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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Question #601
Who was the first scientist to view live sperm cells and bacteria under a microscope?
A. Robert Hooke
B. Louis Pasteur
C. Antonie van Leeuwenhoek
D. Robert Koch
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Correct Answer: Option C

Explanation:
Antonie van Leeuwenhoek, using his hand-crafted single-lens microscopes, was the first to observe and describe living sperm cells, bacteria, protozoa, and red blood cells in the 1670s. Hooke saw dead cork cells, Pasteur and Koch later advanced microbiology with germ theory and pure culture techniques.
This question belongs to: Science Biology
Question #602
Assertion (A): The cell membrane is described by the fluid mosaic model. Reason (R): The phospholipid bilayer is fluid, and proteins are embedded like a mosaic.
A. A is true, but R is false.
B. Both A and R are true, and R is the correct explanation of A.
C. Both A and R are true, but R is not the correct explanation of A.
D. A is false, but R is true.
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Correct Answer: Option B

Explanation:
The fluid mosaic model, proposed by Singer and Nicolson in 1972, accurately describes the plasma membrane. The phospholipid bilayer has a fluid consistency, allowing lateral movement of lipids and proteins. Proteins float within or on this bilayer, forming a mosaic pattern. Thus, the reason correctly explains the assertion.
This question belongs to: Science Biology
Question #603
Which of the following is NOT a type of plastid?
A. Chromoplast
B. Peroxisome
C. Leucoplast
D. Chloroplast
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Correct Answer: Option B

Explanation:
Peroxisomes are single-membrane organelles involved in oxidative reactions, not plastids. Plastids (chloroplasts, chromoplasts, leucoplasts) are double-membrane organelles found in plants and algae, involved in photosynthesis, storage, and pigmentation. Chloroplasts contain chlorophyll, chromoplasts carotenoids, leucoplasts are colorless storage plastids.
This question belongs to: Science Biology
Question #604
In human blood, the universal recipient blood group is:
A. B positive
B. AB positive
C. A negative
D. O negative
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Correct Answer: Option B

Explanation:
AB positive blood has both A and B antigens and the Rh antigen, so it lacks antibodies against A, B, or Rh. Hence, individuals with AB+ can receive red blood cells from any donor without agglutination. O negative is the universal donor. Compatibility depends on antigens on donor RBCs and antibodies in recipient plasma.
This question belongs to: Science Biology
Question #605
The condition caused by excessive secretion of growth hormone in adults is:
A. Cretinism
B. Dwarfism
C. Acromegaly
D. Gigantism
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Correct Answer: Option C

Explanation:
Acromegaly results from overproduction of growth hormone after the epiphyseal plates have fused, causing enlargement of hands, feet, jaw, and facial features. Gigantism occurs when excess GH is produced during childhood, leading to tall stature. Dwarfism is GH deficiency, cretinism is congenital hypothyroidism.
This question belongs to: Science Biology
Question #606
The process by which bacteria take up free DNA from the environment is:
A. Conjugation
B. Transformation
C. Transduction
D. Binary fission
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Correct Answer: Option B

Explanation:
Transformation involves the uptake and incorporation of naked DNA fragments from the surrounding medium by competent bacteria. Conjugation requires cell-to-cell contact via a pilus, transduction is gene transfer by bacteriophages, binary fission is asexual reproduction. Griffith's experiment demonstrated transformation.
This question belongs to: Science Biology
Question #607
Which of the following plant hormones is a gas?
A. Ethylene
B. Abscisic acid
C. Auxin
D. Cytokinin
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Correct Answer: Option A

Explanation:
Ethylene (C₂H₄) is the only gaseous plant hormone, known for promoting fruit ripening, leaf abscission, and senescence. Auxin, cytokinin, gibberellin, and abscisic acid are non-gaseous compounds. Ethylene is used commercially to ripen fruits like bananas and tomatoes.
This question belongs to: Science Biology
Question #608
The microorganism that causes food poisoning from improperly canned foods is:
A. Escherichia coli
B. Clostridium botulinum
C. Salmonella enterica
D. Staphylococcus aureus
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Correct Answer: Option B

Explanation:
Clostridium botulinum, an anaerobic spore-forming bacterium, produces a potent neurotoxin causing botulism, often from improperly canned low-acid foods. Salmonella and E. coli cause gastroenteritis from contaminated food/water, Staphylococcus aureus produces enterotoxins causing acute vomiting. Botulism can be fatal without antitoxin.
This question belongs to: Science Biology
Question #609
The pigment that gives red color to tomatoes is:
A. Lycopene
B. Chlorophyll
C. Beta-carotene
D. Xanthophyll
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Correct Answer: Option A

Explanation:
Lycopene is a red carotenoid pigment found in tomatoes, watermelon, and pink grapefruit. It is an antioxidant and not a precursor of vitamin A. Beta-carotene is orange and a provitamin A. Chlorophyll is green, xanthophyll yellow. Lycopene is concentrated during ripening as chlorophyll degrades.
This question belongs to: Science Biology
Question #610
The organ that produces insulin and glucagon is the:
A. Pancreas
B. Spleen
C. Kidney
D. Liver
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Correct Answer: Option A

