric organization of the body first appears in the flatworms (Platyhelminthes).

FALSE. The Platyhelminthes are the flatworms, but they are not segmented. Segmentation first appears in the Annelida, another phylum of worms. The segments are repeated modular units of the body called metameres that can be specialized for different functions (as in the arthropods).

The angiosperms are called the flowering plants because of their petals.

FALSE. The angiosperms (phylum Anthophyta) are the flowering plants, and most of the flowering plants do have petals. But the term "flower" actually refers to the ovary, layers of tissues that evolved to surround the developing seed(s), provide some protection during development, mature into the fruit, and aid in seed dispersal.

Rotifers are an especially advanced group of annelids.

FALSE. The annelids are the segmented worms that belong to the phylum Annelida. Rotifers belong to the phylum Rotifera and are not work-like in their body plan. Both phyla belong to the Lophotrochozoa group of protostome animals.

A major trend in land plant evolution is the increasing dominance of the gametophyte in the life cycle.

FALSE. The life cycle of land plants includes both gametophytes, which produce gametes from already haploid tissues, and sporophytes, which produce haploid cells (spores) by meiosis. Both phases are multicellular. The gametophyte phase dominates (in terms of size and duration) the life cycle of the green algae ancestors of the land plants as well as living non-vascular plants like the Bryophyta (mosses). But the sporophyte gradually became more dominant as vascular and then seed plants evolved. A fern (Pteridophyta), pine tree (Coniferophyta, gymnosperm), and a tulip are all sporophytes, for example. So the overall trend is toward greater sporophyte dominance.

The oldest known multicellular fossils are from the Archaean eon.

FALSE. The oldest fossils of living cells are from 3.3 billion years ago, during the Archaean. But they were unicellular. Multicellular organisms do not appear in the fossil record until much later, about 700 million years ago, which is during the Proterozoic Eon.

Chordates are the only deuterostomes with skeletons.

FALSE. The phylum Echinodermata (starfish and sea urchins) uses two types of skeletons. The primary support is a hydrostatic skeleton. But they also have mineralized plates in their skin that provide additional support and protection from abrasion or predation.

The secondary palate is an important feature of weight streamlining that enables birds to fly.

FALSE. The secondary palate is a semi-hard, flattened structure that separates the nasal passage from the oral cavity in mammals. Among the terrestrial vertebrates, only mammals have the secondary palate. It allows an increased efficiency of feeding and of gas-exchange because a mammal can breathe and chew at the same time whereas a reptile, bird, or amphibian has to breathe directly through the oral passageway and must therefore stop chewing in order to take in air. This reduces the total amount of nutrition that can be assimilated per unit time.

Life has existed on earth about 4.5 billion years.

FALSE. The solid earth is about 4.57 billion years old, but the earliest evidence of life (chemical) is from 3.8 billion years ago and the oldest fossils of cells are 3.6 billion years old.

Fishes dominated the Paleozoic Era, reptiles dominated the Cenozoic Era, and mammals have dominated the Mesozoic Era.

FALSE. The three eras of the Phanerozoic Eon, in order, are: Paleozoic, Mesozoic, and Cenozoic. Fishes were the dominant vertebrates of most of the Paleozoic, though reptiles and mammals did appear during this era. Reptiles, including the dinosaurs, dominated he Mesozoic Era (esp. the Triassic and Jurassic periods). Mammals did not undergo a major adaptive radiation until after the end-Cretaceous extinction eliminated most of the dinosaurs and began the Cenozoic Era. So among the vertebrates, mammals have dominated the Cenozoic.

The transitional links between reptiles and mammals are not very well understood.

FALSE. There are extensive fossil transitions between reptiles and mammals. The lineage that eventually developed into mammals split off from an ancestral reptile in the Paleozoic Era and developed independently from the rest of the reptiles that eventually included dinosaurs and birds. The line leading to mammals included the synapsids and therapsids, which were dominant taxa on land before the dinosaurs emerged, and the transitions from ancient reptile to synapsid to therapsid to mammal are well understood (e.g., how jaw bones in synapsids became inner ear bones in mammals).

There are no real disadvantages of multicellularity, which is why it evolved shortly after the appearance of single-celled organisms.

FALSE. There are several disadvantages of multicellularity, especially for organisms that show greater specialization of cell functions: (1) there has to be accurate genetic regulation of the development of a multicellular body from a zygote; (2) activity by the specialized portions of the organisms has to be carefully coordinated; and (3) unicellular organisms can occupy very small habitats and ecological niches that larger multicellular organisms cannot. The oldest fossilized cells date back to 3.3 billion years, and multicellular organisms (animals) do not appear in the fossil record until about 700 million years ago. So it took a very long time for multicellular organisms to appear after life fist evolved.

Archaea are ancient members of the Bacteria domain.

FALSE. There are three domains of life (the highest level in the current taxonomic system): Bacteria, Archaea, and Eukarya. The Bacteria and Archaea are both prokaryotes while the Eukarya are eukaryotes. But the Archaea are not classified within the Bacteria and so are not ancient members of the Bacteria domain.

