Kidney is made up of individual units called:

Correct option is A

Correct Answer: (a) Nephrons
Explanation:
→ Nephrons are the functional units of the kidney responsible for filtration, reabsorption, and excretion.
→ Marine and freshwater fishes differ in nephron structure based on osmoregulatory needs.
Information Booster:
→ Glomerular size varies with habitat salinity.
→ Each nephron contains glomerulus, tubules, and collecting ducts.
→ Critical for ionic balance and waste removal.
Additional Information (Other Options):
(b) Neurons – nervous system.
(c) Ganglia – nerve cell clusters.
(d) Glomeruli – part of nephron, not whole.