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 97 of 103
Question #1921
Consider statements about human immunity: 1. Innate immunity is present from birth. 2. Acquired immunity develops after exposure. 3. Vaccines provide natural immunity. Which are correct?
A. 1 and 2 only
B. 2 and 3 only
C. 1 and 3 only
D. 1, 2 and 3
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Correct Answer: Option A

Explanation:
Innate (natural) immunity is the non-specific defense mechanism present from birth, including physical barriers like skin and chemical barriers like stomach acid. Acquired (adaptive) immunity is highly specific and develops after the body is exposed to a specific pathogen or antigen, involving the production of antibodies and memory cells. Vaccines provide artificial immunity (specifically, artificial active immunity), not natural immunity, which is acquired through actual infection or from mother to child. Thus, statements 1 and 2 are correct.
This question belongs to: Science Biology
Question #1922
Which of the following vitamins is also known as 'retinol'?
A. Vitamin C
B. Vitamin D
C. Vitamin B₁
D. Vitamin A
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Correct Answer: Option D

Explanation:
Vitamin A is chemically known as retinol. It is essential for vision, immune function, and epithelial maintenance. Vitamin B₁ is thiamine, C is ascorbic acid, D is calciferol. Deficiency of vitamin A causes night blindness and xerophthalmia.
This question belongs to: Science Biology
Question #1923
The deficiency of vitamin B₁ (thiamine) leads to:
A. Beriberi
B. Pellagra
C. Rickets
D. Scurvy
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Correct Answer: Option A

Explanation:
Beriberi is a disease affecting the nervous and cardiovascular systems due to lack of thiamine (B₁). Scurvy is vitamin C deficiency, pellagra is niacin (B₃), rickets is vitamin D. Thiamine is a coenzyme in carbohydrate metabolism.
This question belongs to: Science Biology
Question #1924
Which vitamin is essential for the synthesis of prothrombin and blood clotting?
A. Vitamin E
B. Vitamin C
C. Vitamin K
D. Vitamin A
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Correct Answer: Option C

Explanation:
Vitamin K is required for the gamma-carboxylation of clotting factors II, VII, IX, and X, including prothrombin. Deficiency leads to prolonged clotting time and hemorrhagic disorders.
This question belongs to: Science Biology
Question #1925
Ascorbic acid is the chemical name of:
A. Vitamin B₁₂
B. Vitamin C
C. Vitamin B₂
D. Vitamin D
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Correct Answer: Option B

Explanation:
Vitamin C is chemically L-ascorbic acid. It is water-soluble, an antioxidant, and required for collagen synthesis. Deficiency causes scurvy. It is found in citrus fruits, amla, and green vegetables.
This question belongs to: Science Biology
Question #1926
Which vitamin can be synthesized by the human skin on exposure to sunlight?
A. Vitamin A
B. Vitamin D
C. Vitamin C
D. Vitamin B₆
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Correct Answer: Option B

Explanation:
Vitamin D (cholecalciferol) is synthesized in the skin from 7-dehydrocholesterol under UV-B radiation. It then undergoes activation in the liver and kidneys. It regulates calcium and phosphate metabolism.
This question belongs to: Science Biology
Question #1927
Tocopherol is the chemical name of which vitamin?
A. Vitamin A
B. Vitamin B₁₂
C. Vitamin K
D. Vitamin E
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Correct Answer: Option D

Explanation:
Vitamin E is a group of tocopherols and tocotrienols, acting as fat-soluble antioxidants. They protect cell membranes from oxidative damage. Deficiency is rare but can cause hemolytic anemia and neurological problems.
This question belongs to: Science Biology
Question #1928
The deficiency disease 'pellagra' is caused by lack of:
A. Niacin
B. Riboflavin
C. Thiamine
D. Biotin
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Correct Answer: Option A

Explanation:
Pellagra, characterized by dermatitis, diarrhea, and dementia (3 Ds), is due to deficiency of niacin (vitamin B₃) or its precursor tryptophan. Niacin is part of NAD and NADP coenzymes.
This question belongs to: Science Biology
Question #1929
Riboflavin is also known as:
A. Vitamin B₂
B. Vitamin B₁₂
C. Vitamin B₁
D. Vitamin B₆
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Correct Answer: Option A

Explanation:
Vitamin B₂ is riboflavin, a component of coenzymes FAD and FMN involved in redox reactions. Deficiency causes angular stomatitis, cheilosis, and glossitis. It is water-soluble.
This question belongs to: Science Biology
Question #1930
Pyridoxine is the chemical name of:
A. Vitamin B₃
B. Vitamin B₆
C. Vitamin B₂
D. Vitamin B₁
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Correct Answer: Option B

