CIE IGCSE Biology: 复习笔记：3.1.8 Proteins & Active Transport

• Energy is needed because particles are being moved against a concentration gradient, in the opposite direction from which they would naturally move (by diffusion)
• Active transport is vital process for the movement of molecules or ions across membranes
• Including:
  • uptake of glucose by epithelial cells in the villi of the small intestine and by kidney tubules in the nephron
  • uptake of ions from soil water by root hair cells in plants

• Active transport works by using carrier proteins embedded in the cell membrane to pick up specific molecules and take them through the cell membrane against their concentration gradient:

1. 1. Substance combines with carrier protein molecule in the cell membrane
   2. Carrier transports substances across membrane using energy from respiration to give them the kinetic energy needed to change shape and move the substance through the cell membrane
   3. Substance released into cell

Carrier proteins in active transport.