MDCAT Biology MCQs with Answers Set 1

MDCAT Biology MCQs with Answers

Medical and Dental College Admission Test (MDCAT) — Biology Section

 

This collection of 50 MDCAT Biology MCQs covers the most frequently tested topics in the MDCAT Biology section, including cell biology, genetics, physiology, biochemistry, and ecology. Each question includes four options, the correct answer highlighted in green, and a concise explanation to reinforce your understanding. Ideal for MDCAT aspirants preparing for the National Medical and Dental College Admissions Test conducted by Pakistan Medical Commission (PMC).

How to Use This Document

– Read each question carefully before looking at the answer.

– The correct answer is shown in green and bold.

– Read the explanation after each answer to understand the concept.

 

Q1. Which organelle is known as the powerhouse of the cell?

  1. Nucleus
  2. Ribosome
  3. Mitochondria
  4. Golgi apparatus

Correct Answer: C. Mitochondria

Explanation: Mitochondria produce ATP through cellular respiration, supplying energy to the cell. They contain their own DNA and double membrane.

 

Q2. The basic unit of life is the:

  1. Tissue
  2. Organ
  3. Cell
  4. Molecule

Correct Answer: C. Cell

Explanation: The cell is the smallest structural and functional unit of all living organisms, as established by cell theory.

 

Q3. Which type of cell division produces gametes?

  1. Mitosis
  2. Meiosis
  3. Binary fission
  4. Budding

Correct Answer: B. Meiosis

Explanation: Meiosis reduces the chromosome number by half, producing haploid gametes (sperm and egg cells) for sexual reproduction.

 

Q4. DNA replication occurs during which phase of the cell cycle?

  1. G1 phase
  2. S phase
  3. G2 phase
  4. M phase

Correct Answer: B. S phase

Explanation: DNA synthesis (replication) occurs during the S (synthesis) phase of interphase, before the cell enters mitosis or meiosis.

 

Q5. Which molecule carries genetic information from DNA to ribosomes?

  1. tRNA
  2. rRNA
  3. mRNA
  4. snRNA

Correct Answer: C. mRNA

Explanation: Messenger RNA (mRNA) is transcribed from DNA and carries the genetic code to ribosomes where proteins are synthesized.

 

Q6. The process by which plants make food using sunlight is called:

  1. Respiration
  2. Transpiration
  3. Photosynthesis
  4. Fermentation

Correct Answer: C. Photosynthesis

Explanation: Photosynthesis converts light energy, CO2, and water into glucose and oxygen. It occurs in chloroplasts containing chlorophyll.

 

Q7. Which blood cells are responsible for immunity?

  1. Erythrocytes
  2. Platelets
  3. Leukocytes
  4. Thrombocytes

Correct Answer: C. Leukocytes

Explanation: Leukocytes (white blood cells) are the key cells of the immune system, defending the body against infections and foreign substances.

 

Q8. The outermost layer of a plant cell is the:

  1. Cell membrane
  2. Cell wall
  3. Cytoplasm
  4. Vacuole

Correct Answer: B. Cell wall

Explanation: Plant cells have a rigid cell wall made of cellulose outside the cell membrane, providing structural support and protection.

 

Q9. Enzymes are biological molecules made of:

  1. Lipids
  2. Carbohydrates
  3. Nucleic acids
  4. Proteins

Correct Answer: D. Proteins

Explanation: Enzymes are protein catalysts that speed up biochemical reactions without being consumed. Their shape determines their function.

 

Q10. Which part of the brain controls breathing and heartbeat?

  1. Cerebrum
  2. Cerebellum
  3. Medulla oblongata
  4. Hypothalamus

Correct Answer: C. Medulla oblongata

Explanation: The medulla oblongata is the lowest part of the brainstem and controls vital autonomic functions including breathing, heart rate, and blood pressure.

 

Q11. The study of heredity and variation is called:

  1. Ecology
  2. Genetics
  3. Cytology
  4. Morphology

Correct Answer: B. Genetics

Explanation: Genetics is the branch of biology that studies genes, heredity, and genetic variation in living organisms.

 

Q12. Which vitamin is produced when skin is exposed to sunlight?

  1. Vitamin A
  2. Vitamin B12
  3. Vitamin C
  4. Vitamin D

Correct Answer: D. Vitamin D

Explanation: Ultraviolet (UV) rays from sunlight trigger the synthesis of Vitamin D in the skin. It is essential for calcium absorption and bone health.

