Biology is the single most important subject in the MDCAT exam. With 80 MCQs carrying 40% of the total marks, it can make or break your medical entrance score. The good news? PMC tends to repeat concepts — and sometimes even exact questions — across years.
We analyzed MDCAT papers from 2008 to 2025 and identified the 50 most frequently tested Biology MCQs. These questions cover the core concepts that PMC examiners love to test again and again. Mastering them gives you a guaranteed head start.
MDCAT Biology at a Glance: 80 MCQs | 40% weightage | 16 chapters from FSc Part-I & Part-II | Mostly recall-based with increasing application-type questions since 2022.
Chapter-wise Frequency Analysis
Not all chapters are created equal. Some chapters appear far more frequently than others. Here is the approximate MCQ distribution based on past paper trends:
| Chapter | Approx. MCQs per Paper | Frequency |
|---|---|---|
| Cell Structure and Function | 6–8 | Very High |
| Biological Molecules | 6–8 | Very High |
| Enzymes | 4–5 | High |
| Coordination and Control | 6–8 | Very High |
| Variation and Genetics | 5–6 | High |
| Reproduction | 4–5 | High |
| Bio-Energetics | 4–5 | High |
| Evolution | 3–4 | Medium |
| Bio-Diversity | 4–5 | High |
| Biotechnology | 3–4 | Medium |
| Circulation | 4–5 | High |
| Immunity | 3–4 | Medium |
| Respiration | 3–4 | Medium |
| Digestion | 3–4 | Medium |
| Homeostasis | 3–4 | Medium |
| Support and Movement | 3–4 | Medium |
Cell Structure and Function
Chapter: Cell Structure and Function
Question 1
The fluid mosaic model of cell membrane was proposed by:
Explanation: Singer and Nicolson proposed the fluid mosaic model in 1972, describing the cell membrane as a dynamic structure with proteins floating in a fluid phospholipid bilayer.
Chapter: Cell Structure and Function
Question 2
Which organelle is known as the "powerhouse of the cell"?
Explanation: Mitochondria are called the powerhouse of the cell because they produce ATP through oxidative phosphorylation during cellular respiration.
Chapter: Cell Structure and Function
Question 3
Centrioles are absent in the cells of:
Explanation: Higher plants lack centrioles. During cell division, spindle fibres in plant cells are formed without centrioles, organized by other microtubule-organizing centres.
Chapter: Cell Structure and Function
Question 4
The 9+2 arrangement of microtubules is found in:
Explanation: Cilia and flagella have a 9+2 arrangement (9 peripheral doublets + 2 central singlets). Centrioles and basal bodies have 9+0 arrangement (9 triplets, no central microtubules).
Biological Molecules
Chapter: Biological Molecules
Question 5
The bond between two amino acids is called:
Explanation: A peptide bond is a covalent bond formed between the amino group (–NH2) of one amino acid and the carboxyl group (–COOH) of another, with the release of a water molecule (condensation reaction).
Chapter: Biological Molecules
Question 6
Which of the following is a disaccharide?
Explanation: Lactose (milk sugar) is a disaccharide composed of glucose and galactose. Glucose, fructose, and galactose are all monosaccharides.
Chapter: Biological Molecules
Question 7
The tertiary structure of protein is maintained by:
Explanation: The tertiary structure involves 3D folding of the polypeptide chain stabilized by multiple types of bonds including disulphide bridges, hydrophobic interactions, ionic bonds, and hydrogen bonds between R-groups.
Chapter: Biological Molecules
Question 8
Which lipid is a major component of the cell membrane?
Explanation: Phospholipids are the primary structural component of cell membranes. They are amphipathic — having a hydrophilic head and two hydrophobic fatty acid tails — forming the bilayer.
Enzymes
Chapter: Enzymes
Question 9
The lock and key model of enzyme action was proposed by:
Explanation: Emil Fischer proposed the lock and key model in 1894, suggesting that the enzyme's active site (lock) has a rigid shape complementary to the substrate (key). Koshland later proposed the induced fit model.
Chapter: Enzymes
Question 10
A non-protein part of an enzyme that is loosely attached is called:
Explanation: A coenzyme is an organic non-protein cofactor that is loosely (reversibly) bound to the enzyme. A prosthetic group is tightly (permanently) bound. The protein part alone is the apoenzyme; together they form the holoenzyme.
