Biology is the section that decides most MDCAT results. It carries 81 of the 180 marks — 45% of the paper, more than Chemistry and Physics combined. A student who is strong in Biology and average elsewhere usually outscores a student with the reverse profile, simply because there is more of it to get right.
The PMDC 2026 curriculum organises MDCAT Biology into 16 units, and they are not weighted evenly. Cell Structure & Function, Bioenergetics, Coordination & Control, Reproduction and Evolution reliably produce more questions than smaller units like Acellular Life or Biotechnology. That does not make the small units safe to skip — a single unfamiliar question on viral structure costs the same mark as a question on photosynthesis — but it should shape how you divide your time.
Most MDCAT Biology questions are recall: a definition, a structure, a pathway, a number. Roughly a third are application — you are given a scenario and asked what follows. The questions below mix both, because practising only recall leaves you unprepared for the ones that actually separate candidates.
Every question on this page shows the correct answer and an explanation of why it is correct. Read the explanations even for questions you answered correctly; the reasoning is often more useful than the answer, and the MDCAT repeats concepts far more reliably than it repeats questions.
40 free Biology MCQs with answers
Work through a chapter's questions in one sitting rather than grazing across subjects. When you get one wrong, go to the relevant notes page before moving on — reading the explanation alone tends to produce recognition rather than understanding.
Acellular Life
Q1. HIV primarily attacks which type of immune cells?
Answer: B — HIV specifically targets and destroys CD4+ helper T-lymphocytes weakening the immune system.
AIDS and HIV Infection
Q2. Which of the following is NOT a criterion for classifying viruses?
Answer: B — Viruses are acellular and do not have their own mode of nutrition so this is not a classification criterion.
Viruses
Bioenergetics
Q3. How many ATP molecules are produced from the complete oxidation of one glucose molecule?
Answer: C — Complete aerobic oxidation of one glucose molecule yields approximately 38 ATP molecules.
Respiration
Biological Molecules
Q4. Water is an excellent solvent because of its:
Answer: A — Water's polar nature allows it to dissolve many ionic and polar substances effectively.
Biological Importance of Water
Q5. Which of the following elements is found in all organic biological molecules?
Answer: B — Carbon is the fundamental element of all organic molecules due to its ability to form four covalent bonds, creating diverse molecular structures including chains, rings, and branched configurations.
Biological molecules
Q6. Glucose is a:
Answer: D — Glucose is a monosaccharide (simple sugar) with the formula C6H12O6.
Carbohydrates
Q7. Glycoproteins are examples of:
Answer: A — Glycoproteins are conjugated molecules consisting of a protein covalently bonded to carbohydrate groups.
Conjugated molecules
Q8. Triglycerides are composed of:
Answer: D — A triglyceride consists of one glycerol molecule esterified with three fatty acid chains.
Lipids
Q9. How many amino acids are commonly found in proteins?
Answer: B — There are 20 standard amino acids that are commonly found in proteins.
Proteins
Q10. RNA differs from DNA in having:
Answer: B — RNA contains uracil instead of thymine and has ribose sugar instead of deoxyribose.
Ribonucleic acid (RNA)
Q11. The DNA double helix model was proposed by:
Answer: C — James Watson and Francis Crick proposed the double helix model of DNA in 1953.
Structure of DNA
Biotechnology
Q12. Recombinant DNA technology involves:
Answer: A — Recombinant DNA technology uses restriction endonucleases to cut DNA and ligases to join fragments from different sources, creating novel DNA combinations for biotechnological applications.
Biotechnology and Health Care
Cell Structure & Function
Q13. Which organelle is present in plant cells but absent in animal cells?
Answer: B — Plant cells have a rigid cell wall made of cellulose which is absent in animal cells.
Cell structure
Q14. Chromosomes are composed of:
Answer: B — Chromosomes consist of DNA wrapped around histone proteins forming chromatin.
Chromosomes
Q15. The rough endoplasmic reticulum is studded with:
Answer: C — Rough ER has ribosomes attached to its surface giving it a rough appearance and enabling protein synthesis.
Cytoplasmic Organelles
Q16. Prokaryotic cells lack:
Answer: B — Prokaryotic cells do not have a membrane-bound nucleus; their DNA is in the nucleoid region.
Prokaryotic and Eukaryotic cell
Circulation
Q17. Arteries differ from veins in that arteries:
Answer: D — Arteries must withstand and maintain high pressure; their walls are thicker with abundant elastic and smooth muscle layers (tunica media) compared to veins.
Blood Vessels
Q18. During ventricular systole, the atrioventricular (mitral and tricuspid) valves are:
Answer: A — During ventricular contraction (systole), the AV valves close (producing the first heart sound, S1), preventing blood from flowing back into the atria.
Cardiac Cycle and Phases of Heartbeat
Q19. The left ventricle has a thicker muscular wall than the right ventricle because it:
Answer: D — The left ventricle pumps blood into the systemic circulation (aorta) against much higher peripheral resistance, requiring a thicker, more muscular wall.
Human Heart
Q20. Lacteals in the intestinal villi are lymphatic capillaries responsible for absorbing:
Answer: B — Lacteals absorb chylomicrons (dietary fat particles) and fat-soluble vitamins from the intestinal epithelium; absorbed lipids enter the lymphatic system as chyle.
Lymphatic System
Q21. Lymph coming from the right side of the head, the right arm and the right half of the thorax is drained by the:
Answer: A — The right lymphatic duct collects lymph from the right upper quadrant of the body and empties it into the right subclavian vein; the rest of the body is drained by the thoracic duct.