 

Q13. In which organelle does protein synthesis occur?

  1. Mitochondria
  2. Ribosome
  3. Nucleus
  4. Lysosome

Correct Answer: B. Ribosome

Explanation: Ribosomes translate mRNA into polypeptide chains (proteins). They can be free in the cytoplasm or attached to the rough endoplasmic reticulum.

 

Q14. How many chromosomes are present in a normal human body cell?

  1. 23
  2. 44
  3. 46
  4. 48

Correct Answer: C. 46

Explanation: Human somatic (body) cells are diploid and contain 46 chromosomes arranged in 23 pairs. Gametes are haploid with 23 chromosomes.

 

Q15. Which of the following is NOT a function of the liver?

  1. Detoxification
  2. Bile production
  3. Insulin secretion
  4. Glycogen storage

Correct Answer: C. Insulin secretion

Explanation: Insulin is secreted by the beta cells of the pancreatic islets of Langerhans, not the liver. The liver stores glycogen and responds to insulin.

 

Q16. The functional unit of the kidney is the:

  1. Alveolus
  2. Nephron
  3. Neuron
  4. Sarcomere

Correct Answer: B. Nephron

Explanation: Each kidney contains approximately one million nephrons. The nephron filters blood, reabsorbs useful substances, and produces urine.

 

Q17. Oxygen is transported in blood mainly by:

  1. Plasma
  2. Platelets
  3. Hemoglobin
  4. White blood cells

Correct Answer: C. Hemoglobin

Explanation: Hemoglobin is an iron-containing protein in red blood cells that binds oxygen in the lungs and releases it in body tissues.

 

Q18. Which type of reproduction does not involve gametes?

  1. Sexual reproduction
  2. Asexual reproduction
  3. Fertilization
  4. Pollination

Correct Answer: B. Asexual reproduction

Explanation: Asexual reproduction produces offspring from a single parent without gametes. Examples include budding, binary fission, and vegetative propagation.

 

Q19. The site of gas exchange in the lungs is the:

  1. Trachea
  2. Bronchus
  3. Alveolus
  4. Bronchiole

Correct Answer: C. Alveolus

Explanation: Alveoli are tiny air sacs in the lungs with thin walls and rich blood supply, allowing rapid diffusion of O2 into blood and CO2 out.

 

Q20. Which hormone regulates blood glucose levels?

  1. Thyroxine
  2. Adrenaline
  3. Insulin
  4. Estrogen

Correct Answer: C. Insulin

Explanation: Insulin, secreted by the pancreas, lowers blood glucose by promoting its uptake into cells and conversion to glycogen for storage.

 

Q21. The light-absorbing pigment in plants is:

  1. Hemoglobin
  2. Chlorophyll
  3. Melanin
  4. Carotenoid

Correct Answer: B. Chlorophyll

Explanation: Chlorophyll is the primary photosynthetic pigment found in chloroplasts. It absorbs red and blue light and reflects green, giving plants their color.

 

Q22. Which part of the cell controls its activities?

  1. Vacuole
  2. Ribosome
  3. Nucleus
  4. Cytoplasm

Correct Answer: C. Nucleus

Explanation: The nucleus contains the cell’s DNA and directs cell activities including growth, metabolism, and reproduction by controlling gene expression.

 

Q23. A solution with pH less than 7 is considered:

  1. Neutral
  2. Basic
  3. Acidic
  4. Alkaline

Correct Answer: C. Acidic

Explanation: The pH scale runs from 0 to 14. Values below 7 indicate acidic solutions (higher H+ concentration), 7 is neutral, and above 7 is basic.

 

Q24. Which of the following is a monosaccharide?

  1. Sucrose
  2. Maltose
  3. Glucose
  4. Starch

Correct Answer: C. Glucose

Explanation: Glucose is a simple sugar (monosaccharide) and the primary energy source for cells. Sucrose and maltose are disaccharides; starch is a polysaccharide.

 

Q25. Transpiration in plants occurs mainly through:

  1. Roots
  2. Stomata
  3. Xylem
  4. Phloem

Correct Answer: B. Stomata

Explanation: Stomata are tiny pores on leaf surfaces that allow water vapor to escape during transpiration. They also facilitate gas exchange for photosynthesis.

