MCAT Biology Practice Questions

June 25, 2024

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Since biology is the foundation of medical science, it should come as no surprise that the majority of MCAT questions are related to biology. It is consequently essential to do well on the Biology and Biochemical Foundations of Living Systems section

Also, understanding how to answer questions about biology and related subfields during test preparation is a key component of attaining a solid MCAT score.

If you are looking for MCAT biology practice questions to assess where you are in your MCAT preparation, this is the article for you. Please get your pen and paper ready and let’s start!

What is MCAT Biology? 

The study of organisms' structure, growth, function, evolution, and distribution is the main focus of the scientific field of biology

It is a scientific study of how to examine life and living things. By using the scientific method, it establishes verifiable facts or develops ideas based on observations made during experiments on living organisms.  

Biology has a lot of subtopics but the MCAT only focuses on introductory biology. Introductory biology explores the fundamental ideas and principles of the study of living organisms and their interactions with the environment, as well as the overarching theories of life from biological research.

It shouldn't be a surprise that the MCAT covers biology extensively. It is only the CARS section that will not ask questions related to biology. 

Overall, 39 (out of 59) questions, or 65% in the MCAT Bio/Biochem portion, concern biology.
  • Introductory biology - 65%
  • First-semester biochemistry - 25%
  • General chemistry - 5%
  • Organic chemistry - 5%

Furthermore, three (out of 59) or 5% of the MCAT Chem/Phys questions are biology-focused.

The MCAT Psych/Soc has a similar ratio, with 5% of the questions being biological in nature.

Despite the fact that your biology review has a lot of content to cover, keep in mind that you do not need to be a biologist to master these MCAT parts. 

You should enroll in a variety of biology classes to make sure you are adequately prepared for the test.

Summary Table of Biology Distribution in the MCAT

MCAT Section

Biology Subject


Number of Questions 

(out of 59)

Biological and Biochemical Foundations of Living Systems

Introductory Biology



Chemical and Physical Foundations of Biological Systems

Introductory Biology



Psychological, Social, and Biological Foundations of Behavior

Introductory Biology



Total Number of MCAT Biology Questions: 45

Biology Topics to Study for the MCAT

Knowing which MCAT biology topics to study is crucial in your MCAT preparation. Biology is a broad subject and as stated earlier, you only have to focus on introductory biology. 

Here are the biology topics that are covered and included in the MCAT:

MCAT Biology Practice Questions

 No one would argue that answering practice questions before taking the actual MCAT helps test-takers a great deal. 

Practice questions help you get acquainted with how questions and options are structured. At the same time, they assess your level of readiness and help you improve on topics that you are weak at. 

Here are a few MCAT biology practice questions for you to answer.

1. Which of the analogies below between the blood pressure in a capillary in the neck and a capillary with an equivalent cross-sectional area in the right knee most closely follows Bernoulli's principle of fluid dynamics?

A. It is not possible to create a precise comparison without knowing the density and viscosity of the fluid.
B. Due to the rise in head pressure, the pressure in the neck is higher than the pressure in the knee.
C. Due to the rise in head pressure, the pressure in the knee is higher than the pressure in the neck.
D. Because of the equal dynamic pressure, the continuity equation states that the pressure in          the neck is equivalent to the pressure in the knee.

2. A woman is referred for genetic counseling when she has a maternal uncle (her mother's brother) and has two brothers who all have non-specific X-linked mental impairment. To determine if she is a carrier or not, there are no diagnostic tests available. Which of the following statements is TRUE?

A. She has a 25% chance of being a carrier, according to the odds.
B. There is a 50% chance that this woman's maternal grandmother carries the gene.
C. This means that the likelihood of her next son developing the condition or her next daughter developing the condition is one in five.
D. The woman already has two sons who are unaffected. Bayes' theorem can be used to determine that she is a carrier with a 1 in 5 probability. 