Biologists currently argue that there are two kingdoms and five domains of life.

FALSE. There had been 5 kingdoms since the 1970's - Monera, Protista, Fungi, Plantae, Animalia. But biologists then determined there are three domains that are above the level of kingdom in the taxonomic system - Bacteria, Archaea, and Eukarya. Four of the five kingdoms fall within the Eukarya. However, what had been one prokaryotic kingdom - the Monera - is now split between by two higher-level domains (a taxonomic impossibility).

Endothermy is better than exothermy.

FALSE. There is no universal advantage of endothermy over exothermy. Endothermy (internal generation of hear via metabolism) maintains a higher body temperature than the surrounding environment in most terrestrial habitats and thus allows endotherms to be active during colder times or in colder habitats. This can be a tremendous advantage over exotherms which mostly absorb heat or radiation from their surroundings to stay warm and cannot be nearly as active in cold times and places (if at all - they may have to go into torpor or dormancy to survive). But endothermy comes at a steep price. Per unit body mass, endotherms have to consumer 10 times more energy than exotherms, and there may not be enough food to satisfy this demand. So exotherms sometimes have the advantage over endotherms.

Vertebrates are the most successful phylum of the chordates.

FALSE. Vertebrates are not a phylum, but rather one sub-phylum of the phylum Chordata. They have been extremely successful in achieving both wide diversity and abundance in both aquatic and terrestrial habitats, certainly more so than the other chordate sub-phyla (Urochordata, Cephalochordata). It could be argued that the phylum Arthropoda (especially the insects) has been equally successful on land if measured by diversity and abundance.

Index fossils are those for which precise dates have been determined using radiometric methods.

False. Index fossils are fossils that are consistently found in specific rock strata and can thus be used as reliable indicators for those strata (this was one of William Smith's key observations). The law of superposition says that higher strata in a sequence of sedimentary rocks are younger than lower strata (unless faulting has overturned the original sequence). This principle means that relative dating - determination of older versus younger without measuring the actual age - of fossils, including index fossils, can be done. Radiometric dating (using radioactive decay of certain elements) is a form of absolute dating in which the actual chronological age of a rock sample and the fossils in it are determined.

The formation of Pangaea may have contributed to a mass extinction event during the Cambrian period.

False. None of the five mass extinction events recorded in the fossil record during the Phanerozoic eon occurred during the Cambrian. The Permian extinction was the greatest mass extinction of all time. It occurred at the end of the Paleozoic Era, and several factors are thought to have been involved. Massive increases in volcano activity (e.g., the Siberian Traps) altered the atmosphere and caused significant mortality. But continental drift also led to the coalescence of the "supercontinent" Pangaea. This had two consequences. First, the total geographic extent of shallow marine habitat near continental margins was reduced considerably, leading to large losses of marine diversity. Second, continental interiors are generally colder and drier than the continental margins near oceans, so the climate also became more stressful for terrestrial organisms.

The Late Quaternary extinction is well-documented in the fossil record.

False. The Later Quaternary Extinction (LQE) has happened over the last several centuries and it has been caused by humans through several activities. The extinction is ongoing and the evidence for it is in our own written records, not in the fossils.

The background extinction rate in the fossil record is in the range of about 300 families per million years.

False. The background extinction rate refers to periods of "normal" rates of extinction between mass extinction episodes. Background extinction rates measured in the marine invertebrate record are < 10 families per million years.

Earth's history is divided into four eons, each of which has lasted at least a billion years, and three of which have included living organisms.

False. There are four eons in the following order from oldest to youngest: Hadean (before life), Archaean ("ancient" life), Proterozoic ("before animals"), and Phanerozoic ("visible animals"). The first cells evolved in the Archaean, so three eons have included life. However, neither the Hadean nor the Phanerozoic lasted/has lasted a billion years.

A temporal bias exists in the fossil record because older phylogenetic lineages have had longer periods of time in which to produce fossils.

False. There are four types of biases in the fossil record that make accurate reconstruction of evolutionary history more challenging. One of them is a temporal bias. But is it not because older taxa have had more time to evolve. Instead, younger fossils are more likely to be found for two reasons: (1) they are closer to the surface and (2) they are more likely to have remained intact because there has been less time for climate and geological processes (erosion, rock melting) to alter or destroy them.

Marine waters absorb so much radiation that the animal and plant ancestors that colonized the land benefitted by the exposure to brighter light.

TRUE or FALSE. It is true that water absorbs light that could be used in photosynthesis, and light therefore limits photosynthetic rates by individual organisms (e.g., algae) and by the entire aquatic ecosystem. So terrestrial organisms in open habitats would have been exposed to much greater quantities of photosynthetically useful light. However, the atmosphere allows much more intense radiation to penetrate to the ground, including not only high-energy visible light but also UV radiation, which are photodestructive (they cause cellular damage and potentially death). So terrestrial organisms had to evolve ways to avoid excessive exposure to damaging radiation.