 

Q26. The process of cell eating (engulfing solid particles) is called:

  1. Pinocytosis
  2. Exocytosis
  3. Phagocytosis
  4. Osmosis

Correct Answer: C. Phagocytosis

Explanation: Phagocytosis is endocytosis of solid particles by cells. White blood cells use it to engulf and destroy pathogens and cellular debris.

 

Q27. Which structure connects muscles to bones?

  1. Ligament
  2. Tendon
  3. Cartilage
  4. Fascia

Correct Answer: B. Tendon

Explanation: Tendons are tough fibrous connective tissues that connect muscles to bones. Ligaments connect bones to other bones at joints.

 

Q28. In which phase of mitosis do chromosomes align at the cell’s equator?

  1. Prophase
  2. Anaphase
  3. Metaphase
  4. Telophase

Correct Answer: C. Metaphase

Explanation: During metaphase, condensed chromosomes align along the metaphase plate (cell equator), attached to spindle fibers from both poles.

 

Q29. The chemical formula of glucose is:

  1. C6H12O6
  2. C12H22O11
  3. C6H10O5
  4. C2H5OH

Correct Answer: A. C6H12O6

Explanation: Glucose (C6H12O6) is a hexose monosaccharide. C12H22O11 is sucrose; C6H10O5 represents cellulose repeating units; C2H5OH is ethanol.

 

Q30. Which part of the neuron receives incoming signals?

  1. Axon
  2. Myelin sheath
  3. Dendrite
  4. Synaptic knob

Correct Answer: C. Dendrite

Explanation: Dendrites are branched extensions of a neuron that receive electrochemical signals from other neurons and transmit them toward the cell body.

 

Q31. Plasmolysis in plant cells occurs due to:

  1. Endosmosis
  2. Exosmosis
  3. Diffusion
  4. Active transport

Correct Answer: B. Exosmosis

Explanation: Plasmolysis occurs when plant cells lose water by exosmosis in a hypertonic solution, causing the cell membrane to shrink away from the cell wall.

 

Q32. Which blood group is the universal donor?

  1. A
  2. B
  3. AB
  4. O

Correct Answer: D. O

Explanation: Blood group O negative is the universal donor for red blood cells as it lacks A, B, and Rh antigens, reducing the risk of immune reactions.

 

Q33. The movement of water across a semipermeable membrane is called:

  1. Diffusion
  2. Active transport
  3. Osmosis
  4. Facilitated diffusion

Correct Answer: C. Osmosis

Explanation: Osmosis is the passive movement of water molecules from a region of high water potential (low solute concentration) to low water potential across a semipermeable membrane.

 

Q34. Which enzyme breaks down starch in the mouth?

  1. Pepsin
  2. Lipase
  3. Salivary amylase
  4. Trypsin

Correct Answer: C. Salivary amylase

Explanation: Salivary amylase (ptyalin) is secreted by salivary glands and begins starch digestion in the mouth by breaking it into maltose and dextrins.

 

Q35. The smallest bone in the human body is:

  1. Femur
  2. Stapes
  3. Patella
  4. Radius

Correct Answer: B. Stapes

Explanation: The stapes, one of three ossicles in the middle ear, is the smallest bone in the human body at about 3mm. It transmits sound vibrations to the inner ear.

 

Q36. Which part of the flower produces pollen?

  1. Pistil
  2. Sepal
  3. Anther
  4. Stigma

Correct Answer: C. Anther

Explanation: The anther is the pollen-producing part of the stamen (male reproductive organ of a flower). Pollen contains the male gametophytes.

 

Q37. The process of converting glucose to pyruvate is called:

  1. Krebs cycle
  2. Glycolysis
  3. Oxidative phosphorylation
  4. Gluconeogenesis

Correct Answer: B. Glycolysis

Explanation: Glycolysis is the first stage of cellular respiration occurring in the cytoplasm. It converts one glucose molecule into two pyruvate molecules, yielding 2 ATP.

 

Q38. Which type of tissue covers body surfaces?

  1. Connective tissue
  2. Muscle tissue
  3. Nervous tissue
  4. Epithelial tissue

Correct Answer: D. Epithelial tissue

Explanation: Epithelial tissue lines and covers body surfaces, organs, and cavities. It acts as a protective barrier and is involved in absorption, secretion, and sensation.

