Active transport (AQA GCSE Biology: Combined Science)

• Diffusion and osmosis rely upon the passive transport of substances down concentration gradients, relying on the random movement of particles
• However, cells also need to be able to transport substances across the cell membrane against a concentration gradient. This requires energy released by respiration
  • The energy from respiration is used by protein transport molecules embedded in the cell membrane to move substances into or out of the cell

• Active transport moves substances from a more dilute solution to a more concentrated solution

Active transport across the cell membrane involves protein carrier molecules embedded in the cell membrane

Plants

• Root hair cells lining the surface of plant roots need to move minerals such as magnesium ions from a region of lower concentration (the very dilute solution of minerals in the soil surrounding the roots) to a region of higher concentration (inside the cytoplasm of the cell)
• Mineral ions are needed by plants to function healthily
  • Magnesium ions are needed to make chlorophyll
  • Nitrate ions are needed to make amino acids and therefore for protein synthesis (and subsequently growth)

Animals

• Food molecules (such as the sugar glucose) can be absorbed across the wall of the small intestine by diffusion, but this is dependent on a concentration gradient existing between the lumen of the intestine and the bloodstream
• Active transport allows sugar such as glucose to be transported into the bloodstream from the lumen of the small intestine (the gut) when the concentration of sugar molecules in the blood is higher
  • Sugar molecules are used in respiration to release energy for cells to function