Active Transport and Co-Transport

Active transport

• The movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration using ATP and carrier proteins

• Requires carrier proteins (each carrier protein being specific for a particular type of molecule or ion)

• 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. The ATP is hydrolysed to release energy

Role of Active Transport

• Reabsorbtion of useful molecules and ions into the blood after filteration 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

Co-Transport

• Uses ions to move substances into and out of cells

• This occurs particularly in the epithelial cells of the ileum

• Na⁺ and K⁺ are pumped out of the epithelial cell by active transport into the blood leaving a lower concentration in the cell

• This causes these ions to move in from the lumen by facilitated diffusion, which at the same time brings glucose and amino acids into the cell

• These then diffuse from a high concentration in the epithelial cell to a low concentration in the blood

Co-Transport Diagram

The epithelial cells that line the small intestine are adapted for the absorption of glucose. Explain how. (6 marks)