Biology MCQs

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Biology MCQs

Practice complete Biology MCQs covering Introduction to Biology, Cell Biology, Cell Structure, Cell Division, Biomolecules, Plant Physiology, Human Physiology, Genetics, Evolution, Biotechnology, Ecology, Classification of Living Organisms, Plant Kingdom, Animal Kingdom, Microbiology, Human Diseases, Nutrition, Reproduction, Environmental Biology, and all other important topics. Includes chapter-wise and exam-oriented multiple-choice questions with detailed answers and explanations for JKSSB, SSC, Banking, Railway, UPSC, CUET, NEET, State PSCs, and other competitive exams.

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Page 61 of 103
Question #1201
The structure that prevents backflow of blood from the left ventricle to the left atrium is the:
A. Pulmonary valve
B. Aortic valve
C. Tricuspid valve
D. Mitral valve
Discuss
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Correct Answer: Option D

Explanation:
The bicuspid (mitral) valve has two cusps and closes during ventricular systole to prevent regurgitation into the left atrium. The tricuspid valve is on the right.
This question belongs to: Science Biology
Question #1202
The disease caused by the bacterium Treponema pallidum is:
A. Syphilis
B. Gonorrhea
C. Chancroid
D. Chlamydia
Discuss
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Correct Answer: Option A

Explanation:
Syphilis is a sexually transmitted infection caused by the spirochete Treponema pallidum. Gonorrhea is Neisseria gonorrhoeae, chlamydia Chlamydia trachomatis.
This question belongs to: Science Biology
Question #1203
The organelle that contains enzymes for the glyoxylate cycle in plants is the:
A. Mitochondria
B. Chloroplast
C. Glyoxysome
D. Peroxisome
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Correct Answer: Option C

Explanation:
Glyoxysomes are specialized peroxisomes in oil-storing seeds that contain glyoxylate cycle enzymes, converting lipids to carbohydrates during germination.
This question belongs to: Science Biology
Question #1204
The vitamin that is required for the synthesis of clotting factors II, VII, IX, X is:
A. Vitamin E
B. Vitamin K
C. Vitamin C
D. Vitamin A
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Correct Answer: Option B

Explanation:
Vitamin K is a cofactor for γ-glutamyl carboxylase, which modifies glutamate residues in clotting factors, enabling calcium binding and coagulation.
This question belongs to: Science Biology
Question #1205
The scientist who proposed the 'chemiosmotic hypothesis' for ATP synthesis was:
A. Hans Krebs
B. Melvin Calvin
C. Fritz Lipmann
D. Peter Mitchell
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Correct Answer: Option D

Explanation:
Peter Mitchell proposed the chemiosmotic theory (1961), explaining that a proton gradient across a membrane drives ATP synthesis. Krebs discovered the citric acid cycle, Calvin the Calvin cycle, Lipmann discovered coenzyme A.
This question belongs to: Science Biology
Question #1206
The pigment that is the primary photosynthetic pigment in cyanobacteria is:
A. Fucoxanthin
B. Chlorophyll b
C. Chlorophyll a
D. Phycocyanin
Discuss
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Correct Answer: Option C

Explanation:
Cyanobacteria contain chlorophyll a (like plants) along with phycobilins (phycocyanin and phycoerythrin). Chlorophyll b is in green plants, phycocyanin is an accessory pigment.
This question belongs to: Science Biology
Question #1207
The process by which the embryo attaches to the uterine wall is:
A. Ovulation
B. Fertilization
C. Implantation
D. Menstruation
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Correct Answer: Option C

Explanation:
Implantation occurs about 6-7 days after fertilization, when the blastocyst embeds into the endometrium. Fertilization is sperm-egg fusion, ovulation egg release, menstruation shedding.
This question belongs to: Science Biology
Question #1208
The enzyme that catalyzes the conversion of ATP to cAMP is:
A. Phosphodiesterase
B. Adenylyl cyclase
C. Phospholipase C
D. Protein kinase A
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Correct Answer: Option B

Explanation:
Adenylyl cyclase converts ATP to cyclic AMP (cAMP), a second messenger. Phosphodiesterase breaks down cAMP, PKA is activated by cAMP, PLC produces IP₃ and DAG.
This question belongs to: Science Biology
Question #1209
The disease caused by the bacterium Bordetella pertussis is:
A. Scarlet fever
B. Tetanus
C. Diphtheria
D. Whooping cough
Discuss
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Correct Answer: Option D

Explanation:
Pertussis (whooping cough) is a respiratory infection characterized by severe coughing fits. Diphtheria is Corynebacterium, tetanus Clostridium, scarlet fever Streptococcus.
This question belongs to: Science Biology
Question #1210
The structure that controls the entry of light into the eye by adjusting pupil size is the:
A. Retina
B. Cornea
C. Lens
D. Iris
Discuss
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Correct Answer: Option D

