PAK-MED STUDY CORNER MDCAT

 

MDCAT 2019 Biology Past Paper Solved | MCQs 1-50

Total MCQs: 50 | Time: 210 Minutes | No Negative Marking

1. In chemiosmosis the proton (H+) pumps moves from ________

A. Stroma to Lumen

B. Stroma to cytoplasm

C. Lumen to Stroma

D. Cytoplasm to Stroma

Correct Answer: C. Lumen to Stroma

Explanation: Protons move from higher concentration lumen to lower concentration stroma.

2. Microtubule subunits for spindle fibers are synthesized in ________ phase.

A. G2

B. M

C. S

D. G1

Correct Answer: A. G2

Explanation: G2 phase prepares for mitosis. Microtubule subunits synthesized here.

3. If stimulation is above _________, impulses travel to brain along sensory neuron.

A. Action Potential

B. Threshold

C. Resting Potential

D. Recovery Period

Correct Answer: B. Threshold

Explanation: At threshold, Na+ gates open and impulse travels.

4. Substances increasing hypothalamus set point are called:

A. Pepsin

B. Pyrogens

C. Prions

D. Androgens

Correct Answer: B. Pyrogens

Explanation: Pyrogens raise body temperature set point, causing fever.

5. During inspiration chest cavity space increases due to:

A. Increased pressure

B. Relaxation of diaphragm

C. Relaxation external intercostals

D. Contraction of diaphragm

Correct Answer: D. Contraction of diaphragm

Explanation: Diaphragm flattens, increasing thoracic volume.

6. Hormone stimulating ovulation?

A. LH

B. FSH

C. Estrogen

D. Progesterone

Correct Answer: A. LH

Explanation: LH surge causes ovulation from follicle.

7. Bond between 2 monosaccharides is:

A. Carboxyl

B. Hydroxyl

C. Hydrogen

D. Glycosidic

Correct Answer: D. Glycosidic bond

Explanation: Glycosidic bond forms by removing water.

8. Site of protein synthesis?

A. Ribosomes

B. Lysosomes

C. Golgi

D. Cisternae

Correct Answer: A. Ribosomes

Explanation: Ribosomes synthesize proteins.

9. Water movement via plasmodesmata is:

A. Symplastic

B. Mineral pathway

C. Vacuolar

D. Apoplastic

Correct Answer: A. Symplastic pathway

Explanation: Symplast = through cytoplasm via plasmodesmata.

10. Part C of nephron without vascular supply is?

A. Collecting tubule

B. Proximal tubule

C. Distal tubule

D. Loop of Henle

Correct Answer: D. Loop of Henle

Explanation: Loop of Henle is the U-shaped part.

11. Xerophytes have small thick leaves to:

A. Float on water

B. Survive in salt

C. Limit water loss

D. Increase water loss

Correct Answer: C. Limit water loss

Explanation: Less surface area = less transpiration.

12. Organelle with circular DNA like bacteria?

A. Ribosome

B. Lysosome

C. Chloroplast

D. Nucleus

Correct Answer: C. Chloroplast

Explanation: Chloroplast and mitochondria have circular DNA.

13. Two heterozygous for sickle cell. % affected homozygotes?

A. 50%

B. 25%

C. 75%

D. 100%

Correct Answer: B. 25%

Explanation: Ss x Ss = 1 SS : 2 Ss : 1 ss = 25% ss.

14. Route of urine excretion?

A. Kidney-ureter-bladder-urethra

B. Bladder-kidney-ureter-urethra

C. Kidney-ureter-urethra-bladder

D. Kidney-urethra-bladder-ureter

Correct Answer: A. Kidney – ureter – urinary bladder – urethra

Explanation: Standard urinary tract sequence.

15. Phase where sister chromatids move to poles?

A. Prophase

B. Anaphase

C. Telophase

D. Metaphase

Correct Answer: B. Anaphase

Explanation: Anaphase = chromatids separate.

