SAT Biology E/M Subject Test

Part II: Subject Review

Chapter 14 Cracking Ecology

Ecology is the study of the interactions between organisms and their environments. The environment includes abiotic (nonliving) factors such as light, temperature, nutrients, and water, as well as biotic (living) factors such as other organisms that inhabit the environment. In this chapter we will see how groups of organisms interact with one another and how they interact with their environments.

Before we get into an in-depth discussion of ecology, let’s take a look at the levels of biological organization:

1.    Cell


2.    Tissue


3.    Organ


4.    Organism


5.    Population


6.    Community


7.    Ecosystem


8.    Biome


9.    Biosphere

We’ve already discussed many of these levels of biological organization (cells, tissues, organs, and organisms) in previous chapters. Let’s begin with the fifth level—population.


We’ve mentioned the term population before, but we never really defined it, so let’s do that now:

A population is a group of individuals in a particular area that interbreed and therefore share the same gene pool.

A population is sort of a subset of a species. Think about it this way: A species is a group of organisms that is able to interbreed, and a population is a group of organisms that is interbreeding. For example, a group of mice on the West Coast of the United States may belong to the same species as a group of mice on the East Coast of the United States, because if they were brought together, they could interbreed. However, because they are separated by such a great distance, they are NOT interbreeding and are NOT members of the same population.

Because a population consists of a group of organisms that are interbreeding, this is the level of organization at which evolution is seen.

Evolution does not act on an individual; individuals cannot evolve. But populations can evolve, as their individuals (and more important, their individuals’ offspring) undergo changes in phenotype and genotype.

Population Growth

There are two types of population growth you should be familiar with for the SAT Biology E/M Subject Test. The first is exponential growth, and the second is limited growth. The two types are related; a population that starts off growing exponentially will ultimately reach a level at which it is unable to sustain that rapid rate of growth, at which point growth becomes limited.

Consider a single bacterium. This bacterium can divide by binary fission to produce two bacteria. It takes the bacterium about 20 minutes to accomplish this, if all the conditions for growth are ideal. After another 20 minutes, both of the new bacteria would undergo binary fission, and we’d have four bacteria. After another 20 minutes, we’d have 8, then 16, and so on and so on and so on. After just one day—24 hours—we’d have more than 4 × 1012 bacteria. That’s 4,000 billion billion bacteria!

In this type of growth the size of the population increases exponentially, and if we graphed it, it would look like this:

Of course, in reality this could never happen. As the bacterial population continued to grow, nutrients would get used up, space would become scarce, and waste products would accumulate. Some members of the population would die, and the growth curve would flatten out as the population stabilized.

Here, the maximum population size is limited. The maximum population size that a particular environment can sustain is referred to as the carrying capacity.

The carrying capacity of an environment can change if the environment changes. For example, if we provide our bacterial population with a larger container and more food, the carrying capacity would increase to reflect this.

Suppose we had a field of grasses that could support a population of 100 mice. Suppose further that a drought reduced the number of grasses that could grow. The field may no longer be able to support all 100 mice. In this case, the carrying capacity of the field would decrease.


community is a group of populations that live in a particular environment. These populations can interact with one another in many different ways, including symbiotically, competitively, and predatorily but not reproductively. We already talked about symbiosis in Chapter 12, so we won’t cover that again. Instead, let’s talk about competition and predation.

Battling It Out

Technically, we’ve also already mentioned competition, when we talked about evolution in Chapter 9. We said that organisms that were more successful competitors would be better able to survive within their environment. What do we mean when we say “competitors”?

To understand competition fully, we have to introduce a new term: the niche. An organism’s niche is the way it lives in its environment, including its nesting behavior, what type of food it eats, and when it hunts. You can think of it like this: If an organism’s environment is its address, then its niche is its job.

If two populations have similar niches (for example, if they hunt the same food at the same time), there will be a lot of competition between the two populations. The two populations become competitors against each other for the food. Usually, one population will “win out” over the other (it will compete more effectively), and that population will grow in size (to its natural carrying capacity), while the other population will shrink. In extreme cases, the winning population will compete so effectively that it will drive the losing population out altogether. This allows the winning population to be the sole occupant of the niche.

