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 20 of 103
Question #381
The botanical name of the potato plant is:
A. Lycopersicon esculentum
B. Capsicum annuum
C. Solanum tuberosum
D. Solanum melongena
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Correct Answer: Option C

Explanation:
Solanum tuberosum is the scientific name of potato, a member of the Solanaceae family. Solanum melongena is brinjal (eggplant), Capsicum annuum is chili, and Lycopersicon esculentum is tomato. Potato is a tuber (modified stem) rich in starch, and is one of the world's major food crops.
This question belongs to: Science Biology
Question #382
In humans, the dental formula of permanent teeth is:
A. 2122/2122
B. 2102/2102
C. 2123/2123
D. 2133/2133
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Correct Answer: Option C

Explanation:
The adult human dental formula is 2123/2123 (incisors 2, canines 1, premolars 2, molars 3) per quadrant, totaling 32 permanent teeth. Deciduous teeth formula is 2102/2102 (20 teeth). The formula represents half of the upper jaw over half of the lower jaw. Wisdom teeth (third molars) may be absent in some individuals.
This question belongs to: Science Biology
Question #383
Which plant tissue transports organic solutes from leaves to other parts?
A. Sclerenchyma
B. Phloem
C. Collenchyma
D. Xylem
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Correct Answer: Option B

Explanation:
Phloem is the vascular tissue responsible for translocation of photosynthates (mainly sucrose) from source (leaves) to sink (roots, fruits, growing regions) via sieve tubes and companion cells. Xylem transports water and minerals upward. Collenchyma and sclerenchyma are mechanical tissues. Phloem is alive at maturity.
This question belongs to: Science Biology
Question #384
The pressure that develops in roots due to active absorption of minerals and water is:
A. Turgor pressure
B. Root pressure
C. Wall pressure
D. Transpiration pull
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Correct Answer: Option B

Explanation:
Root pressure is the positive hydrostatic pressure developing in the xylem of roots due to active transport of ions into the vascular cylinder, drawing water osmotically. It can cause guttation in some plants. Transpiration pull is the main driving force for water ascent. Turgor pressure is the pressure of cell contents against the cell wall.
This question belongs to: Science Biology
Question #385
The hormone responsible for the ripening of fruits is:
A. Gibberellin
B. Ethylene
C. Auxin
D. Cytokinin
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Correct Answer: Option B

Explanation:
Ethylene is a gaseous plant hormone that promotes fruit ripening (climacteric fruits like banana, apple), leaf abscission, and senescence. Auxin, gibberellin, and cytokinin primarily promote growth. Ethylene is used commercially to ripen fruits uniformly. It also stimulates the formation of abscission layers and inhibits stem elongation.
This question belongs to: Science Biology
Question #386
The structure in the nephron that filters blood under high pressure is the:
A. Distal convoluted tubule
B. Loop of Henle
C. Collecting duct
D. Glomerulus
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Correct Answer: Option D

Explanation:
The glomerulus is a knot of capillaries enveloped by Bowman's capsule, where blood is filtered under pressure (ultrafiltration). The high hydrostatic pressure forces water, ions, glucose, and urea into the tubular system, while cells and large proteins are retained. The loop of Henle, distal tubule, and collecting duct process the filtrate.
This question belongs to: Science Biology
Question #387
Which blood vessel carries blood from the heart to the lungs?
A. Pulmonary artery
B. Pulmonary vein
C. Aorta
D. Superior vena cava
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Correct Answer: Option A

Explanation:
The pulmonary artery (trunk) exits the right ventricle and carries deoxygenated blood to the lungs for oxygenation. The pulmonary veins return oxygenated blood from the lungs to the left atrium. The aorta distributes oxygenated blood to the body, and the vena cava returns deoxygenated blood to the heart.
This question belongs to: Science Biology
Question #388
The valve between the left atrium and left ventricle is the:
A. Aortic semilunar valve
B. Tricuspid valve
C. Bicuspid (mitral) valve
D. Pulmonary semilunar valve
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Correct Answer: Option C

Explanation:
The bicuspid valve (mitral valve) has two cusps and is located between the left atrium and left ventricle, preventing backflow during ventricular systole. The tricuspid valve is on the right side. Semilunar valves are at the exits of the aorta and pulmonary artery. Mitral valve prolapse is a common condition.
This question belongs to: Science Biology
Question #389
Which component of the blood transports oxygen and carbon dioxide?
A. Thrombocytes
B. Plasma proteins
C. Erythrocytes
D. Leukocytes
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Correct Answer: Option C

Explanation:
Erythrocytes (red blood cells) contain hemoglobin, which binds oxygen (as oxyhemoglobin) and carbon dioxide (as carbaminohemoglobin). Leukocytes are immune cells, thrombocytes are platelets for clotting, and plasma proteins (e.g., albumin) maintain osmotic balance and transport some substances. The majority of CO₂ is carried as bicarbonate in plasma.
This question belongs to: Science Biology
Question #390
The enzyme secreted by the stomach that digests milk protein in infants is:
A. Pepsin
B. Rennin
C. Lipase
D. Trypsin
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Correct Answer: Option B

Explanation:
Rennin (chymosin) is a proteolytic enzyme found in the gastric juice of young mammals; it curdles milk by converting soluble caseinogen into insoluble casein, slowing its passage and allowing pepsin to digest it. Pepsin is the main adult protease, trypsin is pancreatic, and lipase digests fats. Rennin is now produced biotechnologically for cheese making.
This question belongs to: Science Biology
Question #391
The respiratory centre in the human brain is located in the:
A. Cerebellum
B. Hypothalamus
C. Medulla oblongata
D. Cerebrum
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Correct Answer: Option C

