Edexcel IGCSE Biology 复习笔记 2.4.5 Active Transport

• Active transport is:

The movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration using energy from respiration

• 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 across the cell membrane involves protein carrier molecules embedded in the cell membrane

Active transport across the cell membrane - the molecules here are being transported against the concentration gradient, from a region of lower concentration (outside the cell) to a region of higher concentration (inside the cell)

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 molecules 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
• The active uptake of glucose by epithelial cells in kidney tubules in the kidney nephron allows for the reabsorption of glucose back into the blood so that none is lost in the urine
• Sugar molecules are used in respiration to release energy for cells to function

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
  • Magnesium ions are required to make chlorophyll
  • Nitrate ions are needed to make amino acids for protein synthesis (and subsequently growth)

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