Biology MCQs

Question #541

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The condition in which the blood has a lower than normal number of red blood cells or hemoglobin is:

A. Leukemia

B. Anemia

C. Polycythemia

D. Thalassemia

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Correct Answer: Option B

Explanation:
Anemia is a deficiency in RBCs or hemoglobin, reducing oxygen-carrying capacity. Causes: iron deficiency, vitamin B₁₂/folate deficiency, blood loss, hemolysis. Polycythemia is excess RBCs, leukemia is cancer of WBCs, thalassemia is a genetic hemoglobin disorder leading to anemia. Anemia causes fatigue and pallor.

This question belongs to: Science Biology

Question #542

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The molecule that acts as the universal energy carrier in cells is:

A. NADPH

B. Acetyl CoA

C. ATP

D. Glucose

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Correct Answer: Option C

Explanation:
ATP (adenosine triphosphate) is the immediate energy currency for cellular processes. Hydrolysis of its high-energy phosphate bonds releases energy. Glucose and acetyl CoA are fuels, NADPH is an electron donor for biosynthesis. ATP is generated by substrate-level phosphorylation and oxidative phosphorylation.

This question belongs to: Science Biology

Question #543

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The valve that prevents backflow from the right ventricle into the right atrium is the:

A. Bicuspid valve

B. Tricuspid valve

C. Aortic valve

D. Pulmonary valve

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Correct Answer: Option B

Explanation:
The tricuspid valve (right atrioventricular valve) has three cusps and closes during ventricular systole to prevent regurgitation into the right atrium. The bicuspid (mitral) is on the left side. Aortic and pulmonary valves are semilunar valves at the ventricular outlets.

This question belongs to: Science Biology

Question #544

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The part of the brain that acts as a relay station for sensory information is the:

A. Thalamus

B. Medulla

C. Cerebellum

D. Hypothalamus

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Correct Answer: Option A

Explanation:
The thalamus, a paired structure in the diencephalon, processes and relays sensory information (except olfaction) to the cerebral cortex. It also regulates consciousness and alertness. The cerebellum coordinates movement, hypothalamus maintains homeostasis, medulla controls vital reflexes.

This question belongs to: Science Biology

Question #545

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The process of new blood vessel formation is called:

A. Hematopoiesis

B. Angiogenesis

C. Vasodilation

D. Vasoconstriction

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Correct Answer: Option B

Explanation:
Angiogenesis is the growth of new blood vessels from pre-existing ones, important in development, wound healing, and tumor growth. Vasodilation is widening, vasoconstriction narrowing of vessels. Hematopoiesis is blood cell formation. Inhibiting angiogenesis is a cancer therapy strategy.

This question belongs to: Science Biology

Question #546

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The genetic makeup of an organism is its:

A. Phenotype

B. Allele

C. Karyotype

D. Genotype

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Correct Answer: Option D

Explanation:
Genotype refers to the specific set of genes (allelic constitution) of an individual, e.g., TT, Tt, or tt for a trait. Phenotype is the observable characteristic, karyotype is the chromosome complement, allele is a variant form of a gene. The genotype determines the potential phenotype.

This question belongs to: Science Biology

Question #547

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The end product of glycolysis under anaerobic conditions in muscles is:

A. Ethanol

B. Lactic acid

C. Carbon dioxide

D. Acetyl CoA

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Correct Answer: Option B

Explanation:
When oxygen is limiting, pyruvate from glycolysis is reduced to lactic acid (lactate) by lactate dehydrogenase, regenerating NAD⁺ to allow glycolysis to continue. In yeast, pyruvate is converted to ethanol and CO₂ (alcoholic fermentation). Muscle cells lack alcohol dehydrogenase.

This question belongs to: Science Biology

Question #548

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The pigment that is the primary electron donor in photosystem I is:

A. P680

B. P700

C. Chlorophyll b

D. Carotenoid

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Correct Answer: Option B

Explanation:
P700 is the reaction center chlorophyll a of photosystem I, absorbing light at 700 nm. It donates electrons to ferredoxin. P680 is the reaction center of PSII. Chlorophyll b and carotenoids are accessory pigments. The two photosystems work in series to transfer electrons from water to NADP⁺.

This question belongs to: Science Biology

Question #549

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The structure that provides buoyancy to aquatic plants is:

A. Aerenchyma

B. Sclerenchyma

C. Collenchyma

D. Xylem

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Correct Answer: Option A

Explanation:
Aerenchyma is a specialized parenchyma tissue with large intercellular air spaces, providing buoyancy and facilitating gas exchange in aquatic plants. It also helps in oxygen transport to submerged roots. Sclerenchyma is supportive, collenchyma flexible support, xylem water-conducting.

This question belongs to: Science Biology

Question #550

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Which of the following diseases is caused by a prion?

A. Creutzfeldt-Jakob disease

B. Rabies

C. Influenza

D. Polio

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Correct Answer: Option A

Explanation:
Creutzfeldt-Jakob disease (CJD) is a rare, fatal brain disorder caused by misfolded prion proteins (PrP^Sc), which are infectious protein particles lacking nucleic acid. Rabies, polio, and influenza are caused by viruses. Prions cause spongiform encephalopathies like mad cow disease (BSE).