Skeletons are composed of some sort of hardened substance, like chitin or bone.

TRUE or FALSE. Skeletons can be composed of hardened substances like chitin (the material from which arthropod exoskeletons are constructed) or bone (vertebrate endoskeletons). However, the statement could be interpreted as false because not all skeletons are "hard". The term "skeleton" means any type of body construction that provides support and assists with locomotion. Some skeletons are hydrostatic, in which fluid is enclosed under pressure inside the body or a portion of the body (like the mesoglea in jellyfish or the coelom in some bilateral animals). This provides flexible support for the entire body and some resistance to muscles that can then move the body and achieve locomotion.

All mollusks show a similar body plan.

TRUE or FALSE. The Mollusca (bivalves, snails, squids, octopi) show very different external morphology and anatomical variation. But they do all share three homologous body parts due to inheritance from a common ancestor - the foot, the mantle, and the visceral mass - that are modified in different ways in different mollusc groups.

Plants "stood up" off the ground (i.e. developed structural body support and grew vertically) to disperse their seeds.

TRUE or FALSE. The ancestors of land plants in the green algae did not have tissues that could support upright growth, so they would have only been able to spread across the ground. Land plants developed structural support systems to "stand up" for three reasons. First, ground surfaces experience greater temperature extremes (esp. high temps) than in the air off the ground. Second, as soon as some plants began to grow vertically, they were able to absorb most of the light for photosynthesis and cast shade on those plants below them. So competition for light led to greater and greater degrees of vertical growth, culminating in large trees. Finally, dispersal of gametes, spores, and seeds through the air is harder than in the water. Gravity pulls spores and seeds down through the air more effectively than the denser water, so releasing such reproductive structures from higher points off the grand became advantageous. The statement is partly true, but not completely so, and thus could be argued as either true or false.

Prokaryotes are the dominant forms of life on earth.

TRUE or FALSE. The answer could be argued either way, depending on how the word "dominant" is interpreted. Bacteria and Archaea are indeed the dominant forms of life in terms of total numbers of living organism present, total living biomass, and widest distribution across habitats and environments on earth. So the prokaryotes do dominate the "normal" functioning of earth's ecosystems. But "dominant" could mean the power of an organism or type of organism over the earth and the rest of life, including alteration, degradation, or destruction of nature. In this sense, it could be argued that one species (us) is the most dominant life form at this point in earth's history.

Gnathostomes include the ray-finned fishes and the amphibians.

TRUE or FALSE. The earliest vertebrates were primarily filter-feeders that did not have jaws (Agnatha). Gnathostomes are later vertebrates with jaws. The first gnathostomes were ancient fish (placoderms), and all other vertebrate groups descended from them, including the ray-finned fish (Osteichthyes), the cartilaginous fish (Chrondrichthyes), the amphibians, reptiles, birds, and mammals. So the statement could be considered true because the ray-finned fish and amphibians are gnathostomes. However, it could be judged false because they are not the only gnathostomes.

Chloroplasts and mitochondria are believed to be descended from free-living prokaryotes because they both possess some DNA.

TRUE or FALSE. The endosymbiotic theory says that mitochondria and chloroplasts were once free-living bacteria that were ingested by prokaryotic or eukaryotic host cells as food but then developed into a mutualistic relationship in which the symbiont provided energy and/or carbon for the host. The strongest evidence for this is that both mitochondria and chloroplasts have some active genes that contribute to their function, and DNA sequencing has shown that the genes are most closely related to certain types of bacteria. So the statement is true in this sense, but it could also be argued as false due to incompleteness since there are other types of evidence that support the theory including: (1) the organelles are similar in size to their bacterial ancestors, (2) they have internal membrane systems similar to some bacteria, (3) they have double membranes, due to having been enveloped by the original host's plasma membrane, and (4) some chloroplasts have multiple membranes from repeated ingestion events.

Sporophytes and gametophytes are different stages in the life cycle of ferns.

TRUE or FALSE. The statement is literally true, but it could imply that only ferns have both gametophytes and sporophytes. All land plants have both phases in their life cycles, not just the ferns, so in this sense the statement could be judged as false. [See the answer to #14 for an explanation of what gametophytes and sporophytes are.]

Respiratory uptake of oxygen by gas-exchange is easier on land than it is in the water.

TRUE or FALSE. The statement is partly true because the concentration of oxygen in the air (21%) is far greater than it is in water, so aerobic aquatic organisms face a much greater challenge in absorbing sufficient oxygen to stay alive, especially larger, multicellular organisms with lower surface-to-volume ratios. But it is also partly false because oxygen must always be absorbed through a moist surface - i.e., the absorbing cells or tissues cannot be dry - and maintaining a moist surface is very difficult when in contact with the dehydrating power of the air. So gas-exchange on land required internalization and protection of the gas-exchange surfaces (e.g., lungs had to evolve from gills).

Locomotion is harder on land than it is in the water.

