4.2.3 Active Transport

• Active transport is the movement of molecules and ions through a cell membrane from a region of lower concentration to a region of higher concentration using energy from respiration
• Active transport requires carrier proteins (each carrier protein being specific for a particular type of molecule or ion)
• Although facilitated diffusion also uses carrier protein, active transport is different as it requires energy
• The energy is required to make the carrier protein change shape, allowing it to transfer the molecules or ions across the cell membrane
• The energy required is provided by ATP (adenosine triphosphate) produced during respiration

A carrier protein changing shape during active transport

• Active transport is important in:
  • Reabsorption of useful molecules and ions into the blood after filtration into the kidney tubules
  • Absorption of some products of digestion from the digestive tract
  • Loading sugar from the photosynthesising cells of leaves into the phloem tissue for transport around the plant
  • Loading inorganic ions from the soil into root hairs