Active transport (AQA GCSE Combined Science: Trilogy: Biology): Revision Note

Principles of active transport

• During diffusion, substances move down a concentration gradient, from a higher to a lower concentration; during osmosis, water moves from a dilute solution to a more concentrated solution

• However, cells also need to transport substances across the cell membrane against a concentration gradient; this is known as active transport

  • Substances move from low to high concentration

  • This requires energy, released by (aerobic) respiration in the mitochondria; cells that carry out a lot of active transport (e.g. root hair cells, cells lining the villi) contain many mitochondria

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Active transport: Examples

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