3. A possible novel oncoprotein connected to stomach cancer is being investigated by researchers. The mRNA transcripts for the new protein have been upregulated, according to the results of RT-qPCR. Which of the following could be a plausible mechanism for the protein's transcriptional upregulation?

A. Histone deacetylation
B. Chromatin structure opening
C. Increased production of ribosomes
D. Greater availability of amino acids

4. A patient with an asthma attack arrives at the emergency room. The patient's blood pH is 7.52 and they have been hyperventilating for the last hour. After receiving medication, the patient doesn't seem to improve, yet a subsequent blood pH check shows 7.41. Exactly why would this normal blood pH NOT be a comforting sign?

A. The pH reading of normal blood is probably off.
B. Respiratory failure could be setting in for the patient.
C. It's possible that the patient's kidneys made up for the alkalemia.
D. To counteract the alkalemia, the patient's blood should ideally briefly turn acidic.

5. Pink offspring are produced when a red bloom mates with a white flower. This is an illustration of:

A. Codominance
B. Heterodominance
C. Complete dominance
D. Incomplete dominance

6. Consider a mammalian species in which the alleles for black hair (B) , are dominant over the alleles for  brown hair (b) and straight hair (c). The phenotypic ratio is as follows when a genotype-unknown organism is crossed with a straight, brown-haired creature:

25% curly black hair
25% curly brown hair
25% straight black hair
25% straight brown hair

What genotype does the unidentified parent have?

B. bbCc
C. Bbcc
D. BbCc

7. A substance is administered to the cells in order to dissolve the proton gradient across the inner mitochondrial membrane. What is the overall outcome?

A. The spread of cancer is stopped
B. ATP synthase is unable to make ATP.
C. The cell will exocytose the dysfunctional mitochondria and discard them.
D. Cells will develop a new ATP production method quickly.

8. The pace of an enzyme-catalyzed reaction is quickly decreased by the addition of an unknown chemical. What kind of inhibition is most likely taking place if adding more substrate has no impact but adding an antibody for the unidentified molecule causes the reaction rate to return to normal?

A. Irreversible inhibition
B. Competitive inhibition
C. Uncompetitive inhibition
D. Noncompetitive inhibition

9. Prokaryotes lack membrane-bound organelles, in contrast to eukaryotes. Therefore, how do prokaryotes produce energy?

A. Energy is produced by photosynthesis in prokaryotes.
B. The specialized mitochondria were seen in prokaryotes.
C. Plasma membranes of prokaryotes produce proton gradients.
D. Sodium gradients are produced by prokaryotes across their nuclear membranes.

10. A brand-new drug has been developed that works wonders in the treatment of brain tumors, but it only lasts a short time within the body. Which method of delivery would offer the medication the longest chance to influence a brain tumor if it circulates in the bloodstream?

A. sublingual
B. inhalation
C. intravenous injection
D. subcutaneous injection

MCAT Biology Sample Passage 1

The stomach's parietal cells are essential for both food digestion and as a barrier against infections. Malnutrition and infections like sepsis caused by Clostridium difficile may occur when the parietal cells are not functioning properly. A balanced diet and sufficient nutrition are essential for maintaining a healthy digestive tract.

The hormone gastrin causes the stomach's parietal cells to release hydrochloric acid. When the stomach expands, the vagus nerve from the parasympathetic nervous system releases gastrin either directly or indirectly depending on whether proteins are present. Certain foods that have been consumed are broken down by hydrochloric acid, which also stimulates some zymogens to become activated and continue breaking down macromolecules. The majority of infections are also destroyed by the stomach's high acidity, which is caused by parietal cells releasing hydrochloric acid. Opportunistic pathogens may cause health issues when the parietal cell is not operating properly.

Additionally, parietal cells release intrinsic factor, a glycoprotein that binds to vitamin B12 to stop the vitamin from being destroyed by hydrochloric acid. The ileum of the small intestine absorbs the vitamin as it travels through the digestive system. Red blood cell formation requires vitamin B12 to function and. Aanemia may result from a diet low in vitamin B12.

