The part of the nephron that creates a concentration gradient in the kidney medulla is:
A. Loop of Henle
B. Bowman's capsule
C. Proximal convoluted tubule
D. Distal convoluted tubule
Answer: Option A
Solution (By JKExamLibrary)
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:
Smooth endoplasmic reticulum (SER) lacks ribosomes and is involved in lipid and steroid hormone synthesis, carbohydrate metabolism, and detoxification of drugs and poisons (via cytochrome P450 enzymes). Rough ER synthesizes proteins. Golgi modifies/packages. Lysosomes digest. Liver cells have abundant SER. SER also sequesters Ca²⁺ ions in muscle cells (sarcoplasmic reticulum).
Explanation:
Human somatic cells have 46 chromosomes: 44 autosomes and 2 sex chromosomes (XX or XY). Sperm cells are haploid (n=23), containing 22 autosomes and one sex chromosome (either X or Y). The ovum also has 22 autosomes and one X. Fertilization restores 44 autosomes plus XX or XY. So sperm has 22 autosomes.
Explanation:
Crossing over, the exchange of genetic material between non-sister chromatids of homologous chromosomes, occurs during the pachytene stage of prophase I. The synaptonemal complex facilitates this. Chiasmata become visible in diplotene when the synaptonemal complex dissolves. Leptotene is chromosome condensation, zygotene is synapsis. This process is crucial for genetic variation.
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