Then What?

Well, we know from Chapter 9 that competition drives evolution. So what happens next is that the populations evolve. Generally, the winning population doesn’t have to evolve too much, because the members of the population can keep on doing what they’ve been doing—they’re now the sole owners of the niche. But the losing population has to find another way to survive. Obviously, trying to occupy the original niche was a failure. Perhaps some members of the losing population might begin hunting at a different time. This would allow them to be more successful, because the winning group is temporarily out of the picture. Over time, this would produce distinct differences in the populations’ hunting times, and they would occupy different niches.

Populations and Evolution: A Quick Summary

•   Populations occupy different niches within their environment.

•   If two populations have similar niches, they will compete for sole “ownership” of the niche. The more similar the niches, the more intense the competition.

•   The winning population retains the niche and the losing population must evolve to survive.

•   Evolution results in populations that occupy different niches, thereby reducing competition and promoting a more stable community.

Hunt or Be Hunted—Predation

When one organism eats another, we call that predation. The organism doing the eating is the predator, and the organism being eaten is the prey. Usually this results in the death of the prey (in the case of a hawk eating a mouse, for example), but it doesn’t have to (in the case of a giraffe eating the leaves from the top of a tree—the tree itself usually does not die).

Many times predation causes the prey to evolve. The prey evolves to better escape the predator. Plants evolve to have thorns, mice evolve to have brown fur for better camouflage, etc. In these cases, the evolution of the prey causes the predator to evolve—to better capture the prey. Herbivores evolve tougher mouth skin, hawks evolve to have better eyesight, etc. The alternate evolution of two species based on their interactions with each other is called coevolution.

Predators can affect the carrying capacity of an environment. In other words, an environment without predators will have a higher carrying capacity than an environment with predators. A marvelous example of this is the introduction of a species of perch into a lake in east Africa. The intent was to supply the locals living in that area with an additional source of income and food. At the time of introduction, the lake was filled with cichlids, a type of fish that feeds on plants, and fishing was abundant. The only problem (and it was a big one) was that the perch were natural predators of the cichlids. Because prior to this there were no predators, the cichlids had not evolved any defenses against them. The introduced perch completely destroyed the cichlid population, to the point that their own food supply was limited and their population decreased in numbers. In fact, the perch population declined so much that there were not enough perch (or cichlids, for that matter) to support the local fishing industry.

Quick Quiz #1

Fill in the blanks and check the appropriate boxes:

  1. The way an organism lives within its environment is called a

(A)  community

(B)  population

(C)  ecosystem

(D)  niche

(E)  species

  2. Groups of different species living together and interacting with the same environment is called a

(A)  community

(B)  population

(C)  ecosystem

(D)  niche

(E)  species

  3. Unrestricted population growth is called

(A)  carrying capacity

(B)  limited growth

(C)  exponential growth

(D)  ecosystem growth

(E)  community growth

  4. Members of the same community are also members of the same [  population  ecosystem ].

  5. Alternate evolution of two interacting species is called _________________________.

  6. Individuals [  can  cannot ] evolve.

  7. Hawks and wolves hunting the same population of rabbits is an example of [  competition  predation  both of these ].

Correct answers can be found in Chapter 15.


The various populations in a community can be classified based on where they get their food. We’ve already seen two such divisions—the autotrophs and the heterotrophs. Autotrophs, of course, are organisms that can make their own food, and heterotrophs are those that must eat other organisms. The groups of heterotrophs in a community can be further subdivided based on which other groups they eat. Sound complicated? Making you hungry? Check out the food chain:

1.   The food chain starts with organisms called primary producers. They’re photosynthetic—they take energy from the sun and convert it to carbohydrates. On land, the producers are plants. In water, they can be plants or algae.

2.   The next link in the food chain is made up of the primary consumers. These are organisms that eat the primary producers. Another word for primary consumer is herbivore—an animal that eats plants.