Explanation:
Vitamin B₆ exists in three forms: pyridoxine, pyridoxal, and pyridoxamine. Its active form, pyridoxal phosphate (PLP), is a coenzyme in amino acid metabolism and neurotransmitter synthesis. Deficiency can cause peripheral neuropathy and anemia.
This question belongs to: Science Biology
Question #1931
Which vitamin is also called 'cobalamin'?
A. Vitamin B₁₂
B. Vitamin B₆
C. Vitamin B₉
D. Vitamin B₁
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Correct Answer: Option A

Explanation:
Vitamin B₁₂ contains cobalt, hence the name cobalamin. It is involved in DNA synthesis, red blood cell maturation, and nervous system maintenance. Deficiency leads to pernicious anemia and neurological disorders.
This question belongs to: Science Biology
Question #1932
Folic acid (folate) deficiency during pregnancy increases the risk of:
A. Neural tube defects
B. Scurvy
C. Night blindness
D. Rickets
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Correct Answer: Option A

Explanation:
Folate (vitamin B₉) is crucial for DNA synthesis and cell division. Inadequate folate early in pregnancy can cause neural tube defects like spina bifida in the fetus. Supplementation is recommended.
This question belongs to: Science Biology
Question #1933
Biotin is a vitamin that acts as a coenzyme for:
A. Decarboxylation reactions
B. Carboxylation reactions
C. Transamination reactions
D. Oxidation reactions
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Correct Answer: Option B

Explanation:
Biotin (vitamin B₇) is a coenzyme for carboxylases, e.g., pyruvate carboxylase, acetyl-CoA carboxylase. It is involved in gluconeogenesis and fatty acid synthesis. Deficiency is rare but can occur with raw egg white consumption.
This question belongs to: Science Biology
Question #1934
Which mineral is required for the formation of hemoglobin?
A. Calcium
B. Iron
C. Zinc
D. Iodine
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Correct Answer: Option B

Explanation:
Iron (Fe²⁺) is the central atom of heme in hemoglobin and myoglobin, essential for oxygen transport. Deficiency leads to microcytic hypochromic anemia. Good sources: liver, meat, leafy greens.
This question belongs to: Science Biology
Question #1935
Iodine deficiency primarily affects the function of which gland?
A. Thyroid
B. Adrenal
C. Pancreas
D. Pituitary
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Correct Answer: Option A

Explanation:
Iodine is essential for the synthesis of thyroid hormones T₃ and T₄. Deficiency causes hypothyroidism and goiter (enlarged thyroid gland). Iodized salt is a preventive measure.
This question belongs to: Science Biology
Question #1936
Calcium absorption from the intestine is promoted by:
A. Vitamin D
B. Vitamin C
C. Vitamin B₁₂
D. Vitamin A
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Correct Answer: Option A

Explanation:
Active vitamin D (calcitriol) induces synthesis of calcium-binding proteins in the intestinal mucosa, enhancing calcium absorption. Calcium is vital for bones, teeth, blood clotting, and nerve-muscle function.
This question belongs to: Science Biology
Question #1937
Which of the following is a trace element?
A. Sodium
B. Zinc
C. Phosphorus
D. Potassium
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Correct Answer: Option B

Explanation:
Zinc is a micronutrient (trace mineral) required in small amounts for enzyme function, immune response, and wound healing. Sodium, potassium, and phosphorus are macrominerals.
This question belongs to: Science Biology
Question #1938
The disease 'anemia' is most commonly caused by deficiency of:
A. Magnesium
B. Calcium
C. Iron
D. Iodine
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Correct Answer: Option C

Explanation:
Iron-deficiency anemia is the most prevalent nutritional deficiency worldwide, characterized by fatigue, pallor, and reduced oxygen-carrying capacity. It is treated with iron supplementation and dietary changes.
This question belongs to: Science Biology
Question #1939
Which mineral is the main component of bones and teeth along with calcium?
A. Sodium
B. Fluorine
C. Phosphorus
D. Selenium
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Correct Answer: Option C

Explanation:
Calcium phosphate (hydroxyapatite) gives bones and teeth their hardness. Phosphorus is also a component of ATP, DNA, and cell membranes. Dairy products, meat, and nuts are good sources.
This question belongs to: Science Biology
Question #1940
The hormone insulin is produced by which cells of the pancreas?
A. Delta cells
B. Beta cells
C. Acinar cells
D. Alpha cells
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Correct Answer: Option B

Explanation:
Beta cells of the islets of Langerhans secrete insulin, which lowers blood glucose. Alpha cells secrete glucagon (raises glucose), delta cells somatostatin, and acinar cells produce digestive enzymes.
This question belongs to: Science Biology

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