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 47 of 103
Question #921
Which enzyme present in the stomach digests proteins?
A. Pepsin
B. Trypsin
C. Lipase
D. Ptyalin
Discuss
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Correct Answer: Option A

Explanation:
Pepsin is a protease secreted by chief cells in the stomach as inactive pepsinogen, activated by HCl. It breaks proteins into peptides. Ptyalin is salivary amylase, trypsin is a pancreatic protease, lipase digests fats.
This question belongs to: Science Biology
Question #922
The valve between the right atrium and right ventricle is the:
A. Aortic semilunar valve
B. Pulmonary semilunar valve
C. Tricuspid valve
D. Mitral valve
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Correct Answer: Option C

Explanation:
The tricuspid valve has three cusps and prevents backflow of blood from the right ventricle to the right atrium during contraction. The mitral (bicuspid) valve is on the left side. Semilunar valves are at the ventricular outlets.
This question belongs to: Science Biology
Question #923
The functional unit of the human lung is the:
A. Villus
B. Neuron
C. Alveolus
D. Nephron
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Correct Answer: Option C

Explanation:
Alveoli are tiny air sacs surrounded by capillaries where gas exchange (O₂ and CO₂) occurs. Nephrons are kidney units, neurons nerve cells, villi intestinal projections. The lungs contain millions of alveoli to maximize surface area.
This question belongs to: Science Biology
Question #924
The hormone that lowers blood calcium by depositing it in bones is:
A. Insulin
B. Calcitonin
C. Thyroxine
D. Parathyroid hormone
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Correct Answer: Option B

Explanation:
Calcitonin, secreted by the thyroid gland, reduces blood calcium by inhibiting osteoclast activity and promoting calcium deposition in bones. Parathyroid hormone raises calcium. Thyroxine regulates metabolism, insulin lowers blood glucose.
This question belongs to: Science Biology
Question #925
Which of the following diseases is transmitted by the bite of an infected female Anopheles mosquito?
A. Filariasis
B. Chikungunya
C. Malaria
D. Dengue
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Correct Answer: Option C

Explanation:
Malaria, caused by Plasmodium parasites, is transmitted by the female Anopheles mosquito. Dengue and chikungunya are transmitted by Aedes mosquito, filariasis by Culex mosquito. Malaria remains a major global health concern.
This question belongs to: Science Biology
Question #926
The deficiency of vitamin B₁ causes:
A. Pellagra
B. Beriberi
C. Scurvy
D. Rickets
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Correct Answer: Option B

Explanation:
Beriberi results from thiamine (B₁) deficiency, characterized by neurological and cardiovascular symptoms. Scurvy is vitamin C deficiency, pellagra niacin (B₃), rickets vitamin D. Thiamine is a coenzyme in carbohydrate metabolism.
This question belongs to: Science Biology
Question #927
In DNA, the base complementary to guanine is:
A. Cytosine
B. Adenine
C. Uracil
D. Thymine
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Correct Answer: Option A

Explanation:
In DNA, guanine (G) pairs with cytosine (C) via three hydrogen bonds. Adenine pairs with thymine (two bonds). Uracil replaces thymine in RNA. Complementary base pairing is key to DNA structure and replication.
This question belongs to: Science Biology
Question #928
Mendel's experiments were performed on which plant?
A. Rice
B. Pea (Pisum sativum)
C. Maize
D. Wheat
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Correct Answer: Option B

Explanation:
Gregor Mendel conducted his classic hybridization experiments on garden pea (Pisum sativum) between 1856 and 1863, establishing the fundamental laws of inheritance. He selected seven contrasting characters.
This question belongs to: Science Biology
Question #929
The theory of 'use and disuse' was proposed by:
A. Alfred Wallace
B. Jean-Baptiste Lamarck
C. August Weismann
D. Charles Darwin
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Correct Answer: Option B

Explanation:
Lamarck proposed that organs used extensively develop and those not used degenerate, and these acquired traits are inherited (inheritance of acquired characters). Darwin's theory is natural selection, Wallace independently proposed natural selection, Weismann disproved Lamarckism.
This question belongs to: Science Biology
Question #930
The ultimate source of energy for all ecosystems is:
A. Water
B. Geothermal heat
C. Sun
D. Wind
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Correct Answer: Option C

Explanation:
Solar energy is captured by photosynthetic autotrophs and converted to chemical energy, which then flows through food chains. Except for deep-sea hydrothermal vents relying on chemosynthesis, the sun powers virtually all life on Earth.
This question belongs to: Science Biology
Question #931
Which of the following is a non-biodegradable pollutant?
A. Cotton cloth
B. Plastic
C. Paper
D. Vegetable waste
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Correct Answer: Option B