3.   The next link is made up of the secondary consumers. These are organisms that eat the primary consumers. Secondary consumers are carnivores—animals that eat other animals. They can also be herbivorous and eat plants. A word to describe an animal that eats both other animals AND plants is omnivore.

4.   The top of the food chain consists of the tertiary consumers. These are organisms that eat the secondary consumers. Tertiary consumers are carnivores that eat other carnivores.

Don’t Forget Decomposers

One way or another, all organisms die. When they do, their dead bodies are broken down (eaten, really) by other organisms called decomposers. Who are they? Bacteria and fungi who live off the dead remains of animals and plants. Bacteria and fungi are decomposers. Remember:

•   Producers (plants) use solar energy to convert carbon dioxide into sugars.

•   Primary consumers (herbivores) eat producers.

•   Secondary consumers (carnivores and omnivores) eat primary consumers (and producers).

•   Tertiary consumers (top carnivores) eat secondary consumers.

•   Decomposers eat the dead.

•   Animals, such as worms, catfish, and vultures, eat the waste and remains of dead organisms. These are known as scavengers.

There are more species and individuals at the bottom of the food chain than at the top. You can think of it as the pyramid on this page.

Think about a meadow. Grass and other plants grow in the meadow. Field mice live in the meadow and eat the grass. Insects are found in the meadow and they also eat plants. Sometimes they even eat other insects. Birds fly around eating seeds and insects. Snakes roam the meadow looking for mice. Hawks circle the meadow, pouncing on mice and sometimes snakes. What we’re trying to say here is that reality is a lot more complex than a simple food chain, so sometimes it’s referred to as a food web.

Here’s what it might look like. The arrows show who feeds whom.

The 10% Rule

There’s one last thing to remember about food pyramids, or food chains, or food webs, and that is that there’s more energy available at the bottom of the pyramid than at the top. In a food chain, only about 10 percent of the energy is transferred from one level to the next—this is called the 10% rule. The other 90 percent is used for things like respiration, digestion, running away from predators—in other words, it’s used to power the organism doing the eating! The producers have the most energy in the ecosystem; the primary consumers have less energy than the producers; the secondary consumers have less energy than the primary consumers; and tertiary consumers have even less, and decomposers have even less than that!

The energy flow, biomass, and numbers of members within an ecosystem can be represented in an ecological pyramid. Organisms that are “higher up” on the pyramid have less biomass and energy, and fewer numbers.

Quick Quiz #2

Fill in the blanks and check the appropriate boxes:

  1. Herbivores eat the [  primary consumers  primary producers ].

  2. Organisms that feed off dead and decaying material are called ______________________.

  3. Primary producers are [  autotrophs  heterotrophs ].

  4. There are more [  primary producers  primary consumers ].

  5. The least amount of energy is available at the [  bottom  top ] of the food chain.

  6. Organisms that eat both plants and animals are called ___________________________.

  7. Decomposers include both _______________________ and ________________________.

  8. An herbivore is a(n) [  autotroph  heterotroph ].

  9. In a food chain consisting of grass, grasshoppers, frogs, and bass, grasshoppers are [  more  less ] numerous than frogs, and frogs are [  more  less ] numerous than bass.

Correct answers can be found in Chapter 15.


We’ve been talking about biological communities and the way their inhabitants live together (and the way in which they eat one another). For the SAT Biology E/M Subject Test you should also know that communities of organisms undergo change over time—just like residential communities of people.

Think first about human beings and an uninhabited area outside a major city. Suppose that in, 1950 a few pioneers decide to build houses in the region and move in. Next, a couple of stores appear. More people become interested in the locality and they move in, too. The region develops slowly into a rural suburb. By 1960 it spawns some housing developments and a few little shopping strips. By 1965 roads widen, traffic increases, and several gas stations appear. The process continues—gradually. By 2000 the whole place is quite different from what it was in 1950. It boasts big shopping malls, wide roads, a lot of traffic, schools, businesses, apartment houses, and a lot of people. It starts to look like a city.