Lymphatic system
Coordination & Control / Nervous & Chemical Coordination
Q22. The resting membrane potential of a neuron is approximately:
Answer: C — The resting membrane potential of a typical neuron is approximately -70 mV (inside negative).
Nerve Impulse
Q23. The basic structural and functional unit of the nervous system is:
Answer: B — The neuron (nerve cell) is the basic structural and functional unit of the nervous system.
Neurons
Q24. The largest part of the human brain is:
Answer: B — The cerebrum is the largest part of the brain responsible for higher functions like thinking and voluntary actions.
Parts of Brain
Q25. A sensory receptor is best described as a biological:
Answer: A — A receptor detects a stimulus and converts its energy into the electrical energy of a nerve impulse; this energy conversion is exactly what defines a transducer.
Receptors
Digestion
Q26. Chemical digestion of carbohydrates begins in the:
Answer: D — Salivary amylase (ptyalin) secreted by salivary glands begins the hydrolysis of starch to maltose in the oral cavity.
Human Digestive System
Q27. The complete set of permanent teeth in an adult human being consists of:
Answer: C — The adult dentition has eight teeth in each half jaw, two incisors, one canine, two premolars and three molars; this gives a total of thirty-two teeth.
Human digestive system
Enzymes
Q28. A competitive inhibitor is able to occupy the active site because it:
Answer: D — A competitive inhibitor is structurally similar to the normal substrate; so it fits the active site and blocks it without being converted into product.
Enzyme Inhibition
Q29. Enzymes are best defined as:
Answer: A — An enzyme is a catalyst of biological origin; it accelerates a cellular reaction without itself being permanently altered.
Enzymes
Q30. Raising the temperature well above the optimum reduces enzyme activity mainly because:
Answer: C — Above the optimum; the extra kinetic energy disrupts the weak hydrogen and ionic bonds holding the tertiary structure; the active site loses its shape and the enzyme is denatured.
Factors Affecting Enzyme Activity
Q31. The optimum temperature of an enzyme is the temperature at which:
Answer: C — Below this point the rate is limited by low kinetic energy and above it by denaturation; the greatest rate is therefore obtained at the optimum.
Factors that Affect the Rate of Enzyme Reactions
Q32. An enzyme inhibitor is a substance that:
Answer: B — An inhibitor combines with the enzyme in such a way that fewer molecules of substrate can be converted; the rate of the reaction therefore falls.
Inhibitors
Q33. The correct sequence of events in an enzyme catalysed reaction is:
Answer: D — The substrate first occupies the active site to give the ES complex; it is then changed into product, which leaves the site and sets the enzyme free.
Mode of Enzyme Action
Q34. Enzymes accelerate a reaction by acting on which thermodynamic quantity?
Answer: B — An enzyme provides an alternative pathway with a lower activation energy; so a far greater fraction of collisions become productive. It cannot alter the free energy change or the position of equilibrium.
Nature and Mechanism of Enzyme Action
Evolution
Q35. The age of the earth is estimated to be about:
Answer: C — Radiometric dating of the oldest meteorites and terrestrial rocks places the formation of the earth at roughly 4.6 billion years ago.
Concept of Evolution
Q36. Darwin published his theory of evolution by natural selection in the book:
Answer: B — On the Origin of Species appeared in 1859 and set out descent with modification through natural selection; Lamarck wrote Philosophie Zoologique and Lyell the Principles of Geology.
Darwinism
Q37. The central idea of Lamarck's theory of evolution was:
Answer: C — Lamarck held that organs strengthened by use and weakened by disuse pass those modifications to offspring; a mechanism later rejected because somatic changes do not enter the germ line.
Lamarckism
Q38. Natural selection acts directly upon which of the following?
Answer: C — Selection can only act on expressed characters; individuals with favourable phenotypes survive and reproduce more; and the underlying alleles increase in frequency indirectly.
Natural Selection
Q39. The Miller and Urey experiment demonstrated that:
Answer: A — Sparking a mixture of methane; ammonia; hydrogen and water vapour produced amino acids; showing that organic building blocks could form abiotically on the primitive Earth.
Origin of Life
Homeostasis
Q40. Urea is produced in the liver by the:
Answer: D — The urea cycle (ornithine cycle) in hepatocytes converts toxic ammonium ions (from amino acid deamination) into urea, which is transported to kidneys for excretion.
Excretion
Where to go next
These questions are a sample. The full Biology question bank is available in the topic-wise Biology practice tool, which lets you filter by chapter and tracks which questions you have already answered. If a question here exposed a gap, the MDCAT notes section covers the underlying theory chapter by chapter, and a full-length timed mock test is the best way to find out whether you can hold that accuracy under exam conditions.
Frequently asked questions
How many Biology questions are on the MDCAT 2026?
Biology accounts for 81 of the 180 MCQs on the MDCAT — 45% of the total paper. There is no negative marking, so every question should be attempted even when you are unsure.
Which Biology chapters carry the most weight?
Cell Structure & Function, Bioenergetics, Coordination & Control, Reproduction, and Evolution consistently generate the most questions. Smaller units such as Acellular Life and Biotechnology still appear, usually with one or two questions each.
Is FSc Biology enough for the MDCAT?
The PMDC curriculum is drawn from the FSc syllabus, so your textbooks cover the material. What FSc does not train is the format — 81 questions under timed conditions with four plausible options. That gap is what practice questions close.