16. Plasmid pBR322 has resistance for:

A. Tetracycline + Doxycycline

B. Streptomycin

C. Doxy + Ampicillin

D. Ampicillin + Tetracycline

Correct Answer: D. Ampicillin and Tetracycline

Explanation: pBR322 = Amp^r and Tet^r genes.

17. Purine bases are:

A. G + C

B. A, G, C

C. A + G

D. A + T

Correct Answer: C. Adenine and Guanine

Explanation: Purines = A, G. Pyrimidines = C, T/U.

18. Calvin cycle missing step is:

A. Hydrogenase

B. Oxaloacetate

C. Ribulose bisphosphate

D. Pyruvate

Correct Answer: C. Ribulose bisphosphate

Explanation: CO2 fixes with RuBP in Calvin cycle.

19. Taq polymerase from Thermus aquaticus because:

A. Withstands high temp

B. Withstands low temp

C. Works fast

D. Reusable

Correct Answer: A. It can withstand high denaturation temperature

Explanation: Thermostable enzyme for PCR.

20. Energy reduced by enzymes is:

A. Light

B. Activation energy

C. Active energy

D. Heat

Correct Answer: B. Activation energy

Explanation: Enzymes lower Ea of reactions.

21. Ca2+ function in muscle contraction?

A. Binds troponin

B. Nerve impulse

C. Polarize light

D. Binds tropomyosin

Correct Answer: A. Bind to troponin

Explanation: Ca2+ binds troponin, exposing myosin sites.

22. Common in competitive + non-competitive inhibition?

A. Irreversible

B. Feedback

C. Reversible

D. Non-reversible

Correct Answer: C. Reversible Inhibition

Explanation: Both types are usually reversible.

23. Primary oocyte divides to secondary oocyte + ?

A. Polar body

B. Oogonium

C. Follicle cell

D. Ovum

Correct Answer: A. Polar body

Explanation: Meiosis I gives secondary oocyte + 1st polar body.

24. Homozygous means:

A. Two identical alleles

B. Two identical genes

C. Alleles

D. Two different alleles

Correct Answer: A. having two identical alleles

Explanation: AA or aa = homozygous.

25. Hormones maintaining endometrium for implantation?

A. LH + Progesterone

B. Estrogen + FSH

C. LH + FSH

D. Estrogen + Progesterone

Correct Answer: D. Estrogen and progesterone

Explanation: Both make endometrium receptive.

26. Animals store carbohydrate as:

A. Glucose

B. Glycogen

C. Galactose

D. Glucagon

Correct Answer: B. Glycogen

Explanation: Glycogen in liver and muscles.

27. Polio vaccine contains _____ for immunity:

A. Antisera

B. Antibodies

C. Antibiotics

D. Antigen

Correct Answer: D. Antigen

Explanation: Vaccine gives antigen to make antibodies.

28. Blood vessels with semilunar valves?

A. Arteries

B. Veins

C. Arterioles

D. Capillaries

Correct Answer: A. Arteries

Explanation: Aorta and pulmonary artery have semilunar valves.

29. Main neurotransmitter outside CNS?

A. Choline

B. Acetylcholine

C. Acetaldehyde

D. Phosphatidylcholine

Correct Answer: B. Acetylcholine

Explanation: ACh at neuromuscular junctions.

30. Thick filaments are made of:

A. Hemoglobin

B. Myoglobin

C. Actin

D. Myosin

Correct Answer: D. Myosin

Explanation: Thick filament = myosin.

31. Prokaryotic ribosome size?

A. 40S

B. 70S

C. 65S

D. 60S

Correct Answer: B. 70S

Explanation: 50S + 30S = 70S in prokaryotes.

32. Eukaryotic but not prokaryotic?

A. Nucleus

B. DNA

C. Ribosomes

D. Cell membrane

Correct Answer: A. Nucleus

Explanation: Nucleus absent in prokaryotes.