TRUE or FALSE. The water is a denser medium than air, and this has two consequences for locomotion. First, water is more buoyant, so aquatic organisms are supported more by their medium in response to gravity, and thus spend less energy maintaining a vertical position in the water. This allows them to focus more of their energy toward forward movement. Terrestrial organisms face less friction/resistance in the less dense air, so in general they don't have to spend as much energy on forward movement. However, their bodies are pulled downward more efficiently by gravity. So if they do not have legs, they experience more intense friction in moving across the surface, and if they do have legs, they have to expend more energy to stay elevated above the ground to reduce friction.

Reptiles succeeded in becoming fully terrestrial (i.e. not requiring an aquatic habitat at any point in the life cycle) because they evolved the amniote egg.

TRUE or FALSE. This statement is mostly true because to be fully terrestrial means that you must be able to complete the entire life cycle, including successful reproduction of surviving offspring. The vertebrate ancestors of the reptiles, amphibians, cannot do this because their fertilized eggs are not protected by any outer layers and must remain in water to survive. The amniotic egg is the key innovation that allowed reptiles to escape confinement to the water for reproduction. Such an egg consists of an embryo surrounded by four membranes that serve different functions (including the amniotic sac). Some amniotes (reptiles, bird) add a secreted leathery or mineralized shell beyond these membranes so the egg can be laid and develop outside the body. The vast majority of the mammals, on the other hand, retain the amniotic egg internally.

The endosymbiotic theory accounts for important steps in the evolution of eukaryotic cells.

TRUE. "Endosymbiosis" means "living together inside". It refers to a widely accepted theory that two key organelles in eukaryotes - mitochondria and chloroplasts - were once free-living bacteria that were ingested by prokaryotic or eukaryotic host cells as food. But digestive breakdown was short-circuited by mutations in the host, and the ingested bacterium because an internal symbiont of the host. The symbiosis eventually developed into a mutualism in which the symbiont provided energy and/or carbon for the host. These organelles are not the only innovations that led to eukaryotic cell organization, but they played a key role.

Molecular biologists are fairly sure we will never be able to determine who LUCA was.

TRUE. "LUCA" stand for "Last Universal Common Ancestor" and refers to the hypothetical ancestor of all life on earth. It would have to be a very ancient type of prokaryote that gave rise to the three domains of life and eventually all the diversity within those domains. In principle, DNA sequencing and phylogenetic reconstruction might be able to tell us what that ancestor was like, at least genetically. However, prokaryotes and eukaryotes engaged in a tremendous amount of lateral gene transfer - one-way or two-way movement of DNA between cells unrelated to reproduction - for billions of years after live evolved. This obscures what would otherwise be traceable genetic lineages and makes it impossible to go all the way back and identify what kind of cell LUCA was.

Secondary endosymbiosis is thought to have resulted in some organelles with four membranes, including chloroplasts.

TRUE. (See the answer to #7 for the basics of the endosymbiotic theory). Primary endosymbiosis is when the free-living cell ingested by the host is a prokaryote, whereas secondary endosymbiosis occurs when the host ingests a eukaryotic cell. Chloroplasts show both type of endosymbiosis among the photosynthetic groups that have them. Primary endosymbiosis occurred when free-living photosynthetic bacteria (cyanobacteria) were ingested. This cell then because a free-living photosynthetic eukaryote with an internal symbiont that was double-membraned. When this eukaryote was ingested by another such cell, the chloroplast ended up with four membranes.

Some organisms classified as animals do not have true tissues.

TRUE. All animals are multicellular, with some degree of specialization in cell functions. But not all animals have tissues (sets of cells that work together for a specific function. The animal kingdom is thus divided into two major groups - those without tissues (Parazoa, the sponges) and those with true tissues (Eumetazoa, everyone else).

All organisms can be classified into four categories on the basis of how they acquire energy and carbon.

TRUE. All organisms get energy either from radiation (photo-) or from breaking down chemical bonds (chemo-). They get their carbon (specifically C-C bonds) either by synthesizing them out of simple inorganic molecules like CO2 (autotrophs) or by breaking down more complex organic molecules (heterotrophs). All four combinations of these strategies exist: (1) photoautotrophs, (2) photoheterotrophs, (3) chemoautotrophs, and (4) chemoheterotrophs. Bacteria show all four strategies. Plants and some protists are also photoautotrophs. Animals, fungi, and some protists are also chemoheterotrophs.

In terms of energy and carbon acquisition, the kingdom that shows the greatest range of abilities is Monera.

TRUE. All organisms get energy either from radiation (photo-) or from breaking down chemical bonds (chemo-). They get their carbon (specifically C-C bonds) either by synthesizing them out of simple inorganic molecules like CO2 (autotrophs) or by breaking down more complex organic molecules (heterotrophs). All four combinations of these strategies exist: (1) photoautotrophs, (2) photoheterotrophs, (3) chemoautotrophs, and (4) chemoheterotrophs. Plants and some protists are also photoautotrophs. Animals, fungi, and some protists are also chemoheterotrophs. But bacteria show all four strategies. So bacteria (as classified in the kingdom Monera) do indeed show the greatest diversity in terms of energy and carbon acquisition.