When that process of gradual change takes place in an ecological community, it’s called ecological succession. Think, for instance, about a rock with no living things on it. Often the first residents to move into the area are organisms called lichen. Lichen are the pioneers, and they are actually referred to as pioneer organisms because they’re the first to start living in a previously uninhabited area. When you think lichen, think pioneer organism.

As the lichen flourish, they give off substances that corrode the rock. The rock represents an altered environment, and it becomes attractive to other organisms like mosses and herbs. The mosses and herbs further affect the environment to make it suitable for shrubs and grasses. Trees move in next—first pine trees and then deciduous trees, like oaks, beeches, and maple. The rock—formerly lifeless—gave rise to an ecological community; it underwent succession, which begins, always, with some pioneer organism.

Let’s run through that succession again:

rock → lichen → mosses and herbs → grasses and shrubs → pine trees → deciduous trees

We said that the lichen in this succession is the pioneer organism. Does anyone else get a special label? The answer is yes. The deciduous trees—the oaks, beeches, and maples—are called the climax community. Once the succession has progressed as far as it can go, what you have left is the climax community. Unlike all of the plant communities that came before it (the lichen, the mosses and herbs, the grasses and shrubs, and the pine trees), the climax community is here to stay. In other words, the climax community is a stable community; it doesn’t change. Many things still happen within the climax community—plants and animals come and go, live and die, storms may hit it—but the essential nature of the climax community—that it’s made up of deciduous trees and has a characteristic fauna associated with it—stays the same.

Don’t Confuse Ecological Succession with Evolution

Ecological succession is NOT about evolution (a whole different ball game). Ecological succession has to do with continuous changes that take place within a community. There are predictable stages to it, as we just saw with our rock- lichen-grass-shrubs-trees example. Another big tip-off that you’re dealing with an ecological succession is the time frame involved: It’s a lot shorter than the time frame required for evolution to take place. When you think ecological succession, think predictable stages of plant communities usually over a period of decades. (In contrast, evolution takes place over hundreds of thousands or even millions of years.)

Quick Quiz #3

Fill in the blanks and check the appropriate boxes:

  1. When a plant community begins on a barren rock, the first organism to colonize the rock is most often [  lichen  moss ].

  2. In an ecological succession, each new plant community in an area [  coexists with  replaces ] the previous plant community.

  3. The final community in ecological succession is called the _________________________ community.

  4. Gradual, unpredictable change in plants that occurs over millions of years is called [  ecological succession  evolution ].

  5. The _________________________ organism is the one that first appears as the founder of a biological community.

  6. The final plant community in ecological succession is made up primarily of ___________________________________.

Correct answers can be found in Chapter 15.


Okay, we’ve talked about individual cells, individual organs, organ systems, organisms, groups of organisms (populations), and groups of populations (communities)—now we have to consider the community together with the environment it lives in. This is called an ecosystem.

We mentioned before that the environment contains both living (biotic) things and nonliving (abiotic) things. We’ve just talked about the living things (the organisms, populations, and communities); now let’s spend some time discussing a few of the nonliving things, such as water and chemical nutrients.

What Goes Around Comes Around—Nutrient Cycles

Because raw materials on Earth are limited resources, it makes sense to recycle them. Inorganic molecules are taken up by various organisms and converted into biologically useful forms; after these organic versions of the molecules cycle through the community, they are returned to their inorganic forms by decomposers. There are three cycles you should be familiar with: the water cycle, the carbon cycle, and the nitrogen cycle.

The Water Cycle

Water is obviously essential to living organisms—without it they die. Most of the water on the planet is NOT found in living organisms, however; it is found in the oceans. Because land-dwelling organisms need water, there must be a way to cycle the water from the oceans to the land and back. Here’s how it works.

The Water Cycle

Up, Up, and Away

Transpiration is water 
vapor escaping from the 
stomates of the leaves of 

Evaporation is water
escaping as vapor from a
body of water.

