During which phase of the cell cycle does the centrosome duplicate?
A. S phase
B. G1 phase
C. G2 phase
D. M phase
Answer: Option A
Solution (By JKExamLibrary)
The centrosome, which contains two centrioles, duplicates during the S phase of the cell cycle, concurrent with DNA replication. This ensures that by the time the cell enters mitosis, it has two fully formed centrosomes to organize the mitotic spindle. G1 is for growth, G2 is for preparation for M phase, and M phase is for actual division.
Explanation:
Iodine atoms are incorporated into thyroxine (T₄, 4 iodine atoms) and triiodothyronine (T₃, 3 iodine atoms) synthesized by thyroid follicular cells. Iodine deficiency leads to goiter and hypothyroidism. Iron is in hemoglobin, calcium in bones, phosphorus in ATP and bones.
Explanation:
Growth hormone (somatotropin) is produced by the anterior pituitary. It promotes growth of bones, muscles, and other tissues. Deficiency causes dwarfism; excess causes gigantism or acromegaly.
Explanation:
Rhodopsin (visual purple) is a photopigment in rod cells consisting of opsin and retinal (from vitamin A). It bleaches upon absorbing light, initiating signal transduction for vision in low light. Cone cells contain iodopsin for color vision. Melanin is skin pigment, hemoglobin carries oxygen.
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