This question belongs to: Science Biology

Question #551

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The female sex hormone produced by the corpus luteum is:

A. Estrogen

B. Progesterone

C. Prolactin

D. Testosterone

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Correct Answer: Option B

Explanation:
The corpus luteum, formed after ovulation, secretes progesterone (and some estrogen) to maintain the uterine lining for pregnancy. If no fertilization, it degenerates, causing menstruation. Estrogen is also produced by growing follicles, testosterone by Leydig cells, prolactin by anterior pituitary.

This question belongs to: Science Biology

Question #552

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The disease characterized by the inflammation of the liver caused by a virus is:

A. Pancreatitis

B. Nephritis

C. Hepatitis

D. Cirrhosis

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Correct Answer: Option C

Explanation:
Hepatitis (A, B, C, etc.) is liver inflammation, often viral. Symptoms include jaundice, fatigue, and liver enzyme elevation. Cirrhosis is liver scarring, pancreatitis is pancreatic inflammation, nephritis is kidney inflammation. Hepatitis B and C can become chronic and lead to liver cancer.

This question belongs to: Science Biology

Question #553

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The process by which plants prepare their own food using light energy is known as:

A. Photosynthesis

B. Transpiration

C. Chemosynthesis

D. Respiration

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Correct Answer: Option A

Explanation:
Photosynthesis converts CO₂ and H₂O into glucose and oxygen using light energy, catalyzed by chlorophyll in chloroplasts. This process sustains nearly all life, providing food and oxygen. Respiration releases energy from glucose, chemosynthesis uses chemical energy, transpiration is water loss.

This question belongs to: Science Biology

Question #554

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The scientist who demonstrated that DNA replication is semi-conservative was:

A. Meselson and Stahl

B. Hershey and Chase

C. Chargaff

D. Watson and Crick

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Correct Answer: Option A

Explanation:
Matthew Meselson and Franklin Stahl, in 1958, used density gradient centrifugation of E. coli grown in N¹⁵ medium to prove that DNA replication is semi-conservative: each new DNA molecule consists of one old and one new strand. Watson and Crick proposed the double helix, Hershey-Chase confirmed DNA as genetic material, Chargaff formulated base pair rules.

This question belongs to: Science Biology

Question #555

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The muscular tube that connects the pharynx to the stomach is the:

A. Trachea

B. Larynx

C. Bronchus

D. Esophagus

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Correct Answer: Option D

Explanation:
The esophagus is a muscular tube (about 25 cm) that propels swallowed food from the pharynx to the stomach via peristalsis. The trachea is the windpipe (air), larynx is the voice box, bronchus is a lung airway. The esophageal sphincters prevent reflux.

This question belongs to: Science Biology

Question #556

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The structure that regulates the entry of light into the eye is the:

A. Retina

B. Pupil

C. Cornea

D. Lens

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Correct Answer: Option B

Explanation:
The pupil is the opening in the center of the iris whose size is adjusted by the iris muscles to control the amount of light entering the eye. The cornea and lens focus light, the retina senses it. In bright light, the pupil constricts; in dim light, it dilates.

This question belongs to: Science Biology

Question #557

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The type of tissue that covers body surfaces and lines cavities is:

A. Epithelial tissue

B. Muscle tissue

C. Nervous tissue

D. Connective tissue

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Correct Answer: Option A

Explanation:
Epithelial tissue forms sheets covering external surfaces (skin) and lining internal organs and cavities. It functions in protection, absorption, secretion, and sensation. Connective tissue supports and binds, muscle contracts, nervous transmits impulses. Epithelial cells are tightly packed with little extracellular matrix.

This question belongs to: Science Biology

Question #558

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The vitamin that is synthesized by gut bacteria in the human intestine is:

A. Vitamin C

B. Vitamin A

C. Vitamin K

D. Vitamin D

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Correct Answer: Option C

Explanation:
Vitamin K and some B vitamins (like biotin) are synthesized by the normal microflora of the large intestine. However, the amount may be insufficient to meet total needs. Vitamin A, C, and D must be obtained from diet or sunlight. Gut bacteria contribute to vitamin K for clotting factors.

This question belongs to: Science Biology

Question #559

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The part of the seed that provides nutrition to the developing embryo is:

A. Endosperm

B. Plumule

C. Seed coat

D. Radicle

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Correct Answer: Option A

Explanation:
The endosperm is a triploid tissue in angiosperm seeds that stores starch, proteins, and lipids to nourish the embryo during germination. It is formed by double fertilization. In some seeds (e.g., legumes) the endosperm is absorbed and the cotyledons become storage organs. The seed coat protects.

This question belongs to: Science Biology

Question #560

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The gland responsible for regulating circadian rhythms is the:

A. Adrenal

B. Pineal

C. Thyroid

D. Pituitary

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Correct Answer: Option B

Explanation:
The pineal gland secretes melatonin in a daily rhythm, peaking at night, thus regulating the sleep-wake cycle and seasonal biological rhythms. The pituitary controls other glands, thyroid metabolism, adrenals stress response. Light signals from the retina influence pineal activity.

This question belongs to: Science Biology

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