CLEP / Biology

Free Practice Test: CLEP Biology

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  • REA CLEP Biology

REA CLEP Biology

*At the time of publishing.


Getting ready for the Biology CLEP exam? Excellent! Here’s a quick look to help you out. The exam has about 115 questions designed to cover a freshman single-semester course.

When you think about Biology, what comes to mind first? Plants and animals? Well, organisms are going to be about a third of the test. Any creature is fair game, but there will be an emphasis on vertebrate animals and flowering plants (phew!). Another third will be smaller stuff – cells and the chemistry of life. That leaves the larger-scale material to round out the set. Populations, evolution, and behavior emerge from groups of organisms, so these sorts of questions make up the final third of the exam.

Fast Biology Study Guide

There’s an awful lot of information covered by the exam. Possibly you’ve already learned a lot of the material in high school, but you’ll want to be reasonably thorough on the review because not only is “life” a pretty broad study topic, there’s a fair bit of detail expected.

The exam covers three main categories:


Unless you’re already great at Chemistry, this section might be the toughest. To understand how a living thing works, at some point you need to take a look at its tiniest parts: the molecules it’s built from. You’ll want to know some of the basics of chemistry, especially the chemistry of biological polymers—the carbohydrates, lipids, proteins, and good old DNA and RNA that all living things are made from—as well as the chemistry of water, because all life we know of depends on water. (That’s why scientists were so excited to find water on Mars!)

Then put these together to make cells, and learn a little about those. Know the differences between primitive prokaryotes (including all bacteria) and more complex eukaryotes. A hint for remembering the functions of the organelles of a eukaryotic cell: think of each as a function within a city. Most people remember the mitochondria are the powerhouses of the cell, but did you realize the Golgi bodies are like UPS stores? Prokaryotes don’t have organelles, just loops of DNA with ribosomes to make proteins, so no worries there.

Expect this section to include molecular genetics, mitosis, and meiosis. If you can’t keep the last two straight, remember mitosis can happen in your toes-es. (Sorry!) Meiosis divvies up your chromosomes for the next generation, so it’s only going to happen in gonads. This section is already stuffed full of stuff to remember, but pack in everything to do with enzymes and energy for life, including respiration and photosynthesis. Then take a deep breath and realize it’s only a third of the exam, so most of the questions will be about things big enough to see.


Now it’s time to look at the whole organism. The basic pattern is to cover structure, function, hormones, reproduction and development, and responses to the environment in some detail. Don’t make the mistake of forgetting about plants! Most of the plant questions will be about flowering plants, or angiosperms.

You’ll want to know about their main parts: root, stem, and leaves, as well as their reproductive parts: flowers, fruits, and seeds for angiosperms. Don’t forget to do a little review of more primitive plants because they’ll throw in a few of those. No plants except angiosperms will have flowers or fruits, but most will have seeds and those that don’t will have spores. Review how each of these plant parts functions. How does that water make it to the top of the tree? How does the tree feed each of its cells?

There may be a little more about plant reproduction than you’d guess, including keeping track of reproductive cells and what parts are haploid (one set of chromosomes) diploid (two sets, with each chromosome having a partner), or even triploid during the plants’ life cycles. How do plants use day and night length to know when to flower (photoperiodism)? Delve into the plant hormones as well as ways in which plants grow in response to stimuli (tropisms). For example, plants display gravitropism when shoots sense gravity and grow upwards.

On to animals! Similar to the way you did for plants, you’ll want to cover all the major body systems (nervous, circulatory, etc.) and main hormones. Animals control their internal environment pretty strictly through a number of processes (homeostasis). Your body temperature stays pretty close to 98.6 degrees Fahrenheit, for example. Beyond structure and function in animals, have a look at embryonic development, Mendelian genetics, chromosomal genetics, and the different ways in which traits determine inheritance (single-gene traits, sex-linked traits, polygenic traits, etc.) to round out your study of organisms.


This section is about everything above the scale of the single organism. Here we’re talking about populations, communities, ecosystems, and biomes. Let’s walk you through that. Populations are groups of a single type of organism that (at least potentially) could interbreed.

