The gametes in humans are haploid, containing how many chromosomes?
A. 22
B. 23
C. 46
D. 44
Answer: Option B
Solution (By JKSSB Mock Tests)
Human somatic cells are diploid (2n = 46), with 23 pairs of homologous chromosomes. Gametes (sperm and egg) are haploid (n = 23), containing one set of chromosomes. Fertilization restores diploidy. The haploid number is 23. Option 22 would be autosomes plus one sex chromosome, but the total count is 23. 44 is the number of autosomes in somatic cells.
Assertion (A): Genetic variation is essential for evolution.
Reason (R): Without variation, natural selection cannot occur because there are no differences to select from.
A.Both A and R are true, and R is the correct explanation.
B.Both A and R are true, but R is not the correct explanation.
Explanation:
Genetic variation provides the raw material for natural selection. If all individuals were identical, selection could not favor any. R correctly explains A.
Explanation:
The loop of Henle, especially the descending limb (permeable to water) and ascending limb (impermeable, active salt transport), creates an osmotic gradient in the medulla. This countercurrent multiplier system enables the kidney to produce concentrated or dilute urine depending on hydration status. ADH acts on the collecting duct to utilize this gradient.
Explanation:
The Glomerular Filtration Rate (GFR) is the volume of fluid filtered from the renal glomerular capillaries into the Bowman's capsule per unit time. In a healthy adult, the normal GFR is approximately 125 ml per minute, which amounts to about 180 liters per day. Almost all of this filtrate is reabsorbed, leaving only 1.5 liters of urine.
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