Getting ready for the AP Biology exam? These 20 free practice questions cover key ideas from all eight units of the course, from the chemistry of life to ecology, each with a clear explanation. Try each question on your own first, then tap Show answer to check your thinking.
The questions are written in the style of the multiple-choice section of the exam. Many AP Biology questions describe an experiment or a situation and ask you to predict or explain what happens, so read each question carefully before you look at the choices.
What the AP Biology exam covers
- Chemistry of Life: water, pH and the structure of carbohydrates, lipids, proteins and nucleic acids
- Cell Structure and Function: organelles, membranes, osmosis and transport across the cell membrane
- Cellular Energetics: enzymes, cellular respiration and photosynthesis
- Cell Communication and Cell Cycle: signal transduction, feedback, mitosis and cell-cycle regulation
- Heredity: meiosis, Mendelian genetics and inheritance patterns such as sex linkage
- Gene Expression and Regulation: DNA replication, transcription, translation, gene regulation and mutations
- Natural Selection: evolution, Hardy-Weinberg equilibrium, phylogenetic trees and speciation
- Ecology: energy flow, population growth, community interactions and biodiversity
How to use these questions
Work through the questions without notes, the way you would on test day. Keep track of the ones you miss, and note which unit each one comes from. Two or three misses in the same unit is a sign to review that unit before moving on.
Read every explanation, even for questions you got right. AP Biology rewards understanding the mechanism, such as why an enzyme stops working or why an allele becomes more common, not just remembering a term.
Practice questions
Question 1
A researcher grows bacteria in a medium containing radioactive phosphorus (32P). After several generations, in which of the following molecules would the radioactive label most likely be found?
A. Glucose
B. Triglycerides (fats)
C. Nucleic acids such as DNA
D. Amino acids such as glycine
Show answer
Answer: C. Nucleic acids contain phosphate groups in their sugar-phosphate backbone, so they take up the radioactive phosphorus. Glucose and triglycerides are made only of carbon, hydrogen and oxygen, and amino acids contain carbon, hydrogen, oxygen and nitrogen (some also contain sulfur), but not phosphorus.
Question 2
A plant cell has a water potential of -0.6 MPa. It is placed in a sucrose solution with a water potential of -0.9 MPa. Which of the following best describes what happens?
A. Water moves into the cell, and the cell becomes more turgid
B. Water moves out of the cell, and the cell loses turgor pressure
C. Sucrose moves into the cell by osmosis
D. There is no net movement of water because both water potentials are negative
Show answer
Answer: B. Water always moves from higher water potential to lower water potential. Because -0.6 MPa is higher (less negative) than -0.9 MPa, water leaves the cell, and the cell loses turgor pressure. Osmosis is the movement of water, not of solutes like sucrose.
Question 3
Adding molecule X to an enzyme-catalyzed reaction lowers the reaction rate. When the substrate concentration is then greatly increased, the reaction rate returns to nearly its original maximum. Molecule X is most likely
A. a competitive inhibitor that binds to the active site
B. a noncompetitive inhibitor that binds to an allosteric site
C. a chemical that denatures the enzyme
D. a cofactor that the enzyme needs to function
Show answer
Answer: A. A competitive inhibitor competes with the substrate for the active site, so adding a lot more substrate can outcompete it and restore the maximum rate. A noncompetitive inhibitor changes the enzyme’s shape from another site, so extra substrate does not overcome it. A denatured enzyme would not recover at all.
Question 4
The chemical DNP makes the inner mitochondrial membrane leaky to hydrogen ions (H+). In cells treated with DNP, which of the following is most likely?
A. ATP production by ATP synthase decreases, while electrons continue to pass to oxygen
B. ATP production increases because hydrogen ions cross the membrane faster
C. Glycolysis stops immediately
D. Oxygen is no longer needed as the final electron acceptor
Show answer
Answer: A. ATP synthase makes ATP using the H+ gradient across the inner membrane. If H+ ions leak back across the membrane, the gradient is lost and less ATP is made. The electron transport chain can keep running and passing electrons to oxygen, so oxygen is still used. Glycolysis happens in the cytoplasm and does not depend on this gradient.
Question 5
The protein p53 stops the cell cycle at the G1 checkpoint when DNA is damaged, and it can trigger apoptosis if the damage cannot be repaired. A mutation that inactivates p53 would most likely cause
A. cells to stop dividing permanently
B. cells with damaged DNA to keep dividing, increasing the risk of cancer
C. DNA to be repaired more quickly
D. cells to skip the S phase of the cell cycle
Show answer
Answer: B. Without working p53, the checkpoint that stops cells with damaged DNA no longer works, and those cells are not removed by apoptosis. Damaged cells keep dividing and can build up more mutations, which is why p53 is called a tumor suppressor.
