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 17 of 103
Question #321
The term 'antibiotic' was coined by:
A. Paul Ehrlich
B. Selman Waksman
C. Louis Pasteur
D. Alexander Fleming
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Correct Answer: Option B

Explanation:
Selman Waksman, who discovered streptomycin, coined the term 'antibiotic' in 1942 to describe chemical substances produced by microorganisms that inhibit or kill other microorganisms. Fleming discovered penicillin but did not coin the term. Pasteur developed pasteurization and rabies vaccine, Ehrlich discovered salvarsan (magic bullet) for syphilis.
This question belongs to: Science Biology
Question #322
Which of the following is a warm-blooded animal?
A. Snake
B. Fish
C. Crow
D. Frog
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Correct Answer: Option C

Explanation:
Birds and mammals are endothermic (warm-blooded), maintaining a constant internal body temperature regardless of the environment. Crow is a bird, hence warm-blooded. Fish, frog (amphibian), and snake (reptile) are ectothermic (cold-blooded), their body temperature varies with the environment. Endothermy requires high metabolic rate and insulation (feathers, fur).
This question belongs to: Science Biology
Question #323
Which of the following is NOT a nitrogenous base found in DNA?
A. Uracil
B. Guanine
C. Thymine
D. Adenine
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Correct Answer: Option A

Explanation:
DNA contains adenine, guanine, cytosine, and thymine. RNA contains uracil instead of thymine. This is one of the key differences between DNA and RNA. Uracil pairs with adenine in RNA. The base pairing in DNA is A-T and G-C. In RNA, it is A-U and G-C. Uracil lacks the methyl group present in thymine.
This question belongs to: Science Biology
Question #324
The micronutrient required for the synthesis of the plant hormone auxin is:
A. Boron
B. Iron
C. Zinc
D. Manganese
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Correct Answer: Option C

Explanation:
Zinc is an essential micronutrient for plants, involved in the synthesis of the auxin indole-3-acetic acid (IAA) via the activation of tryptophan synthetase. Zinc deficiency causes 'little leaf' and 'rosette' diseases, stunted growth, and reduced internodes. Iron is needed for chlorophyll synthesis, manganese for photosynthesis, and boron for pollen germination.
This question belongs to: Science Biology
Question #325
The phenomenon of a plant flowering in response to the length of day is called:
A. Chemotropism
B. Photoperiodism
C. Geotropism
D. Phototropism
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Correct Answer: Option B

Explanation:
Photoperiodism is the response of plants to the relative lengths of day and night, influencing flowering. Short-day plants (e.g., poinsettia) flower when day length is less than a critical period; long-day plants (e.g., spinach) flower when days are longer. Phototropism is growth towards light, geotropism to gravity, chemotropism to chemicals.
This question belongs to: Science Biology
Question #326
The metallic element essential for the formation of hemoglobin is:
A. Calcium
B. Magnesium
C. Iron
D. Potassium
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Correct Answer: Option C

Explanation:
Iron (Fe²⁺) is a central component of the heme group in hemoglobin, enabling oxygen binding. Deficiency leads to iron-deficiency anemia, characterized by fatigue, pallor, and reduced oxygen-carrying capacity. Calcium is for bones and clotting, magnesium is a cofactor and in chlorophyll, potassium is for nerve impulses. Iron is obtained from diet (meat, leafy greens).
This question belongs to: Science Biology
Question #327
Which of the following is a correct statement about the structure of a neuron?
A. The myelin sheath speeds up impulse conduction by allowing continuous conduction.
B. The axon receives impulses from other neurons.
C. Dendrites transmit impulses away from the cell body.
D. The cell body contains the nucleus and most organelles.
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Correct Answer: Option D

Explanation:
The soma (cell body) of a neuron contains the nucleus and metabolic machinery. Dendrites receive signals from other neurons and transmit them towards the soma, while the axon carries impulses away from the soma. The myelin sheath speeds up conduction by saltatory conduction (jumping between nodes), not continuous conduction.
This question belongs to: Science Biology
Question #328
The condition characterized by an enlarged thyroid gland due to dietary iodine deficiency is:
A. Simple goiter
B. Hashimoto's thyroiditis
C. Cretinism
D. Graves' disease
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Correct Answer: Option A

Explanation:
Simple (endemic) goiter is caused by iodine deficiency, leading to low production of thyroid hormones. The pituitary secretes excess TSH, stimulating the thyroid to enlarge in an attempt to produce more hormones. Cretinism is congenital hypothyroidism, Graves' disease is autoimmune hyperthyroidism, Hashimoto's is autoimmune hypothyroidism. Iodized salt prevents goiter.
This question belongs to: Science Biology
Question #329
The enzyme that catalyzes the conversion of starch into maltose is:
A. Lipase
B. Amylase
C. Protease
D. Lactase
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Correct Answer: Option B

Explanation:
Amylase (ptyalin in saliva, pancreatic amylase in intestine) hydrolyzes starch (a polysaccharide) into maltose (a disaccharide) and dextrins. Lactase breaks lactose, lipase digests lipids, protease digests proteins. Salivary amylase works at neutral pH, pancreatic amylase in the small intestine. Maltase then breaks maltose into two glucose molecules.
This question belongs to: Science Biology
Question #330
Which part of the human eye is responsible for color vision?
A. Lens
B. Cones
C. Rods
D. Cornea
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Correct Answer: Option B

Explanation:
Cones are photoreceptor cells in the retina responsible for photopic (daylight) vision and color perception. There are three types of cones sensitive to blue, green, and red wavelengths. Rods are responsible for scotopic (dim light) vision and do not detect color. The cornea and lens focus light onto the retina.
This question belongs to: Science Biology
Question #331
The process of cell death that is programmed and essential for normal development is:
A. Autolysis
B. Phagocytosis
C. Necrosis
D. Apoptosis
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Correct Answer: Option D

