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 98 of 103
Question #1941
The 'master gland' of the human body is the:
A. Thyroid
B. Pituitary
C. Hypothalamus
D. Adrenal
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Correct Answer: Option B

Explanation:
The pituitary gland controls many other endocrine glands via tropic hormones (TSH, ACTH, FSH, LH). It is regulated by the hypothalamus. Thus, it is often called the master gland.
This question belongs to: Science Biology
Question #1942
Thyroxine hormone is produced by the:
A. Pituitary gland
B. Thyroid gland
C. Parathyroid gland
D. Adrenal gland
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Correct Answer: Option B

Explanation:
Thyroxine (T₄) and triiodothyronine (T₃) are synthesized by thyroid follicular cells. They regulate basal metabolic rate, growth, and development. Iodine is essential for their synthesis.
This question belongs to: Science Biology
Question #1943
Which hormone regulates the blood calcium level by lowering it?
A. Thyroxine
B. Parathyroid hormone
C. Insulin
D. Calcitonin
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Correct Answer: Option D

Explanation:
Calcitonin, secreted by parafollicular (C) cells of the thyroid, decreases blood calcium by inhibiting osteoclasts and promoting calcium deposition in bones. Parathyroid hormone (PTH) raises calcium.
This question belongs to: Science Biology
Question #1944
Growth hormone is secreted by which part of the pituitary?
A. Intermediate lobe
B. Posterior lobe
C. Anterior lobe
D. Hypothalamus
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Correct Answer: Option C

Explanation:
Growth hormone (somatotropin) is produced by the anterior pituitary. It promotes growth of bones, muscles, and other tissues. Deficiency causes dwarfism; excess causes gigantism or acromegaly.
This question belongs to: Science Biology
Question #1945
Which hormone is released during breastfeeding to eject milk?
A. Prolactin
B. Oxytocin
C. Estrogen
D. Progesterone
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Correct Answer: Option B

Explanation:
Oxytocin, released from the posterior pituitary, causes contraction of myoepithelial cells in mammary alveoli, forcing milk into ducts (let-down reflex). Prolactin stimulates milk synthesis.
This question belongs to: Science Biology
Question #1946
Which gland produces the hormone melatonin?
A. Adrenal gland
B. Thymus gland
C. Pineal gland
D. Thyroid gland
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Correct Answer: Option C

Explanation:
The pineal gland, located in the brain, secretes melatonin, which regulates circadian rhythms and the sleep-wake cycle. Its secretion increases in darkness.
This question belongs to: Science Biology
Question #1947
The hormone responsible for the male secondary sexual characteristics is:
A. Prolactin
B. Estrogen
C. Progesterone
D. Testosterone
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Correct Answer: Option D

Explanation:
Testosterone, produced by Leydig cells in the testes, promotes development of male characteristics like facial hair, deepening of voice, and muscle growth. It also regulates spermatogenesis.
This question belongs to: Science Biology
Question #1948
Which of the following is a steroid hormone?
A. Insulin
B. Adrenaline
C. Cortisol
D. Growth hormone
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Correct Answer: Option C

Explanation:
Cortisol (a glucocorticoid) from the adrenal cortex is a steroid hormone derived from cholesterol. Insulin and growth hormone are peptides, adrenaline is a catecholamine (amino acid derivative).
This question belongs to: Science Biology
Question #1949
The pacemaker of the heart is the:
A. Purkinje fibers
B. Sinoatrial node
C. Bundle of His
D. Atrioventricular node
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Correct Answer: Option B

Explanation:
The SA node, located in the right atrium, spontaneously generates electrical impulses, setting the heart rate. It is the natural pacemaker. The AV node delays the impulse before it reaches the ventricles.
This question belongs to: Science Biology
Question #1950
Which chamber of the heart pumps oxygenated blood to the entire body?
A. Left ventricle
B. Right ventricle
C. Left atrium
D. Right atrium
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Correct Answer: Option A

