• Active transport is the movement of solutes such as glucose, amino acids and mineral ions;
  • From an area of their low concentration to an area of high concentration
  • It is movement against a concentration gradient and therefore energy is required
  • As such it only takes place in living organisms
  • The energy needed comes from respiration
  • Certain proteins in the cell surface membrane responsible for this movement are referred to as carrier proteins or channel proteins
  • The shape of each type of carrier protein is specific to the type of substances conveyed through it
  • It has been shown that the substance fits into a particular slot on the protein molecule,
  • As the protein changes from one form of shape to another the substance is moved across and energy is expended

Factors Affecting Active Transport                     

Availability of oxygen

  • Energy needed for active transport is provided through respiration
  • An increase in the amount of oxygen results in a higher rate of respiration
  • If a cell is deprived of oxygen active transport stops


  • Optimum temperature is required for respiration, hence for active transport
  • Very high temperatures denature respiratory enzymes
  • Very low temperatures inactivate