A colonial organism is different from a multicellular organism, at least in the way that biologists use these terms.

TRUE. Both types of organisms consist of more than one cell. But a multicellular organism shows some degree of specialization in cell functions (even if there are clearly recognizable tissues or organs), whereas a colonial organism does not show such specialization - it is simply an aggregation of mostly independent cells that does benefit in some way from the association.

Radially symmetric animals show little to no cephalization.

TRUE. Cephalization means the development of a distinctive head region in a bilateral animal, where sensory organs, centralized neural processing, and feeding structures are typically located. These features are consistent with a bilateral organism that moved forward through the environment in the search for suitable habitat and food. Asymmetric animals (Parazoa, sponges) and radially symmetric animals (Cnidaria, jelly fish and anemones; Ctenophora, comb jellies) to not show any noticeable cephalization, even though they can move in particular directions.

Chitin is especially common among the Ecdysozoa.

TRUE. Chitin is a semi-rigid complex carbohydrate that is found extensively in the Arthropoda. It is the material from which arthropod exoskeletons are made. The bilateral animals are divided into the Protostomes and Deuterostomes on the basis of early developmental patterns, and the Protostomes are in turn divided into the Ecdysozoans and Lophotrochozoans which are distinguished by the occurrence of ecdysis (molting of an external body layer) and specialized feeding structure (lophophore) and particular larval type (trochophore). The arthropods belong to the Ecdysozoa.

Choanoflagellates may have been involved in the evolution of multicellular animals.

TRUE. Choanoflagellates are ancient heterotrophic colonial protists that still have some living descendants today. The simplest recognized animals are the Porifera (sponges), which are multicellular organisms with some cell specialization but no true tissues. The feeding cells of sponges (choanocytes) are strikingly similar in structure and function to choanoflagellate cells. This, plus DNA sequencing data suggest that choanoflagellates are the closest relative to the primitive animals.

Most living plant species are embryophytes.

TRUE. Embryophytes are plants that retain their embryos on or inside the parent plant for protection and nourishment until they are dispersed as offspring. All land plants are embryophytes, so they are by definition the most diverse living plant species.

Oxygen is both very dangerous and very beneficial for living cells.

TRUE. Molecular oxygen (O2) is very reactive chemically and will damage molecules in cells by oxidation (stripping away electrons). This is the same kind of reaction as rusting and burning. So O2 is a very dangerous (lethal) molecule inside cells unless its presence can be controlled very carefully. But some cells evolved the ability to use the reactive nature of oxygen to increase the efficiency of cellular respiration by a factor of 19-fold. So a former poison was transformed into a chemical ally in the aerobic organisms.

Mosses are analogous to amphibians in their dependence on watery habitats.

TRUE. Mosses belong to the phylum Bryophyta. They are non-vascular plants that are typically found in moist or watery habitats for two reasons. First, they do not have efficient roots for absorbing and transporting water to the stem and leaves, so the entire plant needs to absorb water directly from the environment. The second reason is that their sperm are flagellated and must swim through water (at least a thin film) to reach and fertilize the egg. Amphibians are restricted to moist habitats since they do not have efficient lungs and must absorb some of their water through their moist skins. They are also restricted to aquatic habitats for reproduction. The eggs have thin outer membranes that do not protect them from dehydration. So the eggs have to be laid in water and the juvenile phases (like tadpoles) are restricted to water until they develop the ability to breath out of the water.

Mycorrhizae may have been involved in the early stages of plant colonization of the land.

TRUE. Mycorrhizae are fungi that live in symbiotic relationships with the root systems of most land plants. They provide nutrients for the host plant and receive carbohydrates from the host. The first algae that colonized the land did not have true roots with vascular transport tissue, so acquiring water and nutrients from the soil was very difficult. Symbiotic fungi may have made the transition easier, and there is some fossil evident that supports the close association of fungi with early plants.

Protists were the first organisms on earth to reproduce sexually.

TRUE. No prokaryotes reproduce sexually - i.e., through haploid cells (gametes or nuclei) that fuse to form a diploid offspring cell. True sexual reproduction arose first in the protists, and they show a wide range of life cycles in which the haploid and diploid phases differ in their roles and dominance.

Metameres are parts of segmented bodies, such as in earthworms and humans.

TRUE. Numerous bilateral animal groups show segmentation of the body (also called metameric organization) in which repeated modular units (metamers) are build during development and then often specialized for particular functions in the adult organism. Earthworms (phylum Annelida), called the segmented worms, are classic examples. Arthropods (phylum Arthropoda) also show dramatic specialization of segmented bodies. And vertebrates (phylum Chordata) show pronounced segmentation of the backbone and in some other anatomical features (such as the abdominal region).

Prokaryotes play very important roles in ecosystem nutrient cycling.

