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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Question #1601
Assertion (A): The blood-brain barrier protects the brain.
Reason (R): It is formed by tight junctions between endothelial cells of brain capillaries.
A. Both A and R are true, but R is not the correct explanation.
B. Both A and R are true, and R is the correct explanation.
C. A false, R true.
D. A true, R false.
Discuss
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Correct Answer: Option B

Explanation:
The BBB restricts entry of pathogens and large molecules, maintaining brain homeostasis. Tight junctions between capillary endothelial cells are the structural basis. R explains A.
This question belongs to: Science Biology
Question #1602
Which of the following statements about genes and alleles is correct?
A. A gene is a variant form of an allele.
B. Recessive alleles are always expressed in the phenotype.
C. Dominant alleles mask the effect of recessive alleles.
D. An individual with two identical alleles is heterozygous.
Discuss
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Correct Answer: Option C

Explanation:
Dominant alleles express their trait when present, masking recessive alleles. A gene is a DNA segment; alleles are its variants. Homozygous means identical alleles, recessive expressed only in homozygous state.
This question belongs to: Science Biology
Question #1603
Identify the correct statement about the circulatory system:
A. The pulmonary artery carries oxygenated blood.
B. Veins have thin, elastic walls compared to arteries.
C. Capillaries have valves to prevent backflow.
D. Arteries always carry oxygenated blood.
Discuss
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Correct Answer: Option B

Explanation:
Veins have thinner walls than arteries and contain valves. The pulmonary artery carries deoxygenated blood, and arteries normally (except pulmonary) carry oxygenated blood.
This question belongs to: Science Biology
Question #1604
Consider the following statements about the human kidney:
1. It filters blood and forms urine.
2. It reabsorbs glucose in the collecting duct.
3. It secretes erythropoietin.
Which of the above is/are correct?
A. 2 and 3 only
B. 1 and 2 only
C. 1 and 3 only
D. 1, 2, and 3
Discuss
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Correct Answer: Option C

Explanation:
Kidneys filter blood (1) and produce erythropoietin (3). Glucose reabsorption occurs in the proximal tubule, not collecting duct. So 2 is incorrect.
This question belongs to: Science Biology
Question #1605
Assertion (A): The color of urine is due to urobilin.
Reason (R): Urobilin is a breakdown product of hemoglobin.
A. Both A and R are true, and R is the correct explanation.
B. Both A and R are true, but R is not the correct explanation.
C. A false, R true.
D. A true, R false.
Discuss
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Correct Answer: Option A

Explanation:
Urobilin is derived from bilirubin, a heme breakdown product, and gives urine its yellow color. R is true and explains A.
This question belongs to: Science Biology
Question #1606
Which of the following statements about enzymes is correct?
A. Enzymes are non-specific in their action.
B. Cofactors are always organic molecules.
C. Enzymes increase the activation energy of reactions.
D. All enzymes are proteins.
Discuss
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Correct Answer: Option D

Explanation:
Almost all enzymes are proteins (except ribozymes). They lower activation energy, are highly specific, and cofactors can be inorganic (metal ions) or organic (coenzymes).
This question belongs to: Science Biology
Question #1607
Identify the INCORRECT statement about the human digestive system:
A. The stomach secretes hydrochloric acid.
B. The large intestine produces digestive enzymes.
C. The pancreas secretes amylase.
D. The small intestine is the main site of nutrient absorption.
Discuss
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Correct Answer: Option B

Explanation:
The large intestine does not produce digestive enzymes; it absorbs water and electrolytes. The small intestine and pancreas produce enzymes.
This question belongs to: Science Biology
Question #1608
Consider the following statements about the greenhouse effect:
1. Greenhouse gases trap heat in the atmosphere.
2. CO₂, methane, and water vapor are greenhouse gases.
3. The greenhouse effect is solely harmful.
Which of the above is/are correct?
A. 1, 2, and 3
B. 1 and 2 only
C. 2 and 3 only
D. 1 and 3 only
Discuss
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Correct Answer: Option B

Explanation:
The natural greenhouse effect keeps Earth warm enough for life; its enhancement causes global warming. Statement 3 is incorrect. 1 and 2 are correct.
This question belongs to: Science Biology
Question #1609
Assertion (A): The SA node is called the pacemaker of the heart.
Reason (R): It generates electrical impulses that initiate the heartbeat.
A. Both A and R are true, but R is not the correct explanation.
B. A true, R false.
C. Both A and R are true, and R is the correct explanation.
D. A false, R true.
Discuss
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Correct Answer: Option C

Explanation:
The sinoatrial node spontaneously depolarizes, setting the rhythm of the heart. The reason correctly explains its role as pacemaker.
This question belongs to: Science Biology
Question #1610
Which of the following statements about protein synthesis is correct?
A. tRNA contains the genetic code for the protein.
B. Transcription occurs in the cytoplasm.
C. Ribosomes are the sites of translation.
D. Translation converts DNA to mRNA.
Discuss
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Correct Answer: Option C