Chapter: Enzymes
Question 11
Competitive inhibitors of enzymes work by:
Explanation: Competitive inhibitors have a shape similar to the substrate and compete for the enzyme's active site. Their effect can be overcome by increasing substrate concentration.
Bio-Energetics
Chapter: Bio-Energetics
Question 12
The net gain of ATP molecules during glycolysis is:
Explanation: Glycolysis produces 4 ATP by substrate-level phosphorylation but consumes 2 ATP in the energy investment phase. Therefore, the net gain is 2 ATP per glucose molecule.
Chapter: Bio-Energetics
Question 13
In photosynthesis, the light reactions take place in the:
Explanation: Light reactions (photophosphorylation) occur on the thylakoid membranes where photosystems I and II, electron carriers, and ATP synthase are located. The Calvin cycle (dark reactions) occurs in the stroma.
Chapter: Bio-Energetics
Question 14
The CO2 acceptor in the Calvin cycle is:
Explanation: RuBP (a 5-carbon compound) is the CO2 acceptor in the Calvin cycle. The enzyme RuBisCO catalyses the fixation of CO2 to RuBP, producing two molecules of 3-PGA.
Coordination and Control
Chapter: Coordination and Control
Question 15
The part of the brain that controls body temperature, hunger, and thirst is the:
Explanation: The hypothalamus is the main homeostatic control centre of the brain. It regulates body temperature, hunger, thirst, sleep, and also controls the pituitary gland.
Chapter: Coordination and Control
Question 16
Which hormone is secreted by the adrenal medulla during stress?
Explanation: The adrenal medulla secretes adrenaline (epinephrine) and noradrenaline during the fight-or-flight response. Cortisol and aldosterone are secreted by the adrenal cortex.
Chapter: Coordination and Control
Question 17
The neurotransmitter released at neuromuscular junctions is:
Explanation: Acetylcholine is the neurotransmitter at neuromuscular junctions. It binds to receptors on the muscle fibre membrane, triggering muscle contraction.
Chapter: Coordination and Control
Question 18
Diabetes insipidus is caused by the deficiency of:
Explanation: Diabetes insipidus results from a deficiency of ADH (vasopressin) from the posterior pituitary. It leads to excessive dilute urine and extreme thirst. Diabetes mellitus is related to insulin.
Chapter: Coordination and Control
Question 19
The resting membrane potential of a neuron is approximately:
Explanation: The resting membrane potential of a typical neuron is approximately -70 mV, maintained by the sodium-potassium pump (3 Na+ out, 2 K+ in) and selective ion permeability.
Variation and Genetics
Chapter: Variation and Genetics
Question 20
A person with blood group AB has the genotype:
Explanation: Blood group AB is an example of codominance. Both alleles IA and IB are expressed equally, producing both A and B antigens on red blood cells.
Chapter: Variation and Genetics
Question 21
Colour blindness is a sex-linked recessive trait. A carrier mother and a normal father will have what percentage of colour-blind sons?
Explanation: If the mother is a carrier (XCX) and the father is normal (XY), then 50% of sons will receive XC from the mother and be colour-blind (XCY), while 50% will be normal (XY).
Chapter: Variation and Genetics
Question 22
Down syndrome is caused by trisomy of chromosome number:
Explanation: Down syndrome (trisomy 21) results from three copies of chromosome 21, giving a total of 47 chromosomes. It is the most common autosomal aneuploidy. Trisomy 13 is Patau syndrome, and trisomy 18 is Edwards syndrome.
Chapter: Variation and Genetics
Question 23
Crossing over occurs during which stage of meiosis?
Explanation: Crossing over occurs during prophase I of meiosis (specifically the pachytene stage) when homologous chromosomes form bivalents and exchange genetic material at chiasmata, increasing genetic variation.
Reproduction
Chapter: Reproduction
Question 24
The hormone responsible for maintaining the uterine lining during early pregnancy is:
Explanation: Progesterone, initially secreted by the corpus luteum and later by the placenta, maintains the thick, vascularized uterine lining (endometrium) essential for embryo implantation and early pregnancy.
Chapter: Reproduction
Question 25
Double fertilization is a characteristic feature of:
Explanation: Double fertilization is unique to angiosperms (flowering plants). One sperm fuses with the egg to form the zygote (2n), and the second sperm fuses with two polar nuclei to form the triploid endosperm (3n).
