Ion Absorption Mechanisms in Plants

Steps:

• Examine concentration gradient at point N: higher inside plant than outside, requiring energy.
• Confirm active transport at N uses ATP to move Mg²⁺ against gradient.
• Check gradient at point P: higher outside, allowing passive movement.
• Verify diffusion at P occurs without energy down the gradient.

Why B is correct:

• Active transport moves ions against concentration gradient (as at N), while diffusion follows it (as at P), per Fick's law of diffusion.

Why the others are wrong:

• A: Ignores diffusion at P where gradient favors passive uptake.
• C: Reverses mechanisms; N requires active due to opposing gradient.
• D: Fails to account for active needs at N against gradient.

Final answer: B