Question

Reabsorption of water through the tubules occurs by a. osmosis. b. active transport. c. facilitated diffusion. d. all of these.

Short answer

The short answer is: Reabsorption of water through the tubules occurs by osmosis.

Step-by-step solution

Understand osmosis

Osmosis is the movement of water molecules across a selectively permeable membrane from an area of low solute concentration to an area of high solute concentration. This process occurs until the concentrations of solutes are equal on both sides of the membrane. Osmosis is a passive process, meaning it does not require any energy input.

Understand active transport

Active transport is the movement of molecules or ions against a concentration gradient, from an area of low concentration to an area of high concentration. This process requires energy, typically in the form of ATP. Active transport usually occurs with the help of specific carrier proteins.

Understand facilitated diffusion

Facilitated diffusion is a passive transport process where molecules move across a membrane with the help of carrier or channel proteins. Unlike active transport, facilitated diffusion does not require energy input. Instead, molecules move along their concentration gradient, from an area of high concentration to an area of low concentration.

Apply knowledge of processes to reabsorption of water through the tubules

When reabsorbing water through the tubules in the kidneys, the objective is to maintain the body's water balance and concentrate the urine. This process primarily occurs through osmosis, as water moves passively from an area of low solute concentration in the tubules to an area of higher solute concentration in the interstitial fluid and bloodstream. Active transport and facilitated diffusion are involved in the reabsorption of other solutes, such as sodium, glucose, and amino acids, but not in the direct reabsorption of water.

Choose the correct answer

Based on the understanding of the processes, reabsorption of water through the tubules occurs by: a. osmosis.