Explanation:
The endocrine islets of Langerhans in the pancreas contain alpha cells that secrete glucagon and beta cells that secrete insulin, which regulate blood glucose. The liver stores and releases glucose, the spleen filters blood, the kidneys excrete waste. The pancreas also has exocrine functions secreting digestive enzymes.
This question belongs to: Science Biology
Question #611
The enzyme that converts glucose into ethanol in yeast is:
A. Lactase
B. Zymase
C. Maltase
D. Invertase
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Correct Answer: Option B

Explanation:
Zymase is the enzyme complex in yeast that catalyzes alcoholic fermentation, converting pyruvate to ethanol and CO₂. Invertase hydrolyzes sucrose, lactase breaks lactose, maltase breaks maltose. Zymase activity is exploited in baking and brewing industries.
This question belongs to: Science Biology
Question #612
The largest and most diverse phylum in the animal kingdom is:
A. Arthropoda
B. Mollusca
C. Annelida
D. Chordata
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Correct Answer: Option A

Explanation:
Arthropoda is the largest phylum, with over a million described species, including insects, arachnids, crustaceans, and myriapods. They are characterized by jointed appendages, chitinous exoskeleton, and segmented bodies. Insects alone represent the majority of animal species. Chordata is comparatively smaller.
This question belongs to: Science Biology
Question #613
The specific part of the respiratory system where gas exchange occurs is the:
A. Bronchi
B. Trachea
C. Alveoli
D. Nasal cavity
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Correct Answer: Option C

Explanation:
Alveoli are tiny, thin-walled air sacs surrounded by pulmonary capillaries. Oxygen diffuses across the alveolar and capillary walls into the blood, while CO₂ diffuses out. The trachea, bronchi, and nasal cavity are air passages that do not participate directly in gas exchange.
This question belongs to: Science Biology
Question #614
The enzyme that breaks down fats in the digestive system is:
A. Pepsin
B. Amylase
C. Sucrase
D. Lipase
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Correct Answer: Option D

Explanation:
Lipase, primarily pancreatic lipase, hydrolyzes triglycerides into monoglycerides and free fatty acids in the small intestine, aided by bile salts that emulsify fats. Amylase digests starch, pepsin proteins, sucrase sucrose. Lipases are also secreted by lingual and gastric glands but pancreatic lipase is the main.
This question belongs to: Science Biology
Question #615
The bone that protects the brain is the:
A. Pelvis
B. Sternum
C. Vertebra
D. Cranium
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Correct Answer: Option D

Explanation:
The cranium (skull) is composed of several bones fused together, encasing and protecting the brain. Vertebrae protect the spinal cord, sternum protects the heart and lungs anteriorly, pelvis supports abdominal organs and connects to legs. The cranium also provides attachment for muscles.
This question belongs to: Science Biology
Question #616
The condition caused by vitamin D deficiency in adults is:
A. Kwashiorkor
B. Osteomalacia
C. Rickets
D. Scurvy
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Correct Answer: Option B

Explanation:
Osteomalacia is softening of bones in adults due to vitamin D deficiency, leading to bone pain and muscle weakness. Rickets is the childhood equivalent, affecting growth plates. Scurvy is vitamin C deficiency, kwashiorkor is protein deficiency. Vitamin D is essential for calcium absorption and bone mineralization.
This question belongs to: Science Biology
Question #617
The term for a sequence of three nucleotides on tRNA that is complementary to an mRNA codon is:
A. Anticodon
B. Exon
C. Codon
D. Promoter
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Correct Answer: Option A

Explanation:
The anticodon is a triplet of nucleotides on the tRNA molecule that base-pairs with the complementary codon on mRNA during translation, ensuring correct amino acid incorporation. Codons are on mRNA, promoters are DNA sequences for transcription initiation, exons are coding regions in eukaryotic genes.
This question belongs to: Science Biology
Question #618
The green revolution in India was primarily based on the introduction of:
A. High-yielding varieties of wheat and rice
B. Organic farming
C. Genetically modified crops
D. Aquaculture
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Correct Answer: Option A

Explanation:
The Green Revolution (1960s-70s) involved adopting high-yielding varieties (HYVs) of wheat and rice, along with chemical fertilizers, pesticides, and irrigation, leading to dramatic increases in food grain production in India. Norman Borlaug was instrumental. GM crops came later. Organic farming is traditional and low-input.
This question belongs to: Science Biology
Question #619
The element that is essential for the synthesis of auxin in plants is:
A. Manganese
B. Copper
C. Zinc
D. Iron
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Correct Answer: Option C

Explanation:
Zinc is a micronutrient that acts as a cofactor for tryptophan synthetase, an enzyme involved in the biosynthesis of the auxin indole-3-acetic acid (IAA) from tryptophan. Zinc deficiency causes stunted growth and 'little leaf' disease. Iron is for chlorophyll synthesis, copper for enzymes, manganese for photosystem II.
This question belongs to: Science Biology
Question #620
The movement of molecules against the concentration gradient with the use of ATP is:
A. Active transport
B. Osmosis
C. Diffusion
D. Facilitated diffusion
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Correct Answer: Option A

Explanation:
Active transport uses energy (usually ATP) to pump molecules or ions across a membrane against their electrochemical gradient, e.g., Na⁺/K⁺ pump. Diffusion, osmosis, and facilitated diffusion are passive processes that move substances down their gradient without energy expenditure.
This question belongs to: Science Biology

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