Chapter: Reproduction
Question 26
The acrosome of a sperm cell is derived from the:
Explanation: The acrosome is a cap-like structure at the head of the sperm derived from the Golgi apparatus. It contains hydrolytic enzymes (like hyaluronidase) that help the sperm penetrate the egg's outer layers.
Bio-Diversity
Chapter: Bio-Diversity
Question 27
Bacteria lack a true nucleus and are classified as:
Explanation: Bacteria are prokaryotes — they lack a membrane-bound nucleus and other membrane-bound organelles. Their genetic material (circular DNA) lies in the nucleoid region of the cytoplasm.
Chapter: Bio-Diversity
Question 28
Which of the following is a characteristic feature of Kingdom Fungi?
Explanation: Fungi are eukaryotic, heterotrophic organisms with cell walls made of chitin. They absorb nutrients externally (absorptive heterotrophy) and reproduce by spores.
Chapter: Bio-Diversity
Question 29
The binomial nomenclature system was introduced by:
Explanation: Carolus Linnaeus introduced the binomial nomenclature system in which each species is given a two-part Latin name — the genus name (capitalized) and the species name (lowercase), e.g., Homo sapiens.
Evolution
Chapter: Evolution
Question 30
Homologous organs provide evidence for:
Explanation: Homologous organs have the same basic structural plan and origin but different functions (e.g., human arm, whale flipper, bat wing). They are evidence of divergent evolution from a common ancestor.
Chapter: Evolution
Question 31
The "survival of the fittest" concept was proposed by:
Explanation: The phrase "survival of the fittest" was coined by Herbert Spencer after reading Darwin's work. Darwin later used the term in the 5th edition of On the Origin of Species as an alternative to natural selection.
Circulation
Chapter: Circulation
Question 32
The pacemaker of the heart is:
Explanation: The SA node, located in the right atrium, is the natural pacemaker. It generates electrical impulses at a rate of about 70–80 beats per minute, initiating each heartbeat.
Chapter: Circulation
Question 33
Which blood vessel carries oxygenated blood from the lungs to the heart?
Explanation: Pulmonary veins carry oxygenated blood from the lungs to the left atrium of the heart. The pulmonary artery carries deoxygenated blood from the right ventricle to the lungs.
Chapter: Circulation
Question 34
Universal blood donor group is:
Explanation: Blood group O is the universal donor because O-type red blood cells have no A or B antigens on their surface, so they do not trigger an immune response in any recipient. AB is the universal recipient.
Immunity
Chapter: Immunity
Question 35
Which type of immunity is provided by vaccination?
Explanation: Vaccination provides artificial active immunity. The vaccine contains weakened or dead pathogens/antigens that stimulate the body to produce its own antibodies and memory cells without causing disease.
Chapter: Immunity
Question 36
Antibodies are produced by:
Explanation: B-lymphocytes differentiate into plasma cells that produce and secrete antibodies (immunoglobulins). T-lymphocytes are involved in cell-mediated immunity and help activate B-cells.
Respiration
Chapter: Respiration
Question 37
The exchange of gases in the lungs occurs at the:
Explanation: Gas exchange occurs in the alveoli — tiny, thin-walled air sacs surrounded by dense capillary networks. Oxygen diffuses into the blood and carbon dioxide diffuses out across the one-cell-thick alveolar walls.
Chapter: Respiration
Question 38
Most of the CO2 is transported in the blood as:
Explanation: About 70% of CO2 is transported as bicarbonate ions (HCO3-) in the plasma. CO2 combines with water in RBCs (catalysed by carbonic anhydrase) to form carbonic acid, which dissociates into H+ and HCO3-.
Digestion
Chapter: Digestion
Question 39
Pepsin works best in which pH environment?
Explanation: Pepsin is a stomach enzyme that digests proteins. It functions optimally at pH 1.5–2.5, which is maintained by hydrochloric acid (HCl) secreted by parietal cells of the gastric glands.
Chapter: Digestion
Question 40
Bile is produced by the liver and stored in the:
Explanation: Bile is produced by hepatocytes (liver cells) and stored and concentrated in the gallbladder. When fatty food enters the duodenum, cholecystokinin (CCK) stimulates the gallbladder to release bile for fat emulsification.
Chapter: Digestion
Question 41
The primary site of nutrient absorption in the digestive system is the:
Explanation: The small intestine (especially the jejunum and ileum) is the primary site of nutrient absorption. Its surface area is enormously increased by circular folds, villi, and microvilli.
