Oxygen limits active transport in roots

Steps:

• Root hairs absorb water via osmosis and ions like nitrate via active transport.
• Osmosis is passive, driven by water potential gradients, not requiring energy.
• Active transport of nitrate ions uses ATP from aerobic respiration.
• Waterlogged soil lacks oxygen, halting respiration and ATP production, slowing active transport but not osmosis.

Why B is correct:

• Nitrate uptake relies on active transport powered by ATP from oxygen-dependent respiration; water uptake is passive osmosis, unaffected by oxygen lack.

Why the others are wrong:

• A: Water uptake unaffected, as osmosis does not require oxygen.
• C: Nitrate uptake slowed, as it depends on energy from respiration.
• D: Nitrate uptake slowed by oxygen deficiency impacting active transport.

Final answer: B