TRUE. Nutrients normally cycle through ecosystems from the environment to autotrophs (like plants) to different consumers in the food web, into dead organic matter, and are finally returned to the environment through decomposition of the organic matter. Prokaryotes (especially in the domain Bacteria) play major roles in the decomposition since they are able to extract energy and nutrients from dead materials. One of the best examples is the nitrogen cycle, in which many different classes of bacteria are involved in chemical transformation. Some bacteria can also convert inorganic, unusable forms of nitrogen (N2 gas) into organic forms through nitrogen fixation, and thus increase the total amount of nitrogen in the ecosystem cycle.

Dehydration was the most dangerous challenge faced by marine animals and algae that colonized the land.

TRUE. Organisms that colonized the land faced numerous physical and chemical challenges for survival. But dehydration was the most important. Aquatic habitats, even the salty oceans, surrounds organisms in a watery medium that prevents dehydration and allows the exposure of tissues and organs like gills to the medium in order to absorb oxygen more efficiently. Reproduction cells (gametes, zygotes) and embryos do not have to be protected from dessication. But the evaporative power of the air is many orders of magnitude greater than the water and quickly kills unprotected cells, tissues, or organisms.

Phylogenetic reconstruction of the prokaryotes requires molecular tools.

TRUE. Phylogenetic reconstruction means building an evolutionary tree that accurately shows the relationships among ancestral and descendant taxa. The prokaryotes (bacteria and archaea) do show some differences in external morphology and internal cell structure that allows some classification and phylogenetic tree building. But DNA (or RNA) sequence data from widely shared genes are required to span the range of prokaryote diversity and determine trees for all prokaryote taxa.

Some deuterostomes show both radial and bilateral symmetry during their life cycle.

TRUE. Radial body symmetry occurs when an animal can be divided into two mirror image halves by more than one plane (like a wheel). Bilateral symmetry means the animal can only be divided in equal halves by one plane that runs down the midline of the body and separates the right and left halves. Radial versus bilateral symmetry is the most fundamental distinction within the animals that have true tissues, which includes the vast majority of animals. Some radial taxa (Cnidarians, jellyfishes) show a simple bilateral larval form during the life cycle but the adult form dominates the cycle and it is radial. Among all the bilaterals, only the deuterostome phylum Echinodermata (starfish and sea urchins) shows radial symmetry in the adult form. The juvenile phase is bilateral and then an unusual pattern of development results in the radial adult.

Ovules are to seeds as ovaries are to fruits.

TRUE. Seed plants produce reproductive structures (seeds) that are composed of an embryo surrounded by stored food and protected by an external layer (the seed coat). The seed develops from a juvenile stage called the ovule, where the egg is located prior to fertilization. The seed plants include the gymnosperms ("naked seed") which have no other tissue or covering surrounding the seed. But angiosperms ("vessel seed", the phylum Anthophya) have an additional tissue layer surrounding the seed called the ovary, which develops into the fruit. So ovules develop into seeds and ovaries develop into fruits.

Among the protostomes, only the Arthropoda have segmented appendages (esp. legs).

TRUE. Several of the protostome phyla - such as some segmented worms in the Annelida - have appendages that extend from the body and are used in locomotion. However, only the Arthropoda (crustaceans, insects, spiders, etc.) have segmented, jointed appendages that serve as efficient legs.

Stomata exist because of the cuticle.

TRUE. Stomata are regulatory pores in the epidermal layer of land plants. They open to allow carbon dioxide to enter for photosynthesis and close when necessary to prevent too much water loss. Stomata had to evolve because the aquatic ancestors of plants that colonized the land did not have a protective outer layer to prevent dehydration. The cuticle - a waxy coating secreted by the epidermis that covers the entire surface of the plant - evolved to prevent dessication. But it also prevents carbon dioxide absorption. So plants had to evolve a controlled way of getting carbon dioxide into the leaves without losing too much water. This is why stomata evolved, so they do exist because of the cuticle.

Some of the nematodes cause problems for humans.

TRUE. The Nematoda are the round worms. Many are free-living and not dangerous to humans. But two of the major groups (classes) of the nematodes are flukes and tapeworms which infect hundreds of millions of humans world-wide and cause extensive health impacts, including mortality.

Mammals, like reptiles, are amniotes.

TRUE. The amniotes are several major groups of terrestrial vertebrates (reptiles, birds, mammals) that share the synapomorphy of the amniotic egg. This form of offspring development evolved in terrestrial environments and freed them from having to reproduce in water, which was a major limitation of the amphibians. The amniotic egg consists of the embryo surrounded by four membranes that serve different functions in nurturing the embryo - the amnion, the chorion, the allantois, and the yok sac. Reptiles and birds add a leathery or mineralized shell beyond these membranes so that the egg can be deposited outside the body of the parent and develop further before hatching (ovipary). In contrast, nearly all mammals retain the amniotic egg with its four membranes inside the parent and produce their offspring through live birth (vivipary).

The presence or absence of a coelom distinguishes major groups within the animal kingdom.

