Active Transport in Nutrient Uptake

Steps:

• Recall active transport moves substances against concentration gradients using energy (ATP).
• Evaluate each option: identify if uptake requires energy or occurs passively.
• In villi cells, check intestinal absorption mechanisms for gases, sugars, and polymers.
• For root cells, assess water movement via osmosis versus active processes.

Why B is correct:

• Glucose uptake by villi cells uses sodium-glucose cotransporters (SGLT1), an active process requiring ATP to move glucose against its gradient.

Why the others are wrong:

• A: Oxygen uptake by villi cells occurs via passive diffusion down its concentration gradient.
• C: Starch is not directly absorbed; it is hydrolyzed to glucose/maltose, which then uses active or facilitated transport.
• D: Water uptake by root cells happens by osmosis, a passive process following the water potential gradient.

Final answer: B