Explanation:
The left ventricle pumps blood into the aorta and to the systemic circulation. Its wall is the thickest because it must generate high pressure.
This question belongs to: Science Biology
Question #1951
Which blood vessels have valves to prevent backflow?
A. Arterioles
B. Capillaries
C. Veins
D. Arteries
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Correct Answer: Option C

Explanation:
Veins carry blood back to the heart under low pressure and have one-way valves that prevent backflow. Skeletal muscle contractions also assist venous return.
This question belongs to: Science Biology
Question #1952
The normal systolic blood pressure of a healthy adult is about:
A. 80 mmHg
B. 200 mmHg
C. 120 mmHg
D. 160 mmHg
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Correct Answer: Option C

Explanation:
Normal blood pressure is around 120/80 mmHg (systolic/diastolic). Systolic pressure is during ventricular contraction; diastolic during relaxation. Hypertension is >140/90 mmHg.
This question belongs to: Science Biology
Question #1953
The iron-containing protein in RBCs that transports oxygen is:
A. Myoglobin
B. Hemoglobin
C. Collagen
D. Albumin
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Correct Answer: Option B

Explanation:
Hemoglobin in red blood cells binds oxygen in the lungs and releases it in tissues. Each hemoglobin molecule can bind four O₂ molecules. It also carries some CO₂.
This question belongs to: Science Biology
Question #1954
The normal life span of human red blood cells is about:
A. 365 days
B. 10 days
C. 30 days
D. 120 days
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Correct Answer: Option D

Explanation:
Mature human RBCs have a lifespan of approximately 120 days, after which they are phagocytosed by macrophages in the spleen, liver, and bone marrow.
This question belongs to: Science Biology
Question #1955
Blood group AB is considered the universal recipient because:
A. It has both A and B antigens and no antibodies.
B. It has both A and B antibodies.
C. It has no A or B antigens.
D. It has no Rh antigen.
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Correct Answer: Option A

Explanation:
AB positive blood has A and B antigens on RBCs and lacks anti-A and anti-B antibodies, so it can receive blood from any ABO group without agglutination.
This question belongs to: Science Biology
Question #1956
The respiratory pigment in earthworm is:
A. Hemoglobin
B. Myoglobin
C. Hemocyanin
D. Hemoerythrin
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Correct Answer: Option A

Explanation:
Earthworms have hemoglobin dissolved in their blood plasma (not in cells) for oxygen transport. Hemocyanin is in mollusks and arthropods, hemerythrin in some marine worms.
This question belongs to: Science Biology
Question #1957
The primary muscle of breathing is the:
A. Diaphragm
B. Pectoral muscles
C. Abdominal muscles
D. Intercostal muscles
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Correct Answer: Option A

Explanation:
The diaphragm is a dome-shaped skeletal muscle that contracts during inspiration, flattening and increasing thoracic volume. The external intercostal muscles assist.
This question belongs to: Science Biology
Question #1958
The site of gas exchange in the human lungs is:
A. Bronchi
B. Trachea
C. Bronchioles
D. Alveoli
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Correct Answer: Option D

Explanation:
Alveoli are tiny thin-walled air sacs surrounded by pulmonary capillaries. Oxygen diffuses into blood, and carbon dioxide diffuses out.
This question belongs to: Science Biology
Question #1959
The functional unit of the kidney is:
A. Alveolus
B. Nephron
C. Neuron
D. Villus
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Correct Answer: Option B

Explanation:
Each kidney contains about one million nephrons, each consisting of a renal corpuscle (glomerulus + Bowman's capsule) and tubules (PCT, loop of Henle, DCT).
This question belongs to: Science Biology
Question #1960
Glucose is primarily reabsorbed in which part of the nephron?
A. Distal convoluted tubule
B. Collecting duct
C. Proximal convoluted tubule
D. Loop of Henle
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Correct Answer: Option C

Explanation:
The proximal convoluted tubule reabsorbs nearly 100% of filtered glucose, amino acids, and vitamins via active and secondary active transport.
This question belongs to: Science Biology

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