33. RNA polymerase makes mRNA copy = ?

A. Proof reading

B. DNA Replication

C. Transcription

D. Translation

Correct Answer: C. Transcription

Explanation: DNA → mRNA.

34. Alcohol + acetic acid gives?

A. Glucose + O2

B. Glycogen + H2O

C. Ester + H2O

D. Glycerol + H2SO4

Correct Answer: C. An ester and water

Explanation: Esterification reaction.

35. Locus refers to _____ of gene?

A. Frequency

B. Copy

C. Position

D. Inversion

Correct Answer: C. Position

Explanation: Locus = gene position on chromosome.

36. 15μm object, 5X eyepiece + 10X objective. Magnified size?

A. 250 μm

B. 50 μm

C. 750 μm

D. 500 μm

Correct Answer: C. 750 μm

Explanation: 5×10=50X. 15×50=750μm.

37. Enzyme for SCID?

A. Pancreatic enzyme

B. ADA

C. β-galactosidase

D. β-lactamase

Correct Answer: B. Adenosine Deaminase (ADA)

Explanation: ADA deficiency causes SCID.

38. Change in allele frequency by chance?

A. Natural selection

B. Migration

C. Mutation

D. Genetic drift

Correct Answer: D. Genetic drift

Explanation: Random changes in small populations.

39. Inner membrane infoldings of mitochondria?

A. Matrix

B. Porin

C. Cristae

D. Ribosomes

Correct Answer: C. Cristae

Explanation: Cristae increase surface area.

40. Main nitrogenous waste in humans?

A. Uric acid

B. Ammonia

C. Urea

D. Ammonium

Correct Answer: C. Urea

Explanation: Humans are ureotelic.

41. Smooth ER metabolizes?

A. Carbs

B. Proteins

C. Nucleic acids

D. Lipids

Correct Answer: D. Lipids

Explanation: Smooth ER makes lipids/steroids.

42. Acetylcholine + Noradrenaline are?

A. Hormones

B. Channel proteins

C. Enzymes

D. Neurotransmitters

Correct Answer: D. Neurotransmitters

Explanation: Chemical messengers at synapse.

43. Reflex involves only?

A. Brain, receptor, spinal cord

B. Receptor, effector, spinal cord

C. Receptor, neuron, brain

D. Receptor + effector

Correct Answer: B. receptors, effectors and spinal cord

Explanation: Reflex arc bypasses brain.

44. Genes not assorted independently when?

A. Not linked, far apart

B. Too many genes

C. Mutated genes

D. Linked, close together

Correct Answer: D. When genes are linked

Explanation: Linked genes violate independent assortment.

45. Got infection, survived. Immunity type?

A. Natural active

B. Artificial active

C. Active

D. Passive

Correct Answer: A. Naturally induced active immunity

Explanation: Illness + recovery = natural active.

46. Haploid cells maturing into sperm?

A. Secondary spermatocytes

B. Primary spermatocytes

C. Spermatogonia

D. Spermatids

Correct Answer: D. Spermatids

Explanation: Spermatids → spermatozoa.

47. Transgenic mice used to produce?

A. Protein rich milk

B. Growth hormone

C. Protein rich meat

D. Extra hair

Correct Answer: B. A growth hormone

Explanation: Mice with extra hair due to GH gene.

48. Natural selection: organisms produce?

A. More offspring than supported

B. Less offspring

C. As per resources

D. To create resources

Correct Answer: A. More offspring than supported

Explanation: Overproduction leads to selection.

49. Reaction centers have _____ molecules:

A. ATP

B. Chlorophyll

C. Glucose

D. Carotenoids

Correct Answer: B. Chlorophyll

Explanation: P680 and P700 chlorophyll.

50. N15 to N14, 2 rounds replication gives?

A. 50% hybrid + 50% light

B. 50% hybrid + 50% heavy

C. 100% heavy

D. 100% hybrid

Correct Answer: A. 50% hybrid duplex and 50% light duplex

Explanation: Semi-conservative replication.