Biology MCQs

Question #1521

The 'Hormone Resistin' is secreted primarily by adipose tissue in humans (and by macrophages in rodents). Its primary function is to:

A. Inhibit appetite

B. Stimulate fat storage

C. Enhance insulin sensitivity

D. Antagonize insulin action, promoting insulin resistance and increasing hepatic glucose production

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Correct Answer: Option D

Explanation:
Resistin is a cysteine-rich peptide hormone secreted primarily by adipose tissue in humans (though in rodents, it is mainly secreted by macrophages). Its name is derived from its proposed role in 'resistance' to insulin. Its primary function is to antagonize the action of insulin, thereby promoting insulin resistance. It does this by increasing hepatic glucose production (gluconeogenesis) and impairing glucose uptake by muscle and adipose tissue. Elevated levels of resistin are associated with obesity and type 2 diabetes, linking adiposity to insulin resistance.

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Question #1522

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The 'Hormone Leptin' acts on the hypothalamus to regulate energy balance. It does this primarily by binding to receptors in the:

A. Arcuate nucleus

B. Ventromedial hypothalamus

C. Suprachiasmatic nucleus

D. Lateral hypothalamus

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Correct Answer: Option A

Explanation:
Leptin is a hormone secreted by adipose tissue that signals the status of body fat stores to the brain. It acts primarily on the arcuate nucleus (ARC) of the hypothalamus. The ARC contains two key populations of neurons: one that co-expresses Neuropeptide Y (NPY) and Agouti-related peptide (AgRP), which stimulate appetite, and another that expresses Pro-opiomelanocortin (POMC) and Cocaine- and amphetamine-regulated transcript (CART), which suppress appetite. Leptin binds to receptors on these neurons, inhibiting the NPY/AgRP neurons and stimulating the POMC/CART neurons, thereby reducing appetite and increasing energy expenditure.

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Question #1523

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Consider the following statements about cell theory:
1. All living organisms are composed of cells.
2. The cell is the basic structural and functional unit of life.
3. All cells arise from pre-existing cells.
Which of the statements above are correct?

A. 1 and 3 only

B. 1 and 2 only

C. 1, 2, and 3

D. 2 and 3 only

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Correct Answer: Option C

Explanation:
The modern cell theory includes all three statements: (1) all organisms are made of cells, (2) the cell is the basic unit of life, and (3) cells arise from pre-existing cells (Omnis cellula e cellula). Thus, all three are correct. This theory was formulated by Schleiden, Schwann, and Virchow.

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Question #1524

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Assertion (A): Red blood cells lack a nucleus in mammals.
Reason (R): The absence of a nucleus allows more space for hemoglobin, increasing oxygen-carrying capacity.

A. A is false, but R is true.

B. Both A and R are true, and R is the correct explanation of A.

C. Both A and R are true, but R is not the correct explanation.

D. A is true, but R is false.

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Correct Answer: Option B

Explanation:
Mature mammalian RBCs are anucleate, having lost their nucleus during maturation. This provides more space for hemoglobin, enhancing oxygen transport. The reason correctly explains the assertion. Nucleated RBCs are found in other vertebrates.

This question belongs to: Science Biology

Question #1525

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Which of the following statements about prokaryotic cells is INCORRECT?

A. They possess 70S ribosomes.

B. They contain membrane-bound organelles.

C. Their genetic material is circular DNA.

D. They lack a well-defined nucleus.

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Correct Answer: Option B

Explanation:
Prokaryotic cells lack membrane-bound organelles such as mitochondria, ER, Golgi, etc. They have a nucleoid region, 70S ribosomes, and typically a single circular chromosome. Thus, the statement that they contain membrane-bound organelles is incorrect.

This question belongs to: Science Biology

Question #1526

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Consider the following statements regarding mitochondria:
1. They are double-membrane organelles.
2. They have their own 80S ribosomes.
3. They are the site of aerobic respiration.
Which of the statements is/are correct?

A. 2 and 3 only

B. 1 only

C. 1 and 3 only

D. 1, 2, and 3

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Correct Answer: Option C

Explanation:
Mitochondria have two membranes (outer and inner) and are the site of Krebs cycle and oxidative phosphorylation. They possess 70S ribosomes, not 80S. Hence, statements 1 and 3 are correct.

This question belongs to: Science Biology

Question #1527

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Assertion (A): Lysosomes are known as the 'suicidal bags' of the cell.
Reason (R): They contain hydrolytic enzymes that can digest the cell’s own components.

A. A false, R true.

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 true, R false.

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Correct Answer: Option B

Explanation:
Lysosomes are membrane-bound vesicles containing powerful hydrolytic enzymes. When they burst, they can digest cellular components, leading to autolysis. Hence, they are called suicidal bags. The reason correctly explains the assertion.

This question belongs to: Science Biology

Question #1528

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Which of the following statements about meiosis is correct?

A. Crossing over occurs during prophase I.

B. It consists of a single division.

C. It produces genetically identical daughter cells.

D. It maintains the chromosome number of the parent cell.

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Correct Answer: Option A

Explanation:
Meiosis involves two divisions, producing four haploid, genetically diverse cells. Crossing over between homologous chromosomes occurs during prophase I, leading to recombination. Thus, C is correct.

This question belongs to: Science Biology

Question #1529

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Consider the following statements about blood:
1. Red blood cells transport oxygen.
2. White blood cells are involved in immunity.
3. Platelets help in blood clotting.
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

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Correct Answer: Option D

Explanation:
All three statements are correct: RBCs contain hemoglobin for oxygen transport, WBCs (leukocytes) defend against pathogens, and platelets (thrombocytes) initiate blood clotting.