Explanation:
Ribosomes translate mRNA into protein. Transcription (DNA→mRNA) occurs in the nucleus (eukaryotes). mRNA carries the code, tRNA brings amino acids.
This question belongs to: Science Biology
Question #1611
Consider the following statements about the skeletal system:
1. Bones store calcium and phosphorus.
2. Red bone marrow produces blood cells.
3. Ligaments connect muscle to bone.
Which of the above is/are correct?
A. 2 and 3 only
B. 1, 2, and 3
C. 1 and 2 only
D. 1 and 3 only
Discuss
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Correct Answer: Option C

Explanation:
Bones store minerals (1) and contain marrow for hematopoiesis (2). Ligaments connect bone to bone; tendons connect muscle to bone. So 3 is incorrect.
This question belongs to: Science Biology
Question #1612
Assertion (A): The large central vacuole in plant cells helps maintain turgor pressure.
Reason (R): It stores water and solutes, creating osmotic pressure that pushes the cytoplasm against the cell wall.
A. A false, R true.
B. A true, R 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.
Discuss
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Correct Answer: Option D

Explanation:
The vacuole’s solute concentration draws water, generating turgor pressure that maintains cell rigidity. This is essential for support in plants. R explains A.
This question belongs to: Science Biology
Question #1613
Which of the following statements about pollination is INCORRECT?
A. Anemophily is pollination by wind.
B. Entomophily is pollination by insects.
C. Zoophily involves animals.
D. Hydrophily occurs in terrestrial plants.
Discuss
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Correct Answer: Option D

Explanation:
Hydrophily is pollination by water and occurs in aquatic plants like Vallisneria and Zostera. Terrestrial plants do not use water for pollination. All other statements are correct.
This question belongs to: Science Biology
Question #1614
Identify the correct statement about the respiratory pigment:
A. Hemoglobin contains copper and is red.
B. Myoglobin stores oxygen in muscles.
C. Hemoglobin is found in white blood cells.
D. Hemocyanin contains iron and is blue.
Discuss
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Correct Answer: Option B

Explanation:
Myoglobin is an oxygen-binding protein in muscle. Hemoglobin contains iron and is red; hemocyanin contains copper and is blue. Hemoglobin is in RBCs.
This question belongs to: Science Biology
Question #1615
Consider the following statements about immunity:
1. Innate immunity is non-specific.
2. Antibodies are produced by T-cells.
3. Vaccination provides active immunity.
Which of the above is/are correct?
A. 1 and 2 only
B. 2 and 3 only
C. 1, 2, and 3
D. 1 and 3 only
Discuss
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Correct Answer: Option D

Explanation:
Innate immunity is non-specific; vaccination induces active immunity. Antibodies are made by B-cells, not T-cells. So 2 is incorrect.
This question belongs to: Science Biology
Question #1616
Assertion (A): Oxygen is required for aerobic respiration.
Reason (R): Oxygen acts as the final electron acceptor in the electron transport chain.
A. Both A and R are true, and R is the correct explanation.
B. A true, R false.
C. A false, R true.
D. Both A and R are true, but R is not the correct explanation.
Discuss
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Correct Answer: Option A

Explanation:
In aerobic respiration, oxygen accepts electrons at the end of the ETC, forming water. Without it, the chain would halt. This directly explains why oxygen is required.
This question belongs to: Science Biology
Question #1617
Which of the following statements about biotechnology is correct?
A. Restriction enzymes join DNA fragments.
B. Plasmids are used as vectors because they can replicate independently.
C. Tissue culture produces genetically diverse plants.
D. Bt cotton is resistant to all pesticides.
Discuss
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Correct Answer: Option B

Explanation:
Plasmids have an origin of replication, making them effective cloning vectors. Restriction enzymes cut DNA, tissue culture produces clones, Bt cotton targets specific insects.
This question belongs to: Science Biology
Question #1618
Identify the INCORRECT statement about the human skeleton:
A. The rib cage protects the heart and lungs.
B. The vertebral column protects the spinal cord.
C. The skull protects the brain.
D. The humerus is a bone of the leg.
Discuss
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Correct Answer: Option D

Explanation:
The humerus is the upper arm bone. The femur is the thigh bone. So C is incorrect.
This question belongs to: Science Biology
Question #1619
Consider the following statements about the pancreas:
1. It has both endocrine and exocrine functions.
2. Alpha cells secrete insulin.
3. Beta cells secrete glucagon.
Which of the above is/are correct?
A. 2 and 3
B. 1 only
C. 3 only
D. 2 only
Discuss
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Correct Answer: Option B

Explanation:
The pancreas is a mixed gland (1). Alpha cells secrete glucagon, beta cells insulin. Thus, 2 and 3 are swapped and incorrect.
This question belongs to: Science Biology
Question #1620
Assertion (A): Double circulation is seen in birds and mammals.
Reason (R): It ensures complete separation of oxygenated and deoxygenated blood.
A. Both A and R are true, and R is the correct explanation.
B. A false, R true.
C. A true, R false.
D. Both A and R are true, but R is not the correct explanation.
Discuss
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Correct Answer: Option A

Explanation:
Double circulation (pulmonary and systemic) with a four-chambered heart keeps oxygenated and deoxygenated blood separate, increasing efficiency. R correctly explains A.
This question belongs to: Science Biology

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