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 #1681
Assertion (A): The plasma membrane is selectively permeable.
Reason (R): It allows some substances to pass through while blocking others.
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 true, R false.
D. A false, R true.
Discuss
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Correct Answer: Option A

Explanation:
Selective permeability means the membrane controls entry and exit of substances based on size, charge, and solubility. R defines this property and explains A.
This question belongs to: Science Biology
Question #1682
Which of the following statements about the food web is correct?
A. It represents interconnected food chains.
B. Decomposers are not part of food webs.
C. Energy flow in a food web is cyclic.
D. A food web consists of a single linear chain.
Discuss
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Correct Answer: Option A

Explanation:
A food web is a network of food chains, showing multiple feeding relationships. Energy flow is unidirectional, and decomposers are integral.
This question belongs to: Science Biology
Question #1683
Consider the following statements about the human heart:
1. The pericardium is a protective sac around the heart.
2. The endocardium lines the heart chambers.
3. The myocardium is the outermost layer.
Which of the above is/are correct?
A. 1 and 2 only
B. 2 and 3 only
C. 1 and 3 only
D. 1, 2, and 3
Discuss
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Correct Answer: Option A

Explanation:
Pericardium is outer sac, endocardium inner lining. Myocardium is the middle muscular layer; the outermost is epicardium (visceral pericardium). So 3 is incorrect.
This question belongs to: Science Biology
Question #1684
Assertion (A): Saliva contains the enzyme amylase.
Reason (R): Amylase begins the digestion of starch in the mouth.
A. A true, R false.
B. Both A and R are true, and R is the correct explanation.
C. Both A and R are true, but R is not the correct explanation.
D. A false, R true.
Discuss
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Correct Answer: Option B

Explanation:
Salivary amylase (ptyalin) hydrolyzes starch into maltose and dextrins, initiating carbohydrate digestion. The reason explains the presence of amylase in saliva.
This question belongs to: Science Biology
Question #1685
Identify the correct statement about the cell nucleus:
A. It contains the nucleolus, which synthesizes ribosomal RNA.
B. It is absent in all eukaryotic cells.
C. DNA replication occurs in the cytoplasm.
D. It is surrounded by a single membrane.
Discuss
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Correct Answer: Option A

Explanation:
The nucleolus makes rRNA and assembles ribosomal subunits. Nucleus has a double membrane, is present in eukaryotes, and is the site of DNA replication.
This question belongs to: Science Biology
Question #1686
Consider the following statements about enzymes:
1. Enzyme activity is affected by pH.
2. All enzymes have an optimum temperature around 37°C.
3. Enzymes are reusable.
Which of the above is/are correct?
A. 1 and 3 only
B. 1 and 2 only
C. 2 and 3 only
D. 1, 2, and 3
Discuss
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Correct Answer: Option A

Explanation:
Enzyme activity depends on pH and temperature; they are not consumed (reusable). Optimum temperature varies; human enzymes around 37°C, but bacterial enzymes can be higher. So 2 is not universally true.
This question belongs to: Science Biology
Question #1687
Assertion (A): Gymnosperms do not produce fruits.
Reason (R): Their seeds are not enclosed within an ovary.
A. A false, R true.
B. Both A and R are true, but R is not the correct explanation.
C. Both A and R are true, and R is the correct explanation.
D. A true, R false.
Discuss
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Correct Answer: Option C

Explanation:
Gymnosperms have naked seeds on cones, not in an ovary; hence no fruit. Angiosperms have enclosed seeds. R correctly explains A.
This question belongs to: Science Biology
Question #1688
Which of the following statements about the human blood is correct?
A. A person with blood group AB can donate blood to all other groups.
B. Plasma does not contain water.
C. O-negative blood is the universal donor for red cells.
D. Rh-negative individuals have the Rh antigen.
Discuss
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Correct Answer: Option C

Explanation:
O negative lacks A, B, and Rh antigens, so it can be given to anyone (RBCs). AB is universal recipient. Rh-negative lacks Rh antigen. Plasma is 90% water.
This question belongs to: Science Biology
Question #1689
Consider the following statements about AIDS:
1. It is caused by a bacterium.
2. It weakens the immune system.
3. It can be transmitted by sharing needles.
Which of the above is/are correct?
A. 2 and 3 only
B. 1, 2, and 3
C. 1 and 3 only
D. 1 and 2 only
Discuss
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Correct Answer: Option A

Explanation:
AIDS is caused by HIV, a virus, not bacterium. It destroys CD4+ T-cells, weakening immunity, and spreads via blood/needles, sexual contact, etc. So 2 and 3 are correct.
This question belongs to: Science Biology
Question #1690
Assertion (A): The pancreas is a mixed gland.
Reason (R): It has exocrine acini secreting enzymes and endocrine islets secreting hormones.
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:
The pancreas secretes digestive enzymes (exocrine) and insulin/glucagon (endocrine). The reason correctly defines why it is mixed.
This question belongs to: Science Biology
Question #1691
Which of the following statements about the chloroplast is correct?
A. It is found in all eukaryotic cells.
B. It has 70S ribosomes in its outer membrane.
C. The stroma is the site of the Calvin cycle.
D. Thylakoids are stacked to form cristae.
Discuss
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Correct Answer: Option C

