Which of the following is a characteristic feature of cardiac muscle?
A. Multinucleated syncytium
B. Voluntary control
C. Branched fibres with intercalated discs
D. Spindle-shaped cells
Answer: Option C
Solution (By JKExamLibrary)
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.
Explanation:
Active vitamin D (calcitriol) induces synthesis of calcium-binding proteins in the intestinal mucosa, enhancing calcium absorption. Calcium is vital for bones, teeth, blood clotting, and nerve-muscle function.
Explanation:
Cataract is clouding of the crystalline lens leading to decreased vision, commonly age-related. Glaucoma is optic nerve damage often due to increased intraocular pressure. Myopia is nearsightedness, hypermetropia is farsightedness. Cataract surgery replaces the lens with an artificial one.
Explanation:
Robert Hooke observed thin slices of cork under a microscope he designed and saw honeycomb-like compartments which he termed 'cells' in his 1665 book 'Micrographia'. Leeuwenhoek discovered living cells (bacteria, protozoa). Brown discovered the nucleus (1831), and Virchow proposed that all cells arise from pre-existing cells (1855). Hooke's cells were dead, empty cell walls of cork.
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