To sum up the water cycle, we can say that most water is taken up into clouds by evaporation and transpiration. The water returns to the oceans, land, and lakes by rainfall or other types of precipitation. Water that enters the soil returns to the oceans through runoff.

The Carbon Cycle

Carbon is the basic building block of all organic material. Most carbon is found as carbon dioxide in the atmosphere. Carbon is also used by plants to form organic molecules (sugars), which are then eaten by animals. The carbon is recycled to the atmosphere by respiration. Here’s the picture.

The Carbon Cycle

The Nitrogen Cycle

Nitrogen is an important nutrient for the production of protein—as you may recall, it’s found in all amino acids. Every organism—from bacteria to plants to fungi to animals—requires nitrogen for protein production. Even though most of the nitrogen on Earth is found as a gas in the atmosphere, this nitrogen is relatively unavailable for protein synthesis. Most nitrogen is taken up from the soil by plants in the form of nitrates (NO3) and incorporated into protein. These proteins are then consumed by animals, and the nitrogen is ultimately recycled to the soil when the animals die. In the soil, various types of bacteria convert the nitrogen into a usable form. Here’s how it works.

The Nitrogen Cycle

Basics of the Nitrogen Cycle

•   When animals and plants die, the nitrogen in their bodies is released into the soil.

•   The nitrogen in the soil is converted by bacteria into a usable form for plants. Some plants (legumes) have their own “resident” bacteria.

•   Some bacteria release nitrogen from the soil into the atmosphere; some take it out of the atmosphere and put it into the soil.

•   Plants use the nitrogen from the soil to produce protein.

•   Animals eat the plants and use the proteins to make their own proteins.

•   When animals and plants die, the cycle begins again.

Quick Quiz #4

Fill in the blanks and check the appropriate boxes:

  1. Most carbon is found

(A)  in the atmosphere

(B)  in plants

(C)  in fossil fuels

(D)  as carbon dioxide

(E)  as carbon monoxide

  2. Water and chemical nutrients are classified as [  biotic  abiotic ] elements of an ecosystem.

  3. Water moves from plants to clouds by

(A)  evaporation

(B)  condensation

(C)  precipitation

(D)  transpiration

(E)  decomposition

  4. Nitrogen is converted into usable forms in the soil by ____________.

  5. Carbon is returned to the atmosphere by [  photosynthesis  respiration ] and removed from the atmosphere by [  photosynthesis  respiration ].

  6. Nitrogen-fixing bacteria live in root nodules of __________________________________.

Correct answers can be found in Chapter 15.


Biomes are large areas classified mostly by the ecosystems—the climate and communities—they contain. Most biomes are terrestrial—found on land. Animal life is referred to as fauna, and plant life as flora. Some biomes are aquatic—found in water—and these biomes are the most stable because conditions such as temperature, oxygen, and light availability do not change too much over time.

All the biomes together make up the biosphere—the largest level of organization and, essentially, the planet Earth.

Terrestrial Biomes

Biome 1: The Tundra  A tundra is an area characterized by permafrost, permanently frozen topsoil. It’s found in the northernmost parts of North America, Europe, and Asia. Because the soil is frozen, deep root growth is difficult, so there are very few trees on the tundra. Most plants are short shrubs, grasses, lichen, and mosses. There are several different insects and a few mammals, such as reindeer, caribou, wolves, and bears.

Biome 2: The Taiga  Taiga is found a little bit south of the tundra. Another term for taiga is coniferous forest, because it contains many, many conifers (evergreen trees). Fauna includes many small mammals, such as squirrels and hares; larger herbivores, such as moose, elk, beavers, and deer; and larger carnivores, such as grizzly bears, wolves, and lynxes.

Biome 3: The Deciduous Forests  South of the taiga are the deciduous forests, where there’s a lot of rain and a wide variety of plants and animals. The climate has distinct hot and cold seasons. There are many more life forms in the deciduous forests than there are in the tundra or taiga. Examples of fauna are deer, skunk, beavers, raccoon, foxes, black bears, and squirrels. Examples of flora are maple trees, elm trees, oak trees, and chestnut trees. Deciduous trees are characterized by the fact that they drop leaves in the winter and the leaves regrow in the spring.

