Water enters root cells by osmosis down a water potential gradient

Steps:

• Soil water has higher water potential than root cells due to dissolved solutes in cells lowering their potential.
• Water moves passively across cell membranes from higher to lower water potential.
• This process is osmosis, requiring no energy input.
• Active transport of ions maintains the gradient but does not directly move water.

Why A is correct:

• Osmosis defines water movement across semi-permeable membranes from high to low water potential, as per the water potential gradient law (ψ = ψ_s + ψ_p).

Why the others are wrong:

• B: Water movement is passive via osmosis, not active transport, which requires energy for solutes against gradients.
• C: Identical to B; water does not move from low to high potential.
• D: Osmosis occurs down the gradient (high to low), not against it.

Final answer: A