Active transport requires movement against concentration gradients

Steps:

• Compare particle concentrations between cells to identify gradients.
• Active transport moves particles from low to high concentration; passive transport moves from high to low.
• Check each option's direction against the table's gradients.
• Select the option where movement opposes the gradient.

Why B is correct:

• Oxygen concentration is higher in cell 1 than cell 2, so moving oxygen from cell 2 (low) to cell 1 (high) is against the gradient, requiring energy per active transport definition.

Why the others are wrong:

• A: Nitrate ions are lower in cell 1 than cell 2, so movement from cell 2 to cell 1 follows the gradient via passive transport.
• C: Water moves from cell 1 (higher water potential) to cell 2 via osmosis, a passive process.
• D: Water moves from cell 2 (higher water potential) to cell 1 via osmosis, a passive process.

Final answer: B