The functional unit of striated muscle contraction from one Z-line to the next is the: MCQ with Answer and Explanation

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The functional unit of striated muscle contraction from one Z-line to the next is the:

A. Sarcomere

B. Sarcolemma

C. Myofibril

D. Sarcoplasm

Answer: Option A

Solution (By JKSSB Mock Tests)

A sarcomere is the segment between two Z-lines (Z-discs) and is the basic contractile unit of skeletal and cardiac muscle. It contains actin (thin) and myosin (thick) filaments. Sarcolemma is the plasma membrane, sarcoplasm is cytoplasm, myofibril is a bundle of contractile filaments. Shortening of sarcomeres leads to muscle contraction per sliding filament theory.

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Question #1

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Consider statements about scientists: 1. Robert Hooke coined the term 'cell'. 2. Antonie van Leeuwenhoek discovered the cell nucleus. 3. Matthias Schleiden proposed that all plants are made of cells. Which are correct?

A. 1 and 2 only

B. 1, 2 and 3

C. 1 and 3 only

D. 2 and 3 only

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Correct Answer: Option C

Explanation:
Robert Hooke observed cork tissue in 1665 and coined the term 'cell' to describe the box-like structures. Matthias Schleiden, a botanist, concluded in 1838 that all plants are composed of cells, forming a core tenet of the cell theory. The cell nucleus was discovered by Robert Brown in 1831, not Antonie van Leeuwenhoek, who is famous for discovering living microorganisms. Thus, statements 1 and 3 are correct.

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Question #2

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Identify the INCORRECT statement about the human ear:

A. The eardrum vibrates in response to sound waves.

B. The auditory nerve carries impulses to the brain.

C. The cochlea is responsible for balance.

D. The ossicles amplify sound vibrations.

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Correct Answer: Option C

Explanation:
The cochlea is for hearing; the vestibular apparatus (semicircular canals, utricle, saccule) is for balance. So C is incorrect.

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Question #3

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The 'Hormone Gastrin' is secreted by the 'G cells' of the stomach and primarily stimulates:

A. The gastric glands to secrete hydrochloric acid (HCl) and pepsinogen

B. The gall bladder to contract

C. The pancreas to secrete bicarbonate

D. The liver to produce bile

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Correct Answer: Option A

Explanation:
Gastrin is a peptide hormone produced by the G cells (gastrin cells) located in the pyloric antrum of the stomach. Its primary function is to stimulate the parietal cells of the gastric glands to secrete hydrochloric acid (HCl) and the chief cells to secrete pepsinogen. This prepares the stomach for the digestion of food. Gastrin also stimulates gastric motility and growth of the gastric mucosa. Secretin and CCK stimulate the pancreas and gall bladder.

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