Biome 4: The Grasslands (Savanna)  Grasslands are characterized by low-growing plants and a few scattered trees. Tree growth is limited by regular periods of drought, grazing, and occasional fires. Tropical savanna (such as those in Africa) support some of the largest herbivores, including antelope, kangaroos, zebras, giraffes, and elephants. Temperate savanna (such as the prairies of North America) support wild horses, bison, and antelope; however, much of the original prairie lands have been converted to farmland because of their especially fertile soil. In both types of grasslands, insects are the dominant herbivores.

Biome 5: The Tropical Rain Forests  Tropical rain forests have the highest rainfall of any of the biomes and the greatest diversity in flora and fauna. Animal life includes insects, birds, monkeys, lizards, snakes, and tapirs. The trees grow very tall and many other plants grow around them, such as vines and smaller shrubs. The trees form a canopy above the rest of the vegetation, and sunlight barely reaches the lower regions.

Biome 6: The Desert  Deserts are the driest of all the biomes; they receive fewer than 30 centimeters of rainfall per year. Although we mostly associate deserts with hot temperatures, cold deserts also exist. The main thing to remember about deserts is their dryness. Animals and plants that live in deserts must be adapted to live in an arid environment. Desert plants are cacti and other succulents; desert animals are birds, small rodents, lizards, and snakes.

Aquatic Biomes

Aquatic biomes are divided into marine (saltwater) and freshwater biomes.

Biome 1: The Intertidal Zone (Marine)  This is the biome where land and water meet. The intertidal zone is subject to alternate periods of dryness and total submersion in water, as tides recede and come in. Organisms that live here include clams, snails, sea urchins, sea stars, crabs, barnacles, mussels, and sponges.

Biome 2: The Neritic Zone (Marine)  This biome extends from the intertidal zone, at the shore, to the edge of the continental shelf. Organisms here include kelp and other seaweeds, crustaceans, sea urchins, sea stars, and many species of fish. In warm waters, such as in the tropics, coral reefs are found in the neritic zone, supporting an immense variety of organisms.

Biome 3: The Oceanic Zone (Marine)  This biome is essentially open ocean. There is very little nutrient concentration here except for phytoplankton. There are many species of large, free-swimming animals that can search for food, such as fishes, sea turtles, large squids, and marine mammals. They often feed on one another. This biome can be further divided into pelagic (open water) and benthic (ocean bottom) zones. Also, the deepest parts of the ocean are known as abyssal zones.

Photic vs. Aphotic Zones

The photic zone extends 
from the surface of the 
water to the depth to 
which light will penetrate. 
Obviously, photosynthetic
organisms can thrive in 
this zone. Below the photic 
zone is the aphotic zone
where there is no light 
at all. Nutrients from the 
photic zone sink into this

Biome 4—The Littoral Zone (Freshwater)  This biome is found near the shore of a lake. Many plants grow here and support a wide variety of consumers, such as insects, snails, worms, amphibians, and some fish.

Biome 5—The Limnetic Zone (Freshwater)  This zone is farther from the shore and extends downward as far as light will penetrate. Again, because there is light available, many photosynthetic organisms and primary consumers thrive here.

Biome 6—The Profundal Zone (Freshwater)  This is essentially the aphotic region of the lake. Nutrients from the limnetic zone float down to support some primary consumers in this area. The primary consumers then become food for secondary consumers.


Unfortunately, humans have disturbed the existing ecological balance, and the results are far-reaching. Soils have been eroded and various forms of pollution have increased. The potential consequences on the environment are summarized below:

•   Greenhouse effect—The increasing atmospheric concentrations of carbon dioxide through the burning of fossil fuels and forests have contributed to the warming of the earth. Higher temperatures may cause the polar ice caps to melt and flooding to occur. Other potential effects of global warming include changes in precipitation patterns, changes in plant and animal populations, and detrimental changes in agriculture.