Homeostasis
Chapter: Homeostasis
Question 42
The functional unit of the kidney is:
Explanation: The nephron is the structural and functional unit of the kidney. Each kidney contains about 1 million nephrons. It consists of the Bowman's capsule, proximal tubule, loop of Henle, distal tubule, and collecting duct.
Chapter: Homeostasis
Question 43
Which of the following is the main nitrogenous waste in humans?
Explanation: Humans are ureotelic — urea is the primary nitrogenous waste product. It is produced in the liver through the ornithine cycle (urea cycle) from ammonia generated by amino acid deamination.
Support and Movement
Chapter: Support and Movement
Question 44
The protein responsible for muscle contraction is:
Explanation: Muscle contraction occurs through the sliding filament mechanism involving both actin (thin filaments) and myosin (thick filaments). Myosin heads bind to actin and pull the filaments past each other, shortening the sarcomere.
Chapter: Support and Movement
Question 45
Osteoporosis is caused by the deficiency of:
Explanation: Osteoporosis is a condition of weakened, brittle bones caused primarily by calcium deficiency and lack of vitamin D (which aids calcium absorption). It is most common in postmenopausal women due to decreased estrogen levels.
Biotechnology
Chapter: Biotechnology
Question 46
Restriction enzymes are used in genetic engineering to:
Explanation: Restriction endonucleases (restriction enzymes) act as "molecular scissors" — they cut DNA at specific palindromic recognition sequences. DNA ligase is the enzyme that joins DNA fragments together.
Chapter: Biotechnology
Question 47
PCR (Polymerase Chain Reaction) is used to:
Explanation: PCR is a technique that amplifies (makes millions of copies of) a specific DNA segment in vitro. It uses Taq DNA polymerase (a heat-stable enzyme), primers, nucleotides, and repeated cycles of denaturation, annealing, and extension.
Chapter: Biotechnology
Question 48
The vector most commonly used in genetic engineering is:
Explanation: Plasmids are small, circular, double-stranded DNA molecules found in bacteria. They are the most commonly used vectors in genetic engineering because they can self-replicate and carry foreign DNA into host cells.
Additional High-Yield MCQs
Chapter: Biological Molecules
Question 49
The DNA molecule is a double helix held together by:
Explanation: The two strands of DNA are held together by hydrogen bonds between complementary base pairs — adenine pairs with thymine (2 H-bonds), and guanine pairs with cytosine (3 H-bonds).
Chapter: Bio-Energetics
Question 50
During aerobic respiration, the Krebs cycle takes place in the:
Explanation: The Krebs cycle (citric acid cycle) occurs in the mitochondrial matrix. Glycolysis occurs in the cytoplasm, and the electron transport chain is located on the inner mitochondrial membrane.
Tips for Scoring High in MDCAT Biology
Biology is the highest-scoring subject if you prepare strategically. Here are proven tips from top scorers:
- Master the diagrams. PMC frequently tests labelling and identification — heart structure, nephron, brain parts, cell organelles. Draw and label them repeatedly until you can do it from memory.
- Focus on high-yield chapters first. Cell Structure, Biological Molecules, Coordination and Control, and Variation and Genetics collectively make up nearly 40% of the Biology paper. Prioritize these.
- Memorize key values and numbers. Resting membrane potential (-70 mV), ATP yield from glycolysis (net 2), chromosome numbers for common disorders (trisomy 21, 13, 18), pH values for enzymes — these are tested every year.
- Understand, do not just memorize. Application-based MCQs are increasing. Understand the "why" behind processes like crossing over, codominance, enzyme inhibition, and hormonal feedback loops.
- Solve past papers extensively. After completing your syllabus, solve MDCAT papers from 2017 onwards (PMC era). You will notice the same concepts repeating in different question formats.
- Revise with MCQs, not textbooks. In the final month, shift from reading textbook chapters to solving MCQs. This trains your brain for the exam format and improves speed.
- Do not ignore any chapter. Even "low-yield" chapters like Evolution or Support and Movement can give you 3–4 easy marks. In a competitive exam, every mark counts.
- Use elimination strategy. When unsure, eliminate obviously wrong options first. In Biology MCQs, usually 2 options can be eliminated quickly, giving you a 50/50 chance.
Pro Tip: Create flashcards for hormones and their functions, vitamins and deficiency diseases, and scientists and their discoveries. These three categories appear in almost every MDCAT paper.
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