Question 6
A fruit fly heterozygous for two genes (AaBb) is crossed with a fly that is homozygous recessive for both (aabb). Of 1,000 offspring, 460 are AaBb, 450 are aabb, 45 are Aabb and 45 are aaBb. Which of the following best explains these results?
A. The two genes assort independently
B. The two genes are linked on the same chromosome, and the less common offspring result from crossing over
C. The two genes show incomplete dominance
D. New mutations occurred in most of the offspring
Show answer
Answer: B. If the genes were on different chromosomes, this test cross would give about 250 of each of the four types (a 1:1:1:1 ratio). Instead, most offspring look like the parents, which means the alleles are usually inherited together on the same chromosome. The 90 recombinant offspring come from crossing over, a recombination frequency of 9 percent.
Question 7
A segment of a DNA template strand reads 3′-TAC GGA TTC-5′. Which of the following is the mRNA sequence transcribed from this segment?
A. 5′-AUG CCU AAG-3′
B. 5′-ATG CCT AAG-3′
C. 5′-UAC GGA UUC-3′
D. 3′-AUG CCU AAG-5′
Show answer
Answer: A. mRNA is complementary and antiparallel to the template strand, and it uses uracil (U) in place of thymine (T). Pairing T with A, A with U, C with G and G with C gives 5′-AUG CCU AAG-3′. Choice B contains thymine, so it can’t be RNA, and choice D has the right bases running in the wrong direction.
Question 8
The lac operon in E. coli codes for enzymes that break down lactose. When lactose is absent, which of the following is true?
A. The repressor protein binds to the operator and blocks RNA polymerase, so the genes are not transcribed
B. Lactose binds to the operator and turns the genes on
C. RNA polymerase transcribes the genes at their maximum rate
D. The gene for the repressor protein is not transcribed
Show answer
Answer: A. The lac operon is inducible. With no lactose present, the active repressor binds to the operator and keeps RNA polymerase from transcribing the genes, so the cell does not waste energy making enzymes it doesn’t need. When lactose is present, a form of it binds to the repressor and releases it from the operator. The repressor gene itself is transcribed all the time.
Question 9
A patient takes an antibiotic for a bacterial infection. Most of the bacteria die, but a few survive and reproduce, and the new population is mostly resistant to the antibiotic. Which statement best explains this result?
A. The antibiotic caused resistance mutations in the bacteria that needed them
B. Resistant bacteria were already present because of random genetic variation, and they survived and reproduced more
C. Individual bacteria gradually got used to the antibiotic and became resistant
D. The antibiotic made all of the bacteria mutate at the same rate
Show answer
Answer: B. Natural selection acts on variation that already exists. A few bacteria happened to carry resistance alleles before the antibiotic was used. They survived and passed those alleles on, so the population changed. The common trap is thinking the antibiotic creates the mutations a bacterium needs; mutations are random, and individuals don’t evolve, populations do.
Question 10
Producers in an ecosystem capture 20,000 kcal of energy per square meter per year. If about 10 percent of the energy is passed from one trophic level to the next, about how much energy is available to secondary consumers?
A. 2,000 kcal
B. 200 kcal
C. 20 kcal
D. 18,000 kcal
Show answer
Answer: B. Primary consumers receive about 10 percent of 20,000 kcal, or 2,000 kcal. Secondary consumers receive about 10 percent of that, or 200 kcal. Choice A is the energy for primary consumers, which is a common mistake when students stop one level too early.
More practice from the AP+ workbook
These next 10 questions come straight from our AP+ Review Workbook, with the same explanations you’ll find in its answer key.
Question 11
A polypeptide chain contains 150 amino acids. How many peptide bonds are present?
A. 149
B. 150
C. 151
D. 75
Show answer
Answer: A. One peptide bond forms between each pair of neighboring amino acids, so a chain of n amino acids has n – 1 peptide bonds. A polypeptide of 150 amino acids has 149 peptide bonds.
Question 12
Which of the following provides the STRONGEST evidence that mitochondria evolved from ancient prokaryotes?
A. Mitochondria are found only in eukaryotic cells
B. Mitochondria produce ATP
C. Mitochondria have their own circular DNA and 70S ribosomes
D. Mitochondria are surrounded by two membranes
Show answer
Answer: C. Mitochondria have their own circular DNA and 70S ribosomes, just like free-living prokaryotes and unlike the 80S ribosomes the eukaryotic cell uses. This is strong evidence for endosymbiosis, the idea that mitochondria began as prokaryotes living inside a larger cell.
Question 13
A cell biologist measures glucose uptake as extracellular glucose concentration increases. Glucose moves down its concentration gradient, ATP depletion does not alter uptake, and the rate plateaus at high glucose concentration. This pattern is most consistent with
A. Simple diffusion, which has no upper limit on rate
B. Osmosis, which depends only on water potential differences
C. Active transport, which moves solutes without carrier proteins
D. Facilitated diffusion through a limited number of carriers
Show answer
Answer: D. The rate levels off even as glucose concentration keeps rising, which means the transport is saturable. That fits facilitated diffusion, which depends on a limited number of carrier or channel proteins. Because glucose moves down its gradient and uptake doesn’t depend on ATP, this is passive transport, not active transport.
