A researcher investigates potassium ion uptake by plant roots at two oxygen concentrations: 0% and 21% (normal air). Ion uptake is significantly higher at 21% oxygen. Which explanation best accounts for this?

• AOxygen directly reacts with potassium ions to help them cross the membrane
• BAerobic respiration at higher oxygen levels produces more ATP, providing more energy to power active transport of potassium ions
• CAt 21% oxygen, the concentration gradient of potassium ions is steeper, making diffusion faster
• DHigh oxygen levels increase membrane permeability, allowing more ions to enter by osmosis

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