Active transport moves ions against concentration gradients using energy

Steps:

• Compare ion concentrations: magnesium ions are higher inside the root cell (245) than outside (23), while nitrate ions are higher outside (109) than inside (23).
• Identify the process: to increase magnesium ion concentration inside, ions must move against the gradient from low to high concentration.
• Recognize the mechanism: this requires active transport, a process that uses cellular energy (ATP) to pump ions uphill.
• Conclude the need: energy is essential for active transport to accumulate minerals in cells.

Why A is correct:

• Active transport is defined as the energy-dependent movement of substances against their concentration gradient, powered by ATP hydrolysis.

Why the others are wrong:

• B: Osmosis is passive diffusion of water across membranes and requires no energy.
• C: Active transport requires energy from ATP, not water as the driving force.
• D: Osmosis involves water movement down a potential gradient but does not transport ions.

Final answer: A