Active transport

Active transport moves substances from a more dilute solution to a more concentrated one, against the concentration gradient. It uses carrier proteins in the cell membrane and needs energy from respiration. Root hair cells take in mineral ions from the soil this way, and the gut absorbs sugar into blood that already has more sugar.

Key facts

  • Active transport moves substances from a more dilute solution to a more concentrated solution, against the concentration gradient. It needs energy from respiration. Root hair cells take in mineral ions this way, and the gut absorbs sugar into the blood.
  • Cells that do a lot of active transport, such as root hair cells, have many mitochondria to release the energy it needs.

Worked examples

Example 1

What is active transport?

  1. Active transport: the movement of substances from a more dilute solution to a more concentrated solution, using energy from respiration.

Answer: the movement of substances from a more dilute solution to a more concentrated solution, using energy from respiration

Example 2

Which process is this: the movement of substances from a more dilute solution to a more concentrated solution, using energy from respiration?

  1. Diffusion: high to low concentration. Osmosis: water through a partially permeable membrane. Active transport: low to high, using energy.
  2. So the answer is: active transport.

Answer: active transport

Example 3

Which process moves substances in this example: mineral ions moving from very dilute soil water into a root hair cell?

  1. The substance moves from a lower to a higher concentration, so energy from respiration is needed.
  2. So the answer is: active transport.

Answer: active transport

Example 4

Which process moves substances in this example: sugar moving from the gut into blood that already has a higher sugar concentration?

  1. The substance moves from a lower to a higher concentration, so energy from respiration is needed.
  2. So the answer is: active transport.

Answer: active transport

Example 5

Root hair cells take in mineral ions from the soil. Explain why they use active transport, and why they have many mitochondria.

  1. Soil water has a very low concentration of mineral ions.
  2. The cell already has a higher concentration, so the ions cannot diffuse in.
  3. Active transport moves them in, against the gradient, using energy.
  4. The energy comes from respiration in the mitochondria, so the cell has many of them.

Answer: the ions are more concentrated inside the cell than in the soil, so they must be moved against the gradient using energy from respiration, which happens in mitochondria

Example 6

A poison stops respiration in root hair cells. Why do they stop taking in mineral ions, but still take in water?

  1. Mineral ions move into the root hair cell against the concentration gradient, by active transport.
  2. Active transport needs energy from respiration, so it stops when respiration stops.
  3. Water moves in by osmosis, which needs no energy from the cell, so it carries on.

Answer: Mineral ions come in by active transport, which needs energy from respiration; water comes in by osmosis, which needs no energy.