The 'Haversian system' or 'osteon' is the fundamental functional unit of compact bone in: MCQ with Answer and Explanation

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The 'Haversian system' or 'osteon' is the fundamental functional unit of compact bone in:

A. Cartilage

B. Mammalian bone

C. Bird bone

D. Fish bone

Answer: Option B

Solution (By JKExamLibrary)

The Haversian system (osteon) is the characteristic structural unit of compact (cortical) bone in mammals. It consists of a central Haversian canal (containing blood vessels and nerves) surrounded by concentric layers of calcified matrix called lamellae. Between the lamellae are small spaces called lacunae, which house osteocytes (bone cells). Canaliculi connect the lacunae. Bird bones are pneumatic (hollow), and cartilage lacks Haversian systems.

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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 true, R false.

B. A false, R true.

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.

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Correct Answer: Option D

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.

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Question #2

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Which class of antibody is the most abundant in human blood plasma?

A. IgE

B. IgM

C. IgG

D. IgA

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Correct Answer: Option C

Explanation:
Immunoglobulin G (IgG) is the most abundant antibody in human blood plasma, constituting about 75-80% of all antibodies. It is the only antibody that can cross the placenta, providing passive immunity to the fetus. IgG is crucial for long-term immunity, neutralizing toxins, viruses, and bacteria, and activating the complement system.

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Question #3

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Which of the following diseases is caused by the bacterium Clostridium tetani?

A. Pertussis (whooping cough)

B. Diphtheria

C. Botulism

D. Tetanus

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Correct Answer: Option D

Explanation:
Tetanus (lockjaw) is caused by the neurotoxin of Clostridium tetani, a soil bacterium that enters through wounds. The toxin causes muscle spasms and rigidity. Diphtheria is by Corynebacterium diphtheriae, pertussis by Bordetella pertussis, botulism by Clostridium botulinum (also a neurotoxin, but from food poisoning). Vaccination with DPT/tetanus toxoid prevents tetanus.

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