The scientist who discovered the cell nucleus was:
A. Robert Hooke
B. Robert Brown
C. Theodor Schwann
D. Matthias Schleiden
Answer: Option B
Solution (By JKSSB Mock Tests)
Robert Brown, a Scottish botanist, discovered and named the nucleus in 1831 while studying orchid epidermal cells. Hooke coined 'cell', Schleiden and Schwann formulated cell theory. Brown's observation was pivotal.
Explanation:
Natural killer (NK) cells were discovered in the 1970s by Rolf Kiessling and others. They are part of innate immunity, killing virus-infected and tumor cells.
Explanation:
A human zygote is diploid (2n = 46), formed by the fusion of a haploid sperm (23) and a haploid ovum (23). It contains 22 pairs of autosomes and one pair of sex chromosomes (XX or XY). Mitotic division then produces all somatic cells. Gametes are haploid (23).
Explanation:
Calcitonin, secreted by parafollicular (C) cells of the thyroid, decreases blood calcium by inhibiting osteoclasts and promoting calcium deposition in bones. Parathyroid hormone (PTH) raises calcium.
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