Explanation:
The iris contains smooth muscle fibers (sphincter and dilator) that regulate the diameter of the pupil. The cornea and lens focus light, retina senses it.
This question belongs to: Science Biology
Question #1211
The vitamin that is essential for the synthesis of collagen is:
A. Vitamin A
B. Vitamin D
C. Vitamin B₁₂
D. Vitamin C
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Correct Answer: Option D

Explanation:
Vitamin C is a cofactor for prolyl and lysyl hydroxylases in collagen synthesis. Deficiency leads to impaired wound healing and scurvy.
This question belongs to: Science Biology
Question #1212
The technique used to introduce foreign DNA into cells by applying a brief electric pulse is:
A. Microinjection
B. Lipofection
C. Biolistics
D. Electroporation
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Correct Answer: Option D

Explanation:
Electroporation creates transient pores in the cell membrane using an electric field, allowing DNA to enter. Microinjection uses a fine needle, biolistics a gene gun, lipofection lipid vesicles.
This question belongs to: Science Biology
Question #1213
The hormone that stimulates the release of growth hormone from the pituitary is:
A. Dopamine
B. Somatostatin
C. Growth hormone-releasing hormone (GHRH)
D. Cortisol
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Correct Answer: Option C

Explanation:
GHRH, from the hypothalamus, stimulates the anterior pituitary to secrete growth hormone. Somatostatin inhibits GH release. Dopamine inhibits prolactin.
This question belongs to: Science Biology
Question #1214
The scientist who discovered the phenomenon of transformation in bacteria was:
A. Avery
B. Griffith
C. Chase
D. Hershey
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Correct Answer: Option B

Explanation:
Frederick Griffith in 1928 demonstrated transformation by showing that heat-killed virulent pneumococci could transfer virulence to live non-virulent bacteria. Avery et al. later identified the transforming principle as DNA.
This question belongs to: Science Biology
Question #1215
The organ that produces the enzyme renin is the:
A. Pancreas
B. Stomach
C. Liver
D. Kidney
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Correct Answer: Option D

Explanation:
Renin is released by juxtaglomerular cells of the kidney when blood pressure drops. It starts the renin-angiotensin-aldosterone system. Note: rennin (chymosin) is in the stomach for milk digestion.
This question belongs to: Science Biology
Question #1216
The disease caused by the deficiency of iodine is:
A. Anemia
B. Goiter
C. Rickets
D. Scurvy
Discuss
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Correct Answer: Option B

Explanation:
Iodine deficiency leads to insufficient thyroid hormone production, causing TSH hypersecretion and thyroid gland enlargement (goiter). Anemia is iron/B₁₂/folate deficiency, rickets vitamin D, scurvy vitamin C.
This question belongs to: Science Biology
Question #1217
The pigment that is responsible for the red color of tomatoes and watermelon is:
A. Chlorophyll
B. Beta-carotene
C. Anthocyanin
D. Lycopene
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Correct Answer: Option D

Explanation:
Lycopene is a red carotenoid pigment that accumulates in ripe tomatoes and watermelon. Beta-carotene is orange, chlorophyll green, anthocyanin purple/red in some plants.
This question belongs to: Science Biology
Question #1218
The structure that separates the right and left ventricles of the heart is the:
A. Atrium
B. Septum
C. Valve
D. Aorta
Discuss
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Correct Answer: Option B

Explanation:
The interventricular septum is a thick muscular wall that divides the two ventricles, preventing mixing of oxygenated and deoxygenated blood. Valves prevent backflow, atria are upper chambers.
This question belongs to: Science Biology
Question #1219
The enzyme that converts fibrinogen to fibrin during blood clotting is:
A. Thrombin
B. Fibrinogen
C. Prothrombin
D. Plasmin
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Correct Answer: Option A

Explanation:
Thrombin, a serine protease, converts soluble fibrinogen into insoluble fibrin, forming a blood clot. Prothrombin is its precursor, plasmin breaks down clots.
This question belongs to: Science Biology
Question #1220
The scientist who discovered the bacterium that causes plague (Yersinia pestis) was:
A. Robert Koch
B. Alexandre Yersin
C. Edward Jenner
D. Louis Pasteur
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Correct Answer: Option B

Explanation:
Alexandre Yersin, a Swiss-French bacteriologist, discovered Yersinia pestis in 1894 during the Hong Kong plague epidemic. Koch discovered TB, Pasteur developed vaccines.
This question belongs to: Science Biology

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