Active transport causes divergence in transport curves against gradients

Steps:

• Examine the two curves for differences in substance accumulation over time.
• Identify if one curve plateaus at equilibrium while the other continues rising.
• Recognize that rising beyond equilibrium requires energy-dependent movement.
• Determine active transport as the process enabling against-gradient transport.

Why A is correct:

• Active transport uses ATP energy to move substances against their concentration gradient, allowing accumulation higher than diffusion equilibrium, as per the definition of carrier-mediated transport.

Why the others are wrong:

• B. Diffusion is passive movement down the gradient, reaching equilibrium without energy, so it cannot explain divergence.
• C. Osmosis involves water movement across membranes down its gradient, not solute curves.
• D. Photosynthesis converts light energy to chemical energy in chloroplasts, unrelated to membrane transport curves.

Final answer: A