The D cells in the stomach secrete somatostatin when the stomach's acidity is too high. The parietal cells' ability to release additional hydrochloric acid is suppressed by somatostatin.

11. What kind of criticism is this?

A. forward
B. neutral
C. positive
D. negative

MCAT Biology Sample Passage 2

The simplest functioning unit of life is the cell. Even though there are many distinct types of cells, they all share a few universal characteristics that define them as belonging to the category of "life." Everything that we regard to be living is made up of cells. The cell membrane is one of the most crucial components of a cell as it envelops a cell and isolates it from the outside world.

The cell membranes of creatures from the three main domains are comparable despite the fact that their surroundings are very varied. The cell is shielded by this phospholipid bilayer, which enables it to let some things in while blocking others. Although the fatty linkages in the membranes of creatures from various domains differ, they all fulfill the same crucial function.

The multitude of necessary proteins and signaling molecules found in membranes enable the inside of the cell to react to the outside of the cell. A multicellular eukaryote can employ this capability to enable cell communication. An extracellular signal may be used to alert other bacteria in a bacterial colony. The cell has control over its genetic makeup thanks to a network of molecular channels that transmit signals from the outside of the cell all the way inside to the nucleus and back out again. This enables rapid and efficient cellular responses, as well as cellular control over the duration of that condition. 

12. Which of the following is NOT a universal law of life?

A. DNA exists in cells.
B. The most basic building block of all life is the cell.
C. Every cell originates from an earlier cell.
D. A membrane surrounds the nucleus of every cell.

MCAT Biology Sample Passage 3

The rate-limiting enzyme in the phenylalanine metabolic pathway is phenylalanine hydroxylase. The addition of a hydroxyl group to the aromatic ring of phenylalanine is catalyzed by phenylalanine hydroxylase, turning it into tyrosine. Tetrahydrobiopterin (BH4) and iron are the two cofactors needed for the proper function of this enzyme (Figure 1). When the cofactor tetrahydrobiopterin is lacking, another type of PKU may develop.

Pheoh Hydroxylates Tetrahydrobiopterin While Converting Phenylalanine Into Tyrosine.

Source: Wikipedia

The hereditary condition known as phenylketonuria (PKU) is caused by an inactivating mutation in the gene encoding the phenylalanine hydroxylase enzyme. Due to this mutation, people with PKU are unable to metabolize phenylalanine and turn it into tyrosine, causing phenylalanine to accumulate in their bodies. Excess phenylalanine is then metabolized to form phenylpyruvate via the action of the enzyme phenylalanine transaminase. Phenylalanine can accumulate to harmful levels if enzymes aren't present to break it down, especially when eating foods high in protein like cheese, milk, nuts, and meat.

If PKU is not treated, it can result in severe health issues such as brain damage, behavioral issues, and seizures. A low-protein diet supplemented with a formula combining amino acids and other necessary elements is one of the treatments. More than 300300300 mutations that cause PKU have been found, the majority of which are in the catalytic domain of phenylalanine hydroxylase.

13. What impact, if any, might the PKU-related mutation have on the catalytic effectiveness of phenylalanine transaminase?

A. Kcat will rise while Km will fall, increasing the catalytic efficiency.
B. Kcat and Km won't alter, maintaining the same catalytic efficiency.
C. Km will rise while Kcat declines, resulting in a decline in catalytic efficiency.
D. The drop in Kcat and Km will have an undetermined impact on the enzyme's catalytic effectiveness.

14. How would one calculate the kinetics of phenylalanine hydroxylase using the Michaelis-Menten equation given a deficit in tetrahydrobiopterin?

A. The Kcat value would take the substrate's effects into account.
B. Since cofactors are also substrates, cofactor concentration could be described by the same term as substrate concentration.
C. Since the cofactor concentration is not represented by a term in the Michaelis-Menten equation, no adjustments are necessary.
D. The Michaelis-Menten equation could not be employed in this situation as it stands since this reaction would have non-Michaelis-Menten kinetics.

