Which of the following is a characteristic feature of cardiac muscle? MCQ with Answer and Explanation

Which of the following is a characteristic feature of cardiac muscle?
A. Multinucleated syncytium
B. Branched fibres with intercalated discs
C. Spindle-shaped cells
D. Voluntary control
Answer: Option B
Solution (By JKSSB Mock Tests)
Cardiac muscle cells are striated, branched, and connected by intercalated discs containing gap junctions for synchronized contraction. They are involuntary. Multinucleated syncytium is typical of skeletal muscle. Spindle-shaped non-striated cells characterize smooth muscle. Voluntary control is for skeletal muscle. Intercalated discs allow rapid ion passage, enabling the heart to function as a syncytium.

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Question #1
Consider statements about ribosomes: 1. They are non-membranous organelles. 2. Prokaryotic ribosomes are 80S. 3. They are the site of protein synthesis. Which are correct?
A. 1, 2 and 3
B. 1 and 3 only
C. 1 and 2 only
D. 2 and 3 only

Correct Answer: Option B


Explanation:
Ribosomes are dense, spherical, non-membranous structures composed of RNA and proteins. They are the cellular factories for protein synthesis. Prokaryotic ribosomes are 70S (50S + 30S subunits), while eukaryotic cytoplasmic ribosomes are 80S (60S + 40S subunits). Therefore, statements 1 and 3 are correct, but statement 2 is false.

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Question #2
The phenomenon of a plant flowering in response to the length of day is called:
A. Phototropism
B. Geotropism
C. Chemotropism
D. Photoperiodism

Correct Answer: Option D


Explanation:
Photoperiodism is the response of plants to the relative lengths of day and night, influencing flowering. Short-day plants (e.g., poinsettia) flower when day length is less than a critical period; long-day plants (e.g., spinach) flower when days are longer. Phototropism is growth towards light, geotropism to gravity, chemotropism to chemicals.

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Question #3
Which of the following is NOT a characteristic of prokaryotic cells?
A. Circular DNA
B. Presence of 70S ribosomes
C. Presence of membrane-bound organelles
D. Cell wall generally present

Correct Answer: Option C


Explanation:
Prokaryotes lack membrane-bound organelles like mitochondria, Golgi apparatus, and endoplasmic reticulum. They have 70S ribosomes, a single circular chromosome in a nucleoid, and typically a cell wall (except Mycoplasma). Eukaryotes possess membrane-bound organelles. This fundamental difference defines the two major cell types in the living world.

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