Explanation:
The medulla oblongata contains the respiratory rhythmicity centre that controls the rate and depth of breathing. The pons also has pneumotaxic and apneustic centres influencing breathing. The cerebrum can exert voluntary control, cerebellum coordinates movement, and hypothalamus regulates homeostasis.
This question belongs to: Science Biology
Question #392
The hormone that stimulates the release of glucocorticoids from the adrenal cortex is:
A. ACTH
B. TSH
C. Prolactin
D. FSH
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Correct Answer: Option A

Explanation:
Adrenocorticotropic hormone (ACTH), secreted by the anterior pituitary, stimulates the adrenal cortex to produce and release glucocorticoids like cortisol, which regulate metabolism and stress response. TSH stimulates the thyroid, FSH stimulates gonads, and prolactin stimulates milk production. ACTH is part of the HPA axis.
This question belongs to: Science Biology
Question #393
The release of which hormone is stimulated by the suckling reflex during breastfeeding?
A. Progesterone
B. Prolactin
C. Oxytocin
D. Estrogen
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Correct Answer: Option C

Explanation:
Oxytocin, produced in the hypothalamus and released from the posterior pituitary, triggers the milk let-down reflex by causing myoepithelial cells around alveoli to contract upon suckling. Prolactin stimulates milk synthesis. Estrogen and progesterone are involved in breast development during pregnancy but not the immediate ejection reflex.
This question belongs to: Science Biology
Question #394
The female reproductive structure where the embryo implants and develops is the:
A. Uterus
B. Vagina
C. Ovary
D. Fallopian tube
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Correct Answer: Option A

Explanation:
The uterus (womb) is a muscular organ where the fertilized egg implants in the thickened endometrium and develops into a fetus during pregnancy. The ovaries produce eggs, the fallopian tubes are the site of fertilization, and the vagina is the birth canal. The endometrium is shed during menstruation if no pregnancy occurs.
This question belongs to: Science Biology
Question #395
Which of the following diseases is caused by the protozoan Plasmodium vivax?
A. Giardiasis
B. Malaria
C. Sleeping sickness
D. Amoebic dysentery
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Correct Answer: Option B

Explanation:
Malaria is caused by Plasmodium species (P. vivax, P. falciparum, etc.) and transmitted by female Anopheles mosquitoes. P. vivax causes benign tertian malaria with 48-hour fever cycles. Amoebic dysentery is caused by Entamoeba histolytica, sleeping sickness by Trypanosoma, and giardiasis by Giardia. Malaria remains a major global health challenge.
This question belongs to: Science Biology
Question #396
The process of artificially introducing weakened pathogens to stimulate immunity is called:
A. Antibiosis
B. Chemotherapy
C. Immunotherapy
D. Vaccination
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Correct Answer: Option D

Explanation:
Vaccination (immunization) involves administering killed or attenuated pathogens, or their antigens, to induce active artificial immunity without causing disease. It primes the immune system to produce memory cells. Antibiosis is inhibition by another organism, immunotherapy treats disease by modulating immune response, chemotherapy uses drugs against cancer or microbes.
This question belongs to: Science Biology
Question #397
Which vitamin deficiency leads to defective blood clotting?
A. Vitamin A
B. Vitamin K
C. Vitamin B₁₂
D. Vitamin C
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Correct Answer: Option B

Explanation:
Vitamin K is essential for hepatic synthesis of clotting factors II (prothrombin), VII, IX, and X. Deficiency causes prolonged clotting time and easy bruising/bleeding. Vitamin A is for vision, B₁₂ for RBC maturation and nerve function, C for collagen synthesis. Newborns are given vitamin K to prevent hemorrhagic disease.
This question belongs to: Science Biology
Question #398
Rickets in children is characterized by:
A. Anemia and fatigue
B. Dermatitis and diarrhea
C. Bleeding gums and poor wound healing
D. Bowed legs and soft bones
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Correct Answer: Option D

Explanation:
Rickets, caused by vitamin D deficiency, results in impaired mineralization of growing bones, leading to bowed legs, knock-knees, soft skull, and delayed growth. Scurvy (vitamin C deficiency) causes bleeding gums, pellagra (niacin deficiency) causes dermatitis and diarrhea, and anemia can be due to iron or B₁₂ deficiency.
This question belongs to: Science Biology
Question #399
Which of the following is a water-soluble vitamin that acts as a coenzyme in energy metabolism?
A. Vitamin A
B. Vitamin B₁
C. Vitamin E
D. Vitamin D
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Correct Answer: Option B

Explanation:
Vitamin B₁ (thiamine) is water-soluble and functions as a coenzyme (thiamine pyrophosphate) in carbohydrate metabolism, particularly in decarboxylation reactions. Vitamins A, D, E, and K are fat-soluble. B₁ deficiency causes beriberi and Wernicke-Korsakoff syndrome. Being water-soluble, excess is excreted in urine and toxicity is rare.
This question belongs to: Science Biology
Question #400
The genetic material in a retrovirus is:
A. Double-stranded RNA
B. Double-stranded DNA
C. Single-stranded DNA
D. Single-stranded RNA
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Correct Answer: Option D

Explanation:
Retroviruses (e.g., HIV) possess two copies of single-stranded RNA and the enzyme reverse transcriptase, which transcribes the RNA into DNA upon infection. This DNA integrates into the host genome. Other viruses may have dsDNA, ssDNA, or dsRNA, but the defining feature of retroviruses is the RNA genome and reverse transcription.
This question belongs to: Science Biology

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