TRUE. The coelom is found only in bilateral animals. It is a space between the outer body wall and digestive tract that some animals have. If the coelom is completely lined with mesoderm tissue, they are called coelomate. Other animals have a coelom but it is not completely lined with mesodermal tissue (pseudocoelomate), and finally some animals do not have a coelom at all (acoelomate). It used to be thought that these differences represented a gradual one-way change in evolution - i.e., that acoelomates gave rise to pseudocoelomates which in turn yielded coelomates. It is now know that this is not true, that the coelom probably arose very early in bilateral evolution and was then partially (pseudocoelomate) or completely (acoelomate) lost by different lineages at different times. So it is still an important body-plan distinction, but it plays a different role in animal phylogeny now.

Developmental genes may have contributed to rapid diversification during the Cambrian explosion.

TRUE. The earliest animal ancestors underwent a spectacular adaptive radiation (sometimes called the "Cambrian explosion") during the Cambrian period, starting 542 million years ago. Nearly all existing animal phyla (~35) had evolved by the end of the Cambrian. Three factors are thought to have contributed to the "explosion": (1) increased oxygen levels in the oceans, which supported higher metabolic rates and the synthesis of calcium carbonate, a hard mineral that could protect soft-bodied animals, (2) the appearance of the mesoderm, a third embryonic tissue layer which allowed the development of more complex bodies with specialized organ systems, and (3) the proliferation and diversification of the homeobox (Hox) developmental regulation genes, which along with the mesoderm led to more complex, capable bodies.

There are no seed-producing, nonvascular plants.

TRUE. The first land plants evolved from green algae ancestors. They do not have vascular tissue. They do produce zygotes through sexual reproduction, and the embryos remain attached to the parent until dispersal. But they do not make a seed, which is an embryo surrounded by stored food reserves and protected by a tough outer seed coat. Living phyla that are non-vascular and do not produce seeds include the Bryophyta (mosses). Vascular tissue then evolved before seeds. A living phylum that has vascular tissue but not seeds is the Pterophyta (ferns). Seeds evolved later within some of the vascular plants to give rise to "the seed plants", which include the gymnosperms (Coniferophyta) and angiosperms (Anthophyta).

Jaws probably evolved from gills.

TRUE. The fossil record and developmental regulation agree that vertebrate jaws (skeletal support with attached muscles for opening/closing) evolved from cartilaginous gill slit supports in ancestral, jawless vertebrates. These gill supports were used to keep the gill slits open for gas-exchange and filter feeding. Some of these supporting structures moved, enlarged, and fused to form the upper and lower jaws of the first jawed vertebrates (placoderm fish).

Planuloid organisms may represent an important shift from radial to bilateral symmetry in animal evolution.

TRUE. The planula larva is one phase in a Cnidarian (jelly fish) life cycle. The full life cycle has three phases: (1) adult, free swimming, radially-symmetrical, medusa stage that engages in sexual reproduction to produce a zygote, (2) a larval, free-swimming, bilateral phase that ultimately settles down onto the marine substrate, and (3) the adult, radially-symmetrical polyp phase that is anchored to the marine substrate and is immobile. Radial animals evolved before bilaterals, and one hypothesis for the origin of all the bilaterals is the planula stage of Cnidarians, which may have failed to develop into the mature polyp phase and remained a bilateral, free-swimming organism through a change in developmental processes called paedomorphosis.

Mammals are heterodonts.

TRUE. The term heterodont refers to "different teeth" in a vertebrate animal, meaning that the teeth are not the same size and shape and they are designed for different kinds of food processing, from grinding (molars) to shearing/cutting (premolars and incisors), to piercing (canines). Fish and reptiles are mostly homodonts ("same teeth"), with little to no differentiation among their conical teeth. The evolution of heterodont teeth was a major theme in the diversification of mammal diets and contributed substantially to their dominance of terrestrial habitats following the demise of the dinosaurs.

Invertebrates account for the majority of named species on earth.

TRUE. There are far, far more named invertebrates (animals without a vertebral column) than vertebrates in the world. Over 95% of all animals are parazoa or protostomes, including the incredibly diverse arthropods. The dominance by invertebrates would be even more dramatic if we had identified all living animal species on earth, since there are far more undiscovered invertebrates than vertebrates.

Coevolution between plants and animals has had a significant impact on plant evolution.

TRUE. There are three main ways plants have coevolved with animals and which have contributed to the diversification of both groups on land. First, many animals disperse plant gametes (pollination) and seeds, usually in return for some kind of food reward (nectar, fruit), and such partnerships are often very specific and necessary for the survival of both parties (mutualism). Second, many animals consume plant tissue (herbivory), fluids (sap-sucking), or offspring (seeds) as food sources. This required plants to defend themselves mechanically and chemically, which in turn forced animal consumers to evolve new ways of dealing with the defenses. Finally, plants often provide habitat structure in which or on which animals live, move, hide, hibernate, etc. This is a benefit for the animal without any particular benefit for the plan (commensalism).

No one knows at this point how many kingdoms of life there are.