 

Q39. The hormone responsible for the fight-or-flight response is:

  1. Insulin
  2. Thyroxine
  3. Adrenaline (Epinephrine)
  4. Cortisol

Correct Answer: C. Adrenaline (Epinephrine)

Explanation: Adrenaline is secreted by the adrenal medulla in response to stress. It increases heart rate, dilates airways, and redirects blood to muscles.

 

Q40. Ribosomes are composed of:

  1. DNA and protein
  2. rRNA and protein
  3. mRNA and lipids
  4. tRNA and carbohydrates

Correct Answer: B. rRNA and protein

Explanation: Ribosomes consist of ribosomal RNA (rRNA) and proteins. They have two subunits (large and small) and serve as the site of protein synthesis.

 

Q41. The larynx is also known as the:

  1. Voice box
  2. Windpipe
  3. Food pipe
  4. Nasal cavity

Correct Answer: A. Voice box

Explanation: The larynx (voice box) contains the vocal cords and is responsible for sound production. It also prevents food from entering the airway during swallowing.

 

Q42. Which of the following is a fat-soluble vitamin?

  1. Vitamin C
  2. Vitamin B1
  3. Vitamin A
  4. Vitamin B12

Correct Answer: C. Vitamin A

Explanation: Fat-soluble vitamins include A, D, E, and K. They are stored in body fat and liver. Vitamins B and C are water-soluble and not stored long-term.

 

Q43. The Calvin cycle occurs in which part of the chloroplast?

  1. Thylakoid membrane
  2. Outer membrane
  3. Stroma
  4. Granum

Correct Answer: C. Stroma

Explanation: The Calvin cycle (light-independent reactions) takes place in the stroma of the chloroplast, using ATP and NADPH from the light reactions to fix CO2 into glucose.

 

Q44. Which structure in the eye focuses light on the retina?

  1. Cornea
  2. Iris
  3. Lens
  4. Pupil

Correct Answer: C. Lens

Explanation: The lens is a flexible, transparent structure that changes shape (accommodation) to focus light precisely onto the retina for clear vision.

 

Q45. Antibodies are produced by which cells?

  1. T lymphocytes
  2. B lymphocytes (plasma cells)
  3. Neutrophils
  4. Macrophages

Correct Answer: B. B lymphocytes (plasma cells)

Explanation: B lymphocytes, when activated, differentiate into plasma cells that produce specific antibodies (immunoglobulins) against antigens.

 

Q46. Which part of the digestive system absorbs most nutrients?

  1. Stomach
  2. Large intestine
  3. Small intestine
  4. Esophagus

Correct Answer: C. Small intestine

Explanation: The small intestine, especially the jejunum, is the primary site of nutrient absorption. Villi and microvilli greatly increase its surface area for absorption.

 

Q47. The backbone (vertebral column) is part of which skeletal division?

  1. Appendicular skeleton
  2. Axial skeleton
  3. Visceral skeleton
  4. Exoskeleton

Correct Answer: B. Axial skeleton

Explanation: The axial skeleton includes the skull, vertebral column, ribs, and sternum. The appendicular skeleton includes the limbs and girdles.

 

Q48. A dominant allele is represented by:

  1. Lowercase letter
  2. Uppercase letter
  3. Roman numeral
  4. Subscript number

Correct Answer: B. Uppercase letter

Explanation: In Mendelian genetics, dominant alleles are represented by uppercase letters (e.g., A) and recessive alleles by lowercase letters (e.g., a).

 

Q49. Which gas is released during photosynthesis?

  1. Carbon dioxide
  2. Nitrogen
  3. Hydrogen
  4. Oxygen

Correct Answer: D. Oxygen

Explanation: Oxygen is released as a byproduct of the light-dependent reactions when water molecules are split by photolysis during photosynthesis.

 

Q50. The term ‘homeostasis’ refers to:

  1. Cell division process
  2. Maintenance of stable internal conditions
  3. Hormone secretion
  4. Digestion of food

Correct Answer: B. Maintenance of stable internal conditions

Explanation: Homeostasis is the tendency of living systems to maintain stable internal conditions (e.g., body temperature, blood pH, glucose levels) despite external changes.

 

Q51. Which of the following is an example of a reflex action?

  1. Writing your name
  2. Solving a math problem
  3. Withdrawing hand from a hot object
  4. Reading a book

Correct Answer: C. Withdrawing hand from a hot object

Explanation: A reflex action is an automatic, rapid response to a stimulus that does not involve conscious thought. It is coordinated by the spinal cord, not the brain.

 

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