Explanation:
Calvin cycle occurs in the stroma. Chloroplasts are only in plants/algae; thylakoids stack into grana; cristae are in mitochondria; 70S ribosomes are in stroma, not membrane.
This question belongs to: Science Biology
Question #1692
Identify the correct statement about photosynthesis:
A. The light reactions occur in the stroma.
B. ATP and NADPH are produced during the Calvin cycle.
C. Photorespiration increases the efficiency of photosynthesis.
D. Rubisco is the enzyme that fixes CO₂ in the Calvin cycle.
Discuss
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Correct Answer: Option D

Explanation:
Rubisco catalyzes CO₂ fixation. Light reactions occur in thylakoids, ATP/NADPH are produced there, Calvin cycle uses them. Photorespiration reduces efficiency.
This question belongs to: Science Biology
Question #1693
Consider the following statements about the human excretory system:
1. ADH increases water reabsorption.
2. Aldosterone increases sodium reabsorption.
3. Renin converts angiotensinogen to angiotensin I.
Which of the above is/are correct?
A. 2 and 3 only
B. 1 and 3 only
C. 1 and 2 only
D. 1, 2, and 3
Discuss
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Correct Answer: Option D

Explanation:
All are correct: ADH (water), aldosterone (Na⁺), renin (angiotensinogen cleavage).
This question belongs to: Science Biology
Question #1694
Assertion (A): The cell wall of plants is freely permeable.
Reason (R): It allows water and dissolved substances to pass through.
A. A false, R true.
B. Both A and R are true, but R is not the correct explanation.
C. A true, R false.
D. Both A and R are true, and R is the correct explanation.
Discuss
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Correct Answer: Option D

Explanation:
The cell wall is porous and does not regulate entry; the plasma membrane is selectively permeable. Thus, the wall is freely permeable, and the reason explains it.
This question belongs to: Science Biology
Question #1695
Which of the following statements about the human immune system is correct?
A. Vaccines stimulate the production of antibodies and memory cells.
B. Active immunity is immediate and temporary.
C. Innate immunity is specific to particular pathogens.
D. Passive immunity involves the production of memory cells.
Discuss
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Correct Answer: Option A

Explanation:
Vaccines induce active immunity (antibodies + memory). Active takes time, passive is immediate but no memory. Innate is nonspecific.
This question belongs to: Science Biology
Question #1696
Identify the INCORRECT statement about carbohydrates:
A. Glycogen is the storage form in animals.
B. Cellulose is a storage carbohydrate in plants.
C. Starch is a polysaccharide.
D. They are composed of carbon, hydrogen, and oxygen.
Discuss
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Correct Answer: Option B

Explanation:
Cellulose is a structural polysaccharide, not storage. Starch is storage in plants. Glycogen is animal storage. So C is incorrect.
This question belongs to: Science Biology
Question #1697
Consider the following statements about the human heart:
1. The bicuspid valve is on the left side.
2. The tricuspid valve is on the right side.
3. The pulmonary valve prevents backflow into the right ventricle.
Which of the above is/are correct?
A. 1, 2, and 3
B. 1 and 2 only
C. 1 and 3 only
D. 2 and 3 only
Discuss
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Correct Answer: Option A

Explanation:
All three are correct: bicuspid (left AV), tricuspid (right AV), pulmonary valve at right ventricle exit.
This question belongs to: Science Biology
Question #1698
Assertion (A): Cilia and flagella are involved in cell movement.
Reason (R): They contain microtubules arranged in a 9+2 pattern.
A. Both A and R are true, and R is the correct explanation.
B. A true, R false.
C. Both A and R are true, but R is not the correct explanation.
D. A false, R true.
Discuss
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Correct Answer: Option A

Explanation:
Cilia and flagella are motile structures with a 9+2 axoneme of microtubules. Their movement propels the cell or moves fluids. R explains the structural basis.
This question belongs to: Science Biology
Question #1699
Consider statements about lysosomes: 1. They are formed by Golgi apparatus. 2. They contain hydrolytic enzymes. 3. They are involved in autophagy. Which are correct?
A. 2 and 3 only
B. 1 and 3 only
C. 1 and 2 only
D. 1, 2 and 3
Discuss
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Correct Answer: Option D

Explanation:
Lysosomes are membrane-bound vesicles budded off from the Golgi apparatus. They contain powerful hydrolytic enzymes capable of breaking down proteins, lipids, and nucleic acids. They play a crucial role in autophagy, digesting worn-out cellular organelles. Thus, all three statements are biologically accurate and correct.
This question belongs to: Science Biology
Question #1700
Consider statements about mitochondria: 1. They have a single membrane. 2. They contain their own circular DNA. 3. They are the site of aerobic respiration. Which are correct?
A. 1, 2 and 3
B. 1 and 2 only
C. 1 and 3 only
D. 2 and 3 only
Discuss
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Correct Answer: Option D

Explanation:
Mitochondria are double-membrane-bound organelles, possessing an outer smooth membrane and a highly folded inner membrane forming cristae. They contain their own circular DNA and 70S ribosomes, making them semi-autonomous. They are the primary site of aerobic respiration and ATP production. Statement 1 is incorrect as they have two membranes.
This question belongs to: Science Biology

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