This question belongs to: Science Biology

Question #1530

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Assertion (A): The human heart is myogenic.
Reason (R): It beats rhythmically due to signals from the brain.

A. Both A and R are true, but R is not the correct explanation.

B. A is true, but R is false.

C. Both A and R are true, and R is the correct explanation.

D. A is false, but R is true.

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Correct Answer: Option B

Explanation:
The heart is myogenic because the heartbeat originates in the SA node within the heart itself, not from brain signals. The brain can modulate the rate but not initiate. Thus, A is true, but R is false.

This question belongs to: Science Biology

Question #1531

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Which of the following statements about DNA is correct?

A. It is located in the nucleus in eukaryotes.

B. It contains the sugar ribose.

C. Adenine pairs with guanine.

D. It is usually single-stranded.

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Correct Answer: Option A

Explanation:
DNA is primarily located in the nucleus of eukaryotic cells. It contains deoxyribose (not ribose), is double-stranded, and adenine pairs with thymine. Thus, D is correct.

This question belongs to: Science Biology

Question #1532

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Consider the following statements regarding photosynthesis:
1. Light reactions occur in the thylakoid membranes.
2. Oxygen is released from carbon dioxide.
3. ATP and NADPH are produced in the light reactions.
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

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Correct Answer: Option C

Explanation:
Light reactions occur in thylakoid membranes, producing ATP, NADPH, and oxygen. Oxygen comes from water (photolysis), not CO₂. So statement 2 is incorrect. 1 and 3 are correct.

This question belongs to: Science Biology

Question #1533

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Assertion (A): The bacterial cell wall is composed of peptidoglycan.
Reason (R): Peptidoglycan provides structural strength and prevents osmotic lysis.

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.

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Correct Answer: Option B

Explanation:
Bacterial cell walls contain peptidoglycan (murein), a unique polymer that maintains cell shape and protects against osmotic pressure. The reason correctly explains why peptidoglycan is essential.

This question belongs to: Science Biology

Question #1534

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Which of the following statements about viruses is INCORRECT?

A. They reproduce by binary fission.

B. They can have either DNA or RNA as genetic material.

C. They are obligate intracellular parasites.

D. They lack metabolic machinery.

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Correct Answer: Option A

Explanation:
Viruses do not reproduce by binary fission; they replicate by hijacking host cell machinery. Binary fission is a method of asexual reproduction in bacteria. All other statements are correct.

This question belongs to: Science Biology

Question #1535

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Identify the correct statement regarding the human respiratory system:

A. The trachea is also called the voice box.

B. Alveoli are the main sites of gas exchange.

C. Pulmonary veins carry deoxygenated blood.

D. The diaphragm is made of smooth muscle.

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Correct Answer: Option B

Explanation:
Alveoli are thin-walled air sacs where O₂ and CO₂ exchange occurs. The voice box is the larynx; diaphragm is skeletal muscle; pulmonary veins carry oxygenated blood.

This question belongs to: Science Biology

Question #1536

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Consider the following statements about the endocrine system:
1. The pituitary gland is the master gland.
2. Thyroxine regulates basal metabolic rate.
3. Adrenaline decreases heart rate during stress.
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

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Correct Answer: Option C

Explanation:
The pituitary controls many glands (master gland). Thyroxine from the thyroid increases BMR. Adrenaline increases heart rate during stress, not decreases. So 1 and 2 are correct.

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Question #1537

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Assertion (A): Bile juice contains digestive enzymes.
Reason (R): Bile emulsifies fats to aid their digestion.

A. A is true, but R is false.

B. Both A and R are true, and R is the correct explanation.

C. A is false, but R is true.

D. Both A and R are true, but R is not the correct explanation.

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Correct Answer: Option C

Explanation:
Bile does not contain digestive enzymes; it contains bile salts that emulsify fats, increasing surface area for lipase action. Thus, A is false, R is true.

This question belongs to: Science Biology

Question #1538

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Which of the following statements about genetics is correct?

A. Homozygous individuals have two different alleles for a trait.

B. Mendel’s law of segregation states that allele pairs separate during gamete formation.

C. A monohybrid cross gives a phenotypic ratio of 9:3:3:1.

D. Phenotype refers to the genetic makeup of an organism.

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Correct Answer: Option B

Explanation:
Mendel’s first law (segregation) states that the two alleles for a trait separate during gamete formation. Homozygous individuals have identical alleles; phenotype is observable trait; a monohybrid ratio is 3:1.

This question belongs to: Science Biology

Question #1539

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Consider the following statements about enzymes:
1. They are biological catalysts.
2. They are consumed in the reaction.
3. They lower the activation energy of reactions.
Which of the above is/are correct?

A. 2 and 3 only

B. 1 and 3 only

C. 1, 2, and 3

D. 1 and 2 only

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Correct Answer: Option B

Explanation:
Enzymes speed up reactions by lowering activation energy and are not consumed; they remain unchanged after the reaction. Thus, statement 2 is false. 1 and 3 are correct.

This question belongs to: Science Biology

Question #1540

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Assertion (A): Xerophytes have a thick cuticle.
Reason (R): Thick cuticle reduces water loss in dry environments.

A. Both A and R are true, and R is the correct explanation.

B. A false, R true.

C. Both A and R are true, but R is not the correct explanation.

D. A true, R false.

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Correct Answer: Option A

Explanation:
Xerophytes (desert plants) have adaptations like thick cuticle, sunken stomata, and reduced leaves to minimize transpiration and conserve water. The reason correctly explains the adaptation.

This question belongs to: Science Biology

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