•   Ozone depletion—Pollution has also led to the depletion of the atmospheric ozone layer by such chemicals as chlorofluorocarbons (CFCs), which are used in aerosol cans. Ozone (O3) forms when radiation reacts with O2. Ozone protects the earth’s surface from excessive ultraviolet radiation. Its loss could have major genetic effects and could increase the incidence of cancer.

•   Acid rain—The burning of fossil fuels produces pollutants such as sulfur dioxide and nitrogen dioxide. When these compounds react with droplets of atmospheric water in clouds, they form sulfuric and nitric acids, respectively. The rain that falls from these clouds is weakly acid and is called acid rain. Acid rain lowers the pH of aquatic ecosystems and soil which damages water systems, plants, and soil.

•   Desertification—When land is overgrazed by animals, it turns grasslands into deserts and reduces the available habitats for organisms.

•   Deforestation—When forests are cleared (especially by the slash and burn method), erosion, floods, and changes in weather patterns can occur.

•   Pollution—Another environmental concern is the toxic chemicals in our environment. One example is DDT, a pesticide used to control insects. DDT was overused at one time and later found to damage plants and animals worldwide. DDT is particularly harmful because it resists chemical breakdown and today it can still be found in the tissues of nearly every living organism. The danger with toxins such as DDT is that as each tropic level consumes DDT, the substance becomes more concentrated by a process called biomagnification.

•   Reduction in biodiversity—As different habitats have been destroyed, many plants and animals have become extinct. Some of these plants could have provided us with medicines and products that may have been beneficial.

Quick Quiz #5

Fill in the blanks and check the appropriate boxes:

  1. The tropical rain forest has [  greater  lesser ] biological diversity than the tundra.

  2. The biome characterized by large numbers of evergreen conifers is the _________________.

  3. The primary plant forms of the [  taiga  tundra  desert ] are mosses, lichen, and wildflowers.

  4. The ocean floor is known as the _________________________ zone.

  5. Animals with adaptations for a dry environment would live in the [  savanna  desert ].

  6. The deepest zone of the ocean is the [  abyssal zone  pelagic zone ].

  7. Permanently frozen soil is a characteristic of ___________________.

  8. The biome with very fertile soil and many herbivores is the __________________________.

  9. Deer, bears, and raccoon are found in the [  tundra  rain forest  deciduous forest ], where as caribou and moose are found in the [  tundra  rain forest  deciduous forest].

10. Deciduous trees [  do  do not ] lose their leaves during cold seasons.

11. Phytoplankton would thrive well in the [  limnetic zone  profundal zone].

12. Succulent plants are well suited to [  savanna  desert ].

13. Areas of water where light does not penetrate are known as __________________________ zones.

14. The most northern biome is the [  taiga  tundra ].

15. The tundra [  does  does not ] grow many trees.

16. Coral reefs can typically be found in the [  intertidal zone  neritic zone].

Correct answers can be found in Chapter 15.

Key Words




exponential growth

limited growth

carrying capacity







food chain

primary producers

primary consumers


secondary consumers



tertiary consumers



ecological succession

pioneer organisms

climax community


the water cycle

the carbon cycle

the nitrogen cycle





terrestrial biomes



deciduous forests



tropical rain forests


aquatic biomes

marine biomes

freshwater biomes

intertidal zone

neritic zone

oceanic zone

pelagic zone

benthic zone

photic zones

aphotic zones

littoral zone

limnetic zone

profundal zone

greenhouse effect

ozone depletion

acid rain







•   Populations are groups of individuals that interbreed and share the same gene pool.

•   Populations can expand by exponential growth and by limited growth.

•   A community is a population that lives in a particular environment.

•   Food chains, food webs, and food pyramids show the movement of material and energy from one group of organisms to another.

•   Ecological succession is a change that a community will experience over time. It is not the same as evolution, however.

•   Three cycles—the water cycle, nitrogen cycle, and carbon cycle—move nutrients throughout ecosystems.

•   Biomes are the large areas classified by ecosystems.