15. What impact might the PKU-related mutation have on the pace at which phenylalanine transaminase catalyzes the reaction?

A. Due to the disease-related mutation, the response rate will drop.
B. Due to the stability of Km and Vmax, the reaction rate will not fluctuate.
C. As the concentration of phenylalanine rises, the reaction rate will as well.
D. Due to an increase in phenylalanine concentration, the reaction rate will slow down.

16. People who are heterozygous for the PKU mutation exhibit very small elevations in phenylalanine levels. How might the phenylalanine hydroxylase reaction rate of a person heterozygous for the PKU mutation differ from that of a person without any genes that have been altered?

A. A reduction in the reaction's Km would cause the reaction rate to rise.
B. An increase in the reaction's Km would result in a drop in reaction rate.
C. A reduction in the reaction's Vmax would cause the reaction rate to decrease.
D. An increase in the reaction's Vmax would result in an increase in the reaction rate.

MCAT Biology Sample Passage 4

When their three-month-long protest against the construction of a highway through Moscow's Khimki forest was ignored this morning, Russian environmentalists broke down in tears.

The lone forest in Moscow will be directly traversed by this new highway, whose construction was recently approved. To make room for the project, over 101010 square kilometers of forest will need to be clear-cut.

Artur Savrasov, a 24-year-old graduate of Moscow University, stated, "It's like taking a knife to your own face to try and seem nicer."

Viktor Bogdanov, the protest's organizer, stated, "I don't think the administration is aware of the impact this decision would have on Moscow and will leave [to] our descendants."

Since most of the food sources in the Khimki forest are confined to certain locations that can only be obtained on one side of the proposed roadway, many kinds of animals will no longer have enough access to food.

It's probable that allopatric speciation will take place as a result of the construction of this route. When a physical barrier separating two groups of animals from the same species is introduced, the process known as allopatric speciation causes the animals to diverge into new species.

While this would allow for a more varied population of animals in the forest, many environmentalists think that the populations on either side of the highway will shrink too much, which might cause the extinction of a lot of the native animals to the Khimki forest, including the snowy owl.

According to reports, construction will start in early 2024.

17. By the highway, two populations of snowy owls are split apart. Which prezygotic reproductive isolation prohibits mating between the two populations?

A. Habitat Isolation
B. Artificial Isolation
C. Gametic Isolation
D. Temporal Isolation

18. How do you anticipate the size of the several gene pools to alter when the local snowy owl population is split into two smaller populations by the highway?

A. As the local population grows, so will the gene pool.
B. As the local populations decline, the gene pool will expand.
C. As the local populations grow, the gene pool will also shrink.
D. As the local populations decline, the gene pool will also decrease.

19. Peripatric speciation happens when a tiny group of species enters a novel, isolated niche. It is analogous to allopatric speciation. Which of the subsequent occurrences might lead to peripheral speciation?

A. A herd of mountain goats moves to a new mountain where they can find more of their kind.
B. A colony of turtles is split between two sides of an island after an earthquake splits it in two.
C. After a forest is cleared, a population of poison dart frogs is left behind, separated by huge fields of crops.
D. A school of fish gets imprisoned in a cargo ship's water tanks and later released in a different ocean.

20. One of the trees being felled to make room for the highway is home to a colony of Tangarana Ants. Over 99 %99%99 of the ant population is wiped out when the ants are forced to travel underground, where they are exposed to a very different living environment.

This is an illustration of:

A. Habitat Isolation, because the ants can't get to their natural habitat.
B. The Bottleneck Effect, because only a small number of ants were able to withstand the habitat change.
C. Extermination after a severe environmental stress, because the ants cannot survive outside of their natural home.
D. Interbreeding due to the ants being compelled to reproduce with a smaller portion of the larger initial population of ants.

Answer Key:

Mcat Biology Practice Question Answer Key

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