Explanation:
Plastics are synthetic polymers that resist microbial decomposition and persist in the environment for hundreds of years, causing pollution. Paper, cotton, and vegetable waste are biodegradable and broken down by decomposers.
This question belongs to: Science Biology
Question #932
The technique of polymerase chain reaction (PCR) is used to:
A. Separate DNA fragments by size
B. Amplify a specific DNA sequence
C. Sequence DNA
D. Cut DNA at specific sites
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Correct Answer: Option B

Explanation:
PCR is an in vitro technique to exponentially amplify a specific DNA segment using primers, Taq polymerase, and thermal cycles. Electrophoresis separates DNA, sequencing determines base order, restriction enzymes cut DNA.
This question belongs to: Science Biology
Question #933
The scientist who discovered the bacterium that causes anthrax was:
A. Joseph Lister
B. Louis Pasteur
C. Robert Koch
D. Edward Jenner
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Correct Answer: Option C

Explanation:
Robert Koch identified Bacillus anthracis as the causative agent of anthrax in 1876, establishing Koch's postulates for proving microbial disease causation. Pasteur developed vaccines, Jenner smallpox vaccine, Lister antiseptic surgery.
This question belongs to: Science Biology
Question #934
Assertion (A): Viruses are considered obligate intracellular parasites. Reason (R): They lack their own metabolic machinery and require a host cell to multiply.
A. A is false, but R is true.
B. A is true, but R is false.
C. Both A and R are true, but R is not the correct explanation.
D. Both A and R are true, and R is the correct explanation of A.
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Correct Answer: Option D

Explanation:
Viruses are non-living outside a host; they cannot carry out metabolic processes or reproduce independently. They hijack the host cell's machinery to replicate. Thus, they are obligate intracellular parasites. The reason correctly explains the assertion.
This question belongs to: Science Biology
Question #935
The plant hormone that promotes seed germination by breaking dormancy is:
A. Gibberellin
B. Ethylene
C. Abscisic acid
D. Auxin
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Correct Answer: Option A

Explanation:
Gibberellins stimulate the synthesis of hydrolytic enzymes (e.g., amylase) that mobilize stored food reserves, promoting germination. Abscisic acid induces and maintains dormancy. Ethylene promotes ripening, auxin cell elongation.
This question belongs to: Science Biology
Question #936
The organ of the human body that filters blood and forms urine is the:
A. Kidney
B. Lung
C. Liver
D. Heart
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Correct Answer: Option A

Explanation:
Kidneys are bean-shaped organs that filter waste products, excess water, and electrolytes from the blood to form urine. The liver processes nutrients and toxins, the heart pumps blood, the lungs exchange gases.
This question belongs to: Science Biology
Question #937
Which of the following blood cells is responsible for humoral immunity?
A. Neutrophils
B. B lymphocytes
C. Macrophages
D. T lymphocytes
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Correct Answer: Option B

Explanation:
B lymphocytes differentiate into plasma cells that produce antibodies (immunoglobulins) against specific antigens, providing humoral immunity. T cells mediate cellular immunity, macrophages and neutrophils are phagocytes.
This question belongs to: Science Biology
Question #938
The condition caused by excessive secretion of thyroxine is:
A. Myxedema
B. Cretinism
C. Simple goiter
D. Exophthalmic goiter (Graves' disease)
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Correct Answer: Option D

Explanation:
Graves' disease is an autoimmune hyperthyroidism characterized by exophthalmos (bulging eyes), weight loss, and tachycardia. Myxedema is adult hypothyroidism, cretinism congenital hypothyroidism, simple goiter iodine deficiency.
This question belongs to: Science Biology
Question #939
The process by which pollen grains are transferred to the stigma is called:
A. Pollination
B. Fertilization
C. Germination
D. Dispersal
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Correct Answer: Option A

Explanation:
Pollination is the transfer of pollen from the anther to the stigma of a flower, a prerequisite for fertilization. Fertilization is the fusion of male and female gametes. Germination is seed growth, dispersal is seed spreading.
This question belongs to: Science Biology
Question #940
The enzyme that catalyzes the synthesis of RNA from a DNA template is:
A. Ligase
B. Helicase
C. DNA polymerase
D. RNA polymerase
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Correct Answer: Option D

Explanation:
RNA polymerase binds to the promoter region of DNA and synthesizes a complementary RNA strand during transcription. DNA polymerase synthesizes DNA, ligase joins DNA fragments, helicase unwinds DNA.
This question belongs to: Science Biology

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