Explanation:
Apoptosis is a genetically controlled, energy-dependent process of programmed cell death that removes unwanted, damaged, or infected cells without causing inflammation. It is vital for development (e.g., separation of digits in fingers) and tissue homeostasis. Necrosis is traumatic cell death causing inflammation. Autolysis is self-digestion after death, phagocytosis is engulfment.
This question belongs to: Science Biology
Question #332
Which of the following pairs is a symbiotic nitrogen fixer in leguminous plants?
A. Frankia - Casuarina
B. Rhizobium - Soybean
C. Anabaena - Azolla
D. Azotobacter - Wheat
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Correct Answer: Option B

Explanation:
Rhizobium species form root nodules in leguminous plants like soybean, pea, and bean, where they fix atmospheric nitrogen symbiotically. Azotobacter is free-living, Anabaena associates with Azolla (a fern), Frankia with non-leguminous plants like Casuarina and Alnus. This symbiosis reduces the need for nitrogen fertilizers in agriculture.
This question belongs to: Science Biology
Question #333
The substance that makes the plant cell wall rigid and is a major component of wood is:
A. Pectin
B. Cellulose
C. Lignin
D. Chitin
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Correct Answer: Option C

Explanation:
Lignin is a complex organic polymer deposited in the secondary cell wall of xylem vessels and sclerenchyma fibers, providing rigidity, strength, and water resistance. It is the major non-carbohydrate component of wood. Cellulose is the main polysaccharide in the primary wall, chitin is in fungi and arthropods, pectin is in the middle lamella and primary wall.
This question belongs to: Science Biology
Question #334
Which of the following diseases is caused by a virus?
A. Malaria
B. Measles
C. Cholera
D. Anthrax
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Correct Answer: Option B

Explanation:
Measles (rubeola) is a highly contagious viral disease caused by the measles virus (a paramyxovirus), characterized by fever, cough, and a distinctive red rash. Anthrax is bacterial (Bacillus anthracis), malaria is protozoan, cholera is bacterial. Measles can be prevented by the MMR vaccine. It is a leading cause of child mortality in unvaccinated populations.
This question belongs to: Science Biology
Question #335
The vitamin that is also a hormone, synthesized by the skin upon exposure to sunlight, is:
A. Vitamin D
B. Vitamin C
C. Vitamin B₁
D. Vitamin A
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Correct Answer: Option A

Explanation:
Vitamin D (cholecalciferol) is unique as it can be synthesized in the skin from 7-dehydrocholesterol in the presence of UV-B radiation. It acts as a hormone to regulate calcium and phosphate homeostasis. It must be activated in the liver and kidneys. It is also obtained from dietary sources like fatty fish, egg yolk. Deficiency causes rickets/osteomalacia.
This question belongs to: Science Biology
Question #336
The glomerulus is a cluster of:
A. Capillaries
B. Muscle fibers
C. Neurons
D. Alveolar sacs
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Correct Answer: Option A

Explanation:
The glomerulus is a tuft of fenestrated capillaries enclosed by the Bowman's capsule in the renal corpuscle. Blood is filtered under high pressure through the capillary walls into the Bowman's space. The filtrate then passes into the nephron tubules. Glomerular filtration is the first step in urine formation.
This question belongs to: Science Biology
Question #337
Which of the following is an example of a genetically engineered insulin-producing bacterium?
A. Saccharomyces cerevisiae
B. Bacillus subtilis
C. Escherichia coli
D. Pseudomonas aeruginosa
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Correct Answer: Option C

Explanation:
Recombinant human insulin (Humulin) is produced by genetically engineered Escherichia coli (or yeast) carrying the human insulin gene. Before this, insulin from animal sources was used. The A and B chains of insulin are produced separately and then combined. This was the first genetically engineered pharmaceutical approved for human use (1982).
This question belongs to: Science Biology
Question #338
The functional connection between two bones is called a:
A. Joint
B. Cartilage
C. Tendon
D. Ligament
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Correct Answer: Option A

Explanation:
A joint (articulation) is the site where two or more bones meet, allowing movement (synovial joints) or providing stability (fibrous and cartilaginous joints). Tendons connect muscle to bone, ligaments connect bone to bone. Cartilage is a connective tissue that cushions joints. The elbow, knee, and hip are examples of synovial joints.
This question belongs to: Science Biology
Question #339
The process by which water moves from a region of higher water potential to lower water potential across a selectively permeable membrane is:
A. Diffusion
B. Active transport
C. Osmosis
D. Plasmolysis
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Correct Answer: Option C

Explanation:
Osmosis is the special case of diffusion of water across a semipermeable membrane down its concentration gradient (from high to low water potential). It does not require energy. Diffusion refers to solute movement, active transport requires energy against a gradient, and plasmolysis is the shrinking of protoplasm due to water loss.
This question belongs to: Science Biology
Question #340
The enzyme that breaks down lipids in the small intestine is primarily produced by the:
A. Stomach
B. Salivary glands
C. Liver
D. Pancreas
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Correct Answer: Option D

Explanation:
Pancreatic lipase is the major enzyme for fat digestion, secreted by the exocrine pancreas into the duodenum. It hydrolyzes triglycerides into monoglycerides and free fatty acids, aided by bile salts that emulsify fats. Gastric lipase (stomach) plays a minor role. Liver produces bile but not lipase. Salivary glands produce salivary amylase.
This question belongs to: Science Biology

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