Active Transport

Active transport moves molecules against the concentration gradient. This means it works in the opposite direction to diffusion.

Because active transport fights against the natural flow, it must move substances from where they are less concentrated to where they are more concentrated — that is, from low to high concentration.

The correct answer is from a region of low concentration to a region of high concentration. The other options describe diffusion or osmosis, not active transport.

The question asks about the direction of movement in active transport specifically. We need to find the option that correctly describes movement against the concentration gradient.

'From high to low concentration' describes diffusion, not active transport. This is the most common misconception and is therefore incorrect here.

'High water potential to low water potential' and 'low water potential to high water potential' both describe osmosis, which involves the movement of water molecules only. These do not apply to active transport.

The only remaining option — from low to high concentration — correctly describes active transport moving molecules against their concentration gradient.

The nitrate concentration is higher inside the cell than in the soil. This means the ions are being moved from low concentration (soil) to high concentration (inside the cell).

Diffusion and facilitated diffusion both move substances down the concentration gradient (high to low), so they cannot explain movement from the soil into an already more concentrated cell. Osmosis only involves water.

Active transport is the only process that moves substances against a concentration gradient, using ATP energy and carrier proteins. This matches exactly what is described.

The question tells us nitrate concentration is higher inside the cell than in the soil — so the ions are moving from low to high concentration. Any correct answer must explain how this happens.

Osmosis involves the movement of water molecules only, not mineral ions. This option is irrelevant to nitrate ion uptake.

Diffusion moves substances from high to low concentration. Since the concentration is already higher inside the cell, diffusion would actually move nitrate ions out of the cell, not in.

Facilitated diffusion also moves substances down the concentration gradient — it just uses channel proteins to help. It still cannot move ions from low to high concentration.

Active transport is the only process that moves substances against the concentration gradient using energy (ATP). This is the correct answer.