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 33 of 103
Question #641
The type of muscle found only in the heart is:
A. Skeletal muscle
B. Cardiac muscle
C. Smooth muscle
D. Visceral muscle
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Correct Answer: Option B

Explanation:
Cardiac muscle is striated, branched, and involuntary, with intercalated discs containing gap junctions for synchronized contraction. It is unique to the heart wall. Smooth muscle is non-striated and involuntary in visceral organs, skeletal muscle is striated and voluntary. Cardiac muscle exhibits autorhythmicity.
This question belongs to: Science Biology
Question #642
The process of introducing DNA into bacterial cells by applying a brief electrical pulse is:
A. Microinjection
B. Biolistics
C. Heat shock
D. Electroporation
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Correct Answer: Option D

Explanation:
Electroporation uses an electric field to create temporary pores in the cell membrane, allowing DNA to enter. Heat shock is a chemical method using CaCl₂ and temperature shift, microinjection physically injects DNA into cells, biolistics is a gene gun for plant cells. Electroporation is efficient for many cell types.
This question belongs to: Science Biology
Question #643
The layer of the skin that contains blood vessels, nerves, and hair follicles is the:
A. Dermis
B. Epidermis
C. Stratum corneum
D. Hypodermis
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Correct Answer: Option A

Explanation:
The dermis, lying beneath the epidermis, is a connective tissue layer containing collagen and elastin fibers, blood vessels, nerve endings, sweat glands, hair follicles, and sebaceous glands. The epidermis is the outermost protective layer, the hypodermis is subcutaneous fat, and the stratum corneum is the outermost part of the epidermis.
This question belongs to: Science Biology
Question #644
The process by which plants convert glucose into starch is:
A. Polymerization
B. Photosynthesis
C. Translocation
D. Respiration
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Correct Answer: Option A

Explanation:
Glucose produced during photosynthesis is often polymerized into starch (a polysaccharide) for storage in chloroplasts or amyloplasts. This is an anabolic polymerization process. Photosynthesis produces glucose, respiration breaks it down, translocation is transport of solutes. Starch is a reserve carbohydrate.
This question belongs to: Science Biology
Question #645
The amount of air that remains in the lungs after a normal tidal expiration is the:
A. Functional residual capacity
B. Inspiratory capacity
C. Total lung capacity
D. Vital capacity
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Correct Answer: Option A

Explanation:
Functional residual capacity (FRC) is the volume of air in the lungs at the end of a normal expiration (ERV + RV). It prevents alveolar collapse and buffers gas concentrations. Vital capacity is max exhaled after max inhalation, total lung capacity is max air lungs can hold, inspiratory capacity is max inhaled after normal exhalation.
This question belongs to: Science Biology
Question #646
The symbiotic nitrogen-fixing cyanobacterium that lives in Azolla leaves is:
A. Anabaena azollae
B. Rhizobium
C. Azotobacter
D. Nostoc
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Correct Answer: Option A

Explanation:
Anabaena azollae is a heterocystous cyanobacterium that lives symbiotically in the dorsal leaf cavities of the water fern Azolla. It fixes atmospheric nitrogen, providing a natural nitrogen source for rice paddies when Azolla is used as green manure. Nostoc is free-living or lichen symbiont, Rhizobium and Azotobacter are bacteria.
This question belongs to: Science Biology
Question #647
The gland that secretes the hormone calcitonin is the:
A. Parathyroid
B. Adrenal
C. Pituitary
D. Thyroid
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Correct Answer: Option D

Explanation:
Calcitonin is produced by the parafollicular (C) cells of the thyroid gland. It lowers blood calcium levels by inhibiting osteoclast activity and promoting calcium deposition in bones. Parathyroid hormone (from parathyroid glands) raises calcium. Adrenal and pituitary glands have other functions.
This question belongs to: Science Biology
Question #648
The technique used to separate cellular organelles based on their density is:
A. Electrophoresis
B. Chromatography
C. Centrifugation
D. Spectrophotometry
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Correct Answer: Option C

Explanation:
Differential centrifugation separates organelles by size and density by spinning homogenized cells at progressively higher speeds. Each pellet is enriched in a particular organelle. Density gradient centrifugation further refines separation. Electrophoresis separates by charge/size, chromatography by differential partitioning, spectrophotometry measures absorbance.
This question belongs to: Science Biology
Question #649
The disease caused by the human immunodeficiency virus (HIV) is:
A. Tuberculosis
B. Leukemia
C. Hepatitis
D. Acquired immunodeficiency syndrome (AIDS)
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Correct Answer: Option D

Explanation:
HIV attacks CD4+ T helper cells, progressively weakening the immune system, leading to AIDS, characterized by opportunistic infections and cancers. Hepatitis is liver inflammation often viral, tuberculosis is bacterial, leukemia is cancer of white blood cells. Antiretroviral therapy (ART) controls HIV replication.
This question belongs to: Science Biology
Question #650
The process by which mRNA is synthesized from DNA is:
A. Transcription
B. Transformation
C. Replication
D. Translation
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Correct Answer: Option A