For example, let’s say we have a Ponderosa Pine population in the foothills of a local mountain. When you consider all the populations of different species in one area, you have a community. If you go into the Ponderosa Pine forest, you could easily see blue grama grass and Abert’s squirrels because they belong to the same community. When you add in the non-living environment—the soils, rocks, and streams—that’s the ecosystem.

Biomes are pretty cool because they show how certain environments lead to certain life forms no matter where they are. You can compare a deciduous forest in eastern North America to one in northeast Asia, and they’ll look pretty similar at a glance even if there’s not a single species in common between the two. They are both deciduous forest biome.

So now the stage is set, cue the action. Energy and various nutrients cycle through the ecosystem, and you’ll want to know how this occurs for each. Populations grow and stabilize or shrink over time affected by factors such as birth, death, competition, predation, and migration. When organisms alter their own environment to make it less suitable for themselves, they are replaced by other species in a process called succession, ending with a climax community that can sustain itself until something disturbs the environment, such as a fire.

Species adapted to these climax communities tend to be “K” selected and good at competition, while the species that rush in to take advantage of disturbances are “r” selected and good at reproducing fast. Now zoom out and look at what’s happening over evolutionary time. Sometimes potentially competing organisms can coexist by developing separate niches to avoid eating each other’s lunch. For example, two species of birds might evolve different beak sizes to eat larger and smaller seeds, allowing them to both make a living in the same community.

When a few founding organisms make it to an isolated area, niche differentiation can lead many new species to evolve in a process called adaptive radiation. Darwin came up with his theory of evolution by natural selection based on the species he found on the Galapagos Islands, where adaptive radiation had occurred. The history of evolutionary theory, the mechanisms of natural selection and evolution, and the different types of evidence we have for evolution are all fair game, as is the evolutionary history of humans and other species.

Humans are real game-changers in the process of evolution. Social biology includes a look at how human populations grow and how we are affecting other organisms and our environment (pollution, genetic engineering, habitat destruction, etc.) and ourselves (modern medicine).

Special Note

Science is a process, and you will be expected to understand something about how to design experiments, collect data, and interpret experimental evidence. This will be incorporated into the topics of the exam already described.

You may be given some experimental evidence to interpret or be asked about how information is collected or hypotheses are made, or even about the social consequences of scientific endeavors. So be sure you understand something about the scientific method and experimental design, as well as human impacts on the biosphere.

Biology Free Practice Test

So, are you ready to test the waters? Take this practice quiz and judge your preparation level before diving into deeper study. All test questions are in a multiple-choice format, with one correct answer and four incorrect options. The following are samples of the types of questions that may appear on the exam.
Question 1: In the graph in context, the Y axis represents enzyme activity. Based on the graph, which is the optimum temperature for the peroxidase enzyme?

  1. 25 degrees C
  2. 100 degrees C
  3. 40 degrees C
  4. 32 degrees C

context image for this question

Correct Answer: D. 32 degrees C

Explanation: The highest enzyme activity is seen around this temperature. It's likely that the enzyme operates at around this temperature in whatever organism it was extracted from. At 100 °C, the enzyme doesn't seem to be working at all. Probably it was denatured and inactivated by the heat.

Question 2: To produce the graph in context, students recorded the enzyme activity at several pre-determined temperatures. In the laboratory exercise, which was the role of temperature?

  1. A dependent variable
  2. An independent variable
  3. An uncontrolled variable
  4. The control

context image for this question

Correct Answer: B. An independent variable

Explanation: Independent variables are controlled or determined by the experimenter, in order to figure out what their effects on the dependent variable might be. The dependent variable is what's being affected by the experimental treatments. It's recorded during the course of the experiment. Enzyme activity was the dependent variable in this experiment. The control is an experimental treatment used for comparison. A test tube without any enzyme in it might serve as the control. You really don't want to have any uncontrolled variables in your experiment, because they'll cause experimental error. If a student accidentally put more enzyme in one test tube than in another, that would make “enzyme concentration” an uncontrolled variable and mess up the results.

