AP BIOLOGY

Detailed explanation-1: -Selective reabsorption is the process whereby certain molecules (e.g. ions, glucose and amino acids), after being filtered out of the capillaries along with nitrogenous waste products (i.e. urea) and water in the glomerulus, are reabsorbed from the filtrate as they pass through the nephron.

Detailed explanation-2: -Substances like glucose, amino acids, Na+, are reabsorbed by active transport whereas the nitrogenous wastes and water are reabsorbed passively.

Detailed explanation-3: -Glucose, amino acids, and salts can be reabsorbed against a concentration gradient and their transport across the nephron into the capillaries requires energy (see active transport).

Detailed explanation-4: -So the correct option is ‘Active Transport’.

Detailed explanation-5: -Glucose is reabsorbed by active transport and PAH is secreted by active transport. Active transport is an enzyme dependent process. (transporters are enzymes). All enzyme-mediated processes are saturable.