Active vs. Passive Absorption in Living vs. Dead Tissue

Steps:

• Active transport requires energy from living cells and stops in dead tissue; diffusion occurs passively in both.
• Arabinose shows identical absorption rates (31) in living and dead intestines, indicating no energy dependence.
• Glucose shows a much higher rate in living (102) vs. dead (34) intestines, indicating energy-dependent active transport.
• Thus, arabinose absorbs by diffusion, while glucose uses active transport.

Why B is correct:

• B aligns with the definition of active transport (higher rate only in living tissue due to energy use) and diffusion (unchanged rate in dead tissue).

Why the others are wrong:

• A: Arabinose rate unchanged in dead tissue, ruling out active transport.
• C: Glucose rate drops sharply in dead tissue, requiring active transport; arabinose fits diffusion, not active.
• D: Glucose's elevated living rate exceeds what diffusion alone predicts.

Final answer: B