Explanation:
Transcription, catalyzed by RNA polymerase, copies the genetic information from a DNA template into a complementary mRNA molecule. Translation then uses this mRNA to synthesize proteins. Replication duplicates DNA, transformation is DNA uptake by bacteria.
This question belongs to: Science Biology
Question #651
The organelle that modifies, sorts, and packages proteins for secretion is the:
A. Lysosome
B. Golgi apparatus
C. Rough ER
D. Mitochondria
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Correct Answer: Option B

Explanation:
The Golgi apparatus receives proteins from the rough ER, modifies them (e.g., glycosylation), sorts them, and packages them into vesicles for transport to the plasma membrane, lysosomes, or secretion. Lysosomes digest, rough ER synthesizes proteins, mitochondria generate ATP.
This question belongs to: Science Biology
Question #652
The vitamin that is required for the synthesis of clotting factors is:
A. Vitamin A
B. Vitamin C
C. Vitamin K
D. Vitamin E
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Correct Answer: Option C

Explanation:
Vitamin K is a cofactor for the enzyme γ-glutamyl carboxylase, which adds carboxyl groups to glutamic acid residues in clotting factors II, VII, IX, and X, allowing them to bind calcium and participate in coagulation. Deficiency leads to bleeding tendency.
This question belongs to: Science Biology
Question #653
The structure that connects bone to bone in a joint is:
A. Tendon
B. Ligament
C. Muscle
D. Cartilage
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Correct Answer: Option B

Explanation:
Ligaments are tough, fibrous connective tissue bands that connect bones to other bones, stabilizing joints. Tendons connect muscle to bone. Cartilage cushions joints. Muscles generate movement. Ligaments can stretch to a limited extent; excessive force causes sprains.
This question belongs to: Science Biology
Question #654
The disease characterized by the inability to produce insulin is:
A. Type 1 diabetes mellitus
B. Cushing's syndrome
C. Diabetes insipidus
D. Type 2 diabetes mellitus
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Correct Answer: Option A

Explanation:
Type 1 diabetes mellitus is an autoimmune disease where beta cells of the pancreas are destroyed, leading to little or no insulin production. Patients require insulin injections. Type 2 involves insulin resistance. Diabetes insipidus involves ADH deficiency, Cushing's syndrome is cortisol excess.
This question belongs to: Science Biology
Question #655
The region of the root that provides protection to the growing tip is the:
A. Maturation zone
B. Root cap
C. Elongation zone
D. Meristematic zone
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Correct Answer: Option B

Explanation:
The root cap is a thimble-like mass of parenchyma cells covering the apical meristem, protecting it as the root pushes through the soil. It also secretes mucilage to ease passage. Cells are constantly sloughed off and replaced. The meristematic zone is where cells divide.
This question belongs to: Science Biology
Question #656
The cell division that reduces the chromosome number from diploid to haploid is:
A. Mitosis
B. Binary fission
C. Meiosis II
D. Meiosis I
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Correct Answer: Option D

Explanation:
Meiosis I is the reductional division where homologous chromosomes separate, resulting in two haploid cells with duplicated chromatids. Meiosis II is equational, separating sister chromatids. Mitosis maintains the diploid number. Meiosis ensures genetic variation and gamete formation.
This question belongs to: Science Biology
Question #657
The animal that has a notochord throughout its life is:
A. Frog
B. Amphioxus
C. Lizard
D. Human
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Correct Answer: Option B

Explanation:
Amphioxus (Branchiostoma) is a cephalochordate that retains the notochord, dorsal nerve cord, and pharyngeal slits throughout its life. In vertebrates, the notochord is largely replaced by the vertebral column during development. Amphioxus is a key model for studying vertebrate origins.
This question belongs to: Science Biology
Question #658
The enzyme that catalyzes the conversion of pyruvate to acetyl-CoA is:
A. Citrate synthase
B. Lactate dehydrogenase
C. Pyruvate dehydrogenase
D. Pyruvate kinase
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Correct Answer: Option C

Explanation:
Pyruvate dehydrogenase complex (PDC) oxidatively decarboxylates pyruvate, producing acetyl-CoA, NADH, and CO₂ in the mitochondrial matrix, linking glycolysis to the Krebs cycle. Pyruvate kinase is in glycolysis, lactate dehydrogenase converts pyruvate to lactate, citrate synthase starts the Krebs cycle.
This question belongs to: Science Biology
Question #659
The structure that regulates the passage of food from the stomach to the small intestine is the:
A. Anal sphincter
B. Pyloric sphincter
C. Cardiac sphincter
D. Ileocecal valve
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Correct Answer: Option B

Explanation:
The pyloric sphincter is a ring of smooth muscle at the junction of the stomach and duodenum. It controls the release of chyme from the stomach into the small intestine in small amounts. The cardiac sphincter is between the esophagus and stomach, ileocecal valve between small and large intestine.
This question belongs to: Science Biology
Question #660
The hormone that stimulates the production of red blood cells is:
A. Insulin
B. Erythropoietin
C. Thrombopoietin
D. Aldosterone
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Correct Answer: Option B

Explanation:
Erythropoietin (EPO), produced mainly by the kidneys in response to low oxygen levels, stimulates the bone marrow to produce red blood cells. Insulin regulates glucose, thrombopoietin stimulates platelet production, aldosterone regulates sodium and potassium balance.
This question belongs to: Science Biology

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