Question 3: Runoff from a farm washes fertilizer into a pond, resulting in increased algal growth, reduced oxygen, and eventually death of the fish. This sequence of events is best described as which process?

  1. Primary succession
  2. Denitrification
  3. Autotrophy
  4. Eutrophication

Correct Answer: D. Eutrophication

Explanation: Eutrophication can happen naturally but is often accelerated and more severe due to human activities. Eutrophic lakes can sometimes disappear entirely, becoming filled in by the sediments from dead organisms and bacteria.

Question 4: Bats, whales, dogs, and humans all have a long bone in their front limbs attached to two parallel bones at a joint. Anatomical structures such as these are said to be

  1. Analogous
  2. Homologous
  3. Vestigial
  4. Fulfilling the same function

Correct Answer: B. Homologous

Explanation: Homologous structures are thought to be evidence of evolution because the same basic body plan appears to have been adapted over time to perform different functions. Vestigial structures are homologous structures that have lost their use, such as the tiny vestigial tailbone in humans. Analogous structures perform the same functions, but aren't actually related. The wing of a butterfly and the wing of the bird are examples of analogous structures.

Question 5: Why is a single nucleotide substitution of uracil for thymine in the coding region of a DNA strand likely to have little effect on the organism?

  1. I only
  2. III only
  3. I and IV
  4. II and IV

I. Both uracil and thymine nucleotides will pair with adenosine
II. The genetic code is redundant
III. Single nucleotide substitutions rarely have much effect
IV. The substitution is likely to be detected and repaired because DNA does not ordinarily contain uracil.

Correct Answer: C. I and IV

Explanation: DNA contains four different nucleotide bases: adenine, thymine, guanine, and cytosine, or A, T, G, C. Adenine pairs with thymine, and guanine pairs with cytosine. Uracil is a nucleotide ordinarily found only in RNA, where it takes the place of thymine and, like thymine, pairs with adenosine. So, “I” is correct: both the original and the mutated DNA will function to produce the same messenger RNA—but is it the best ? The genetic code IS redundant (II), meaning that there is more than one way to code for many of the amino acids in the proteins that will be constructed according to the DNA's code, but this has nothing to do with this particular mutation. Single nucleotide substitutions CAN have quite a large effect, so “III” is incorrect. (Try having sickle cell anemia, for example!) But what about “IV,” the substitution will be repaired? It probably will be fixed, because as mentioned earlier, DNA doesn't have uracil, and there are mechanisms in place to remove and replace uracil when detected. So the best is “c,” I and IV. Probably the substitution will be repaired, but if it isn't, it's not going to change the messenger RNA that the DNA produces.

Question 6: When glucose molecules are metabolized in an aerobic cell, the energy is used to produce ATP in a series of biochemical steps. Place these events in the correct sequence

  1. IV, I, III, II, V
  2. II, III, I, V, IV
  3. IV, III, I, II, V
  4. II, I, III, IV, V

I. Pyruvate is converted to Acetyl Coenzyme A
II. In the mitochondrion, electron carriers donate electrons to the electron transport chain to produce a proton gradient.
III. A molecule enters the citric acid cycle, or Krebs cycle, leading to the production of 3 NADH, 1 FADH2, and 1 ATP
IV. During glycolysis, a molecule is cleaved into two parts, producing 2 NADH and 2 ATP molecules
V. ATP synthase admits protons into the interior matrix of the mitochondrion, producing up to 34 ATP.

Correct Answer: A. IV, I, III, II, V

Explanation: During glycolysis, a glucose molecule is split in two (IV), producing two molecules of pyruvate. The pyruvate is converted to Acetyl Coenzyme A (I), which enters the citric acid cycle in the mitochondrion, where electron carriers NADH and FADH2 are produced (III). These electron carriers donate their electrons to the electron transport chain to produce a proton, or H+, gradient across the inner membrane of the mitochondrion (II). ATP synthase lets these protons back into the inner chamber of the mitochondrion, producing ATP (V). This is glycolysis and cellular respiration in a nutshell. If you've forgotten them, you'll need to buck up and study, but try to keep track of this “nutshell” view as a framework, so you don't get lost. (And if you haven't forgotten them, we're really impressed!)

