NEET 2020 Botany Question 15 Solution

The proximal convoluted tubule (PCT) of the renal nephron performs the bulk of tubular reabsorption: - Approximately 70–80% of filtered water, electrolytes ($Na^+$, $K^+$, $Cl^-$, $HCO_3^-$), and virtually 100% of essential nutrients (glucose, amino acids) are actively and passively reabsorbed here. - To support this massive transport load, the PCT is lined by simple cuboidal epithelial cells featuring a densely packed apical array of finger-like projections called microvilli (brush border). - This brush border increases the luminal absorptive surface area more than 20-fold. The basolateral membranes are deeply invaginated and packed with abundant mitochondria to power $Na^+/K^+$ ATPase pumps.

- Lining of intestine: Lined by simple columnar epithelium with microvilli and goblet cells, not cuboidal. - Ducts of salivary glands: Lined by simple cuboidal/columnar or compound stratified epithelium without an apical brush border. - Eustachian tube: Lined by ciliated pseudostratified columnar epithelium.