TRUE. There had been 5 kingdoms since the 1970's - Monera, Protista, Fungi, Plantae, Animalia. However, what had been one prokaryotic kingdom - the Monera - is now split between two higher-level domains (Bacteria and Archaea), a taxonomic impossibility. Other discoveries suggest there may be more kingdoms within the Protista and within the Eukarya. So exactly how many kingdoms there are is now unclear.

Aerobic respiration evolved after photosynthesis.

TRUE. There was no free molecular oxygen (O2) in the atmosphere of the early earth. It did not start accumulating in the atmosphere until oxygen-producing photosynthesis evolved in some prokaryotes (cyanobacteria) about 3.3 billion years ago and did not reach levels near the modern 20% or so until 2.2 billion years ago. All living cells were necessarily anaerobic until the oxygen concentrations rose. At that point, some cells began to use oxygen in their cellular respiration pathway (the breakdown of food molecules to produce energy) and thus became aerobic organisms.

Some of the worm-like phyla have an incomplete digestive tract.

TRUE. Three of the animal phyla we studied are worm-like in their body plans. Two of them - Annelida, the segmented worms, and Nematoda, the roundworms - do have complete digestive tract composed of a mouth an anus. But the Platyhelminthes, the flatworms, have an incomplete digestive tract with only one opening that serves for both ingestion and waster excretion.

Totipotency helps plants cope with their sessile existence.

TRUE. Totipotency is the ability of a mature somatic cell, which has already differentiated into its particular functions, to revert to an earlier developmental phase and re-express genes that were turned off during development (like stem cells in animals). This allows a cell to produce new growth, including the possibility of generating a whole new organism from a single somatic cell without involving normal reproductive processes. This is the basis for tissue culture methods. Plants show much greater capabilities for totipotency than animals, and the main reason is that sessile (immobile) plants cannot escape their physical or biological environments and often must recover from physical or biological damage. Totipotency allows them to do so, increasing their odds for survival and future reproduction.

Most mammal species show vivipary.

TRUE. Vivipary is a form of reproduction in vertebrates, in which an offspring develops from a zygote inside the body of the parent and emerges as an intact organism without going through an independent egg stage. The vast majority of vertebrates, including extinct and modern forms of fish, amphibians, reptiles, and birds, deposit fertilized eggs outside the body, where they develop into a more advanced embryo before hatching (called ovipary). But nearly all modern mammals develop the young internally and deliver them as free-living offspring without hatching from an egg.

One of the factors thought to be responsible for mass extinction is bolides.

True. A bolide is a large extraterrestrial object (asteroid or comet) that strikes a planet. Vast numbers of bolides hit the earth during the early phases of its existence and influenced ancient life. But the clearest connection between bolides and extinction is the strong evidence for a large asteroid striking the earth and causing the Cretaceous extinction at the end of the Mesozoic Era 65 million years ago. This mass extinction caused the demise of the dinosaurs and catalyzed the accelerated evolution of mammals and birds.

The cichlids provide an impressive example of adaptive radiation.

True. Adaptive radiations are "bursts of speciation" - relatively rapid evolutionary diversification, in response to a geographic or biological adaptive zone, that produces numerous descendant taxa with a wide range of adaptive forms. Cichlids are a very diverse family of freshwater fish that have shown incredible diversification from a common ancestor in three large African lakes over the last 3-12 million years. They the most striking example of adaptive radiation among existing vertebrates.

Adaptive zones are important for adaptive radiation.

True. Adaptive zones are actually required for adaptive radiation. Adaptive radiations are "bursts of speciation" - relatively rapid evolutionary diversification, in response to a geographic or biological adaptive zone, that produces numerous descendant taxa with a wide range of adaptive forms. Adaptive zones come in two forms, geographic and biological. A geographic adaptive zone is an unoccupied habitat with available space and resources that can be colonized by organisms (such as volcanic islands rising out of the sea). A biological adaptive zone is a new structural or functional capability that arises by mutation and which allows organisms to exploit new resources or habitats.

The hypothesis of punctuated equilibrium questioned the longstanding assumption of Darwinian gradualism.

True. Darwin thought speciation would happen very slowly and thus take a very long time, up to millions of years. This has been called Darwinian gradualism. But if this were the case, the fossil record should show lots of transitional fossils form ancestor to descendant species since there has been so much time over which fossils could be preserved. However, extensive transitions are not all that common. In the 1970's two evolutionary biologists argued that Darwinian gradualism may be wrong, or at least that it wasn't necessary that all speciation events would be so slow. They based their ideas on other observations in the fossil record, particularly that there were often bursts of fairly rapid appearance of new species ("punctuations") and then long periods where there seemed to be little to no change in those species ("equilibrium"). They suggested that "punctuated equilibrium" often involved adaptive radiations and accounted for much more of the diversification of life than had previously been considered.

The worst mass extinction in the fossil record was the Permian extinction.

True. Higher percentages of marine and terrestrial and marine organisms became extinct during the end-Permian extinction event than during any of the other four mass extinction events during the Phanerozoic Eon. [see answer to #1 for details on factors that caused the Permian event]