Question 14
In the absence of oxygen, yeast produce ethanol and CO₂ through fermentation. The PRIMARY role of this process is to
A. Produce more ATP than aerobic respiration
B. Convert pyruvate into glucose
C. Build organic molecules from CO₂
D. Regenerate NAD⁺ to allow glycolysis to continue
Show answer
Answer: D. Fermentation regenerates NAD⁺ from NADH, so glycolysis can keep producing a small amount of ATP even without oxygen. It does not produce more ATP than aerobic respiration.
Question 15
In a signal transduction pathway, a kinase enzyme is activated and phosphorylates several downstream proteins, each of which phosphorylates further targets. This describes
A. A negative feedback loop that shuts off the kinase
B. Receptor-mediated endocytosis of the ligand
C. A point mutation in the kinase gene
D. Signal amplification by a kinase cascade
Show answer
Answer: D. Each activated kinase can phosphorylate many downstream targets, and each of those can act on more targets. This phosphorylation cascade amplifies a single signaling event into a much larger response in the cell.
Question 16
A woman who is a carrier for an X-linked recessive trait (XHXh) has children with a normal man (XHY). What fraction of their daughters will be carriers?
A. 0
B. 1/4
C. 1
D. 1/2
Show answer
Answer: D. Every daughter gets an XH from her father. From her carrier mother, she has an equal chance of getting XH or Xh. So daughters are XHXH or XHXh with equal probability, and 1/2 of the daughters are carriers.
Question 17
A researcher finds that genetically identical twins raised in different environments show different patterns of gene expression due to chemical modifications of DNA and histones, without changes to the underlying DNA sequence. This is BEST described as
A. An epigenetic change
B. A point mutation
C. A chromosomal inversion
D. Genetic recombination
Show answer
Answer: A. Epigenetic changes, such as DNA methylation or histone modification, change which genes are expressed without changing the DNA sequence itself. They can differ between genetically identical people because of differences in their environments.
Question 18
A small group of individuals colonizes a remote island. The allele frequencies of the island population differ significantly from the mainland. This BEST illustrates
A. Natural selection
B. The founder effect
C. Gene flow
D. Disruptive selection
Show answer
Answer: B. The founder effect happens when a small group starts a new population. The founders carry only a sample of the original population’s alleles, so by chance the new population’s allele frequencies can be quite different from the mainland’s.
Question 19
A population geneticist samples 500 individuals and finds 320 are homozygous dominant (AA), 160 are heterozygous (Aa), and 20 are homozygous recessive (aa) for a trait. What is the allele frequency of a in this population?
A. 0.04
B. 0.20
C. 0.16
D. 0.40
Show answer
Answer: B. Count the a alleles: each aa individual has two and each Aa individual has one, so there are (2 × 20) + 160 = 200 a alleles. The population has 2 × 500 = 1,000 alleles in all, so the frequency of a is 200/1,000 = 0.20. Choice A is the frequency of the aa genotype, not the a allele.
Question 20
A severe, unseasonal frost kills a large fraction of an insect population regardless of how dense the population was beforehand. This is an example of
A. A density-independent limiting factor
B. A density-dependent limiting factor
C. Competitive exclusion
D. Resource partitioning
Show answer
Answer: A. The frost kills insects no matter how crowded the population is, so its effect does not depend on population density. That makes it a density-independent limiting factor. Density-dependent factors, like competition for food, have a bigger effect as the population grows.
How did you do?
If you got 17 or more right, you have a strong foundation. Focus your review on the explanations for any you missed. If you got 12 to 16 right, you’re on track, but a few units need more practice. If you got 11 or fewer right, start with the unit reviews before doing more practice questions.
Our AP+ Biology Review Workbook covers every unit with clear concept reviews, data and graphing practice, lab and experimental design skills, free-response practice and two full-length practice exams with answers and explanations. It’s available as an instant PDF download or a paperback.
See the AP+ Biology Review Workbook →
Studying for more than one AP exam? Browse the full AP+ Exam Prep series.
Frequently asked questions
Are these questions like the real AP Biology exam?
They’re written in the style of the multiple-choice section and cover the same units and science skills. Official practice materials from the College Board are also worth using alongside them.
What’s the best way to study for AP Biology?
Review one unit at a time, practice reading graphs and data tables, and get comfortable explaining biological processes in your own words. Doing mixed practice questions regularly and reading every explanation, including for the ones you get right, builds the reasoning the exam rewards.
When is the AP Biology exam?
AP exams are given each May. Check the College Board’s AP website for the current exam schedule.
AP is a registered trademark of the College Board, which was not involved in the production of, and does not endorse, this page or our workbooks.