Question 7: Which is the product of anaerobic respiration in humans?

  1. Humans can't perform anaerobic respiration.
  2. Carbon dioxide only
  3. Lactic acid
  4. Carbon dioxide and ethanol

Correct Answer: C. Lactic acid

Explanation: When humans perform vigorous exercise, such as sprinting, the muscles may require more oxygen than the lungs and circulatory system can immediately supply. Usually, glucose is broken down into carbon dioxide and water, but this process of aerobic respiration requires oxygen. If the oxygen is lacking, the glucose will be converted into lactic acid temporarily. Oxygen will still be needed later to break down the lactic acid. That's why a sprinter may be gasping for air for a while after reaching the finish line. They're making up their “oxygen debt.” If only student loans were that easy to pay off!

Question 8: Which cellular organelles are likely to be more prevalent in a cell that produces steroid hormones?

  1. Rough endoplasmic reticulum
  2. Mitochondria
  3. Smooth endoplasmic reticulum
  4. Lysosomes

Correct Answer: C. Smooth endoplasmic reticulum

Explanation: Smooth ER produces cellular products such as lipids and steroids. Rough ER makes proteins. Mitochondria produce ATP for energy, and lysosomes break down and recycle waste materials.

Question 9: Human babies with a low birth weight and those with a high birth weight are less likely to survive than those with an average birth weight. This is an example which process?

  1. Punctuated equilibrium
  2. Disruptive selection
  3. Directional selection
  4. Stabilizing selection

Correct Answer: D. Stabilizing selection

Explanation: Stabilizing selection favors intermediate traits and tends to cause traits to cluster more tightly around an optimum value. Directional selection causes traits to become more extreme in a favored direction. For example, if the fastest cheetah gets more prey and so is more likely to survive, then there is selective pressure for cheetahs to get faster and faster. Disruptive, or diversifying, selection favors a lot of variation. The human immune system is under disruptive selection, because the more variation we have in our receptors to recognize invading pathogens, the better.

Question 10: How is the endosperm of a flowering plant's seeds produced?

  1. The zygote splits in two. One of these cells produces the embryo, and the other makes the endosperm.
  2. The endosperm is produced entirely by the maternal cells, without the need for fertilization.
  3. Two sperm travel down the pollen tube to the embryo sa One fertilizes the egg, and the other fertilizes a polar nucleus to produce diploid endosperm.
  4. Two sperm travel down the pollen tube to the embryo sa One fertilizes the egg, and the other fertilizes the two polar nuclei to produce triploid endosperm.

Correct Answer: D. Two sperm travel down the pollen tube to the embryo sa One fertilizes the egg, and the other fertilizes the two polar nuclei to produce triploid endosperm.

Explanation: Two sperm travel down the pollen tube to the embryo sac. One fertilizes the egg, and the other fertilizes the two polar nuclei to produce triploid endosperm.; This kind of “double fertilization” is a defining characteristic of flowering plants.

More CLEP Biology Study Resources

Looking for a study guide to fill a couple gaps, or just want a full length practice exam? You can find a few of my favorite resources below. Note that some of the links are affiliate – meaning I’ll make a few dollars if you purchase, but I’m only sharing those resources that were genuinely helpful during my own CLEP journey.
Official CLEP Study Guide

While quite short on the study side of things, the official CLEP book is the go-to final practice test. Since this is the only official practice test available, I normally use it as my final spot check before taking the test.

REA CLEP Biology

REA offers a great combination of study guide and practice questions. This book functions well as the central pillar of a strong CLEP prep strategy, with resources like the Official CLEP Study Guide (above) providing a great final practice test at the end.

InstantCert Academy

The website looks like it was made before the internet, but it’s legitimately the single most useful study guide I’ve found yet. Basically it’s a series of flashcards that help you study in a fast paced and fun way.

Plenty of other resources exist – just do a quick internet search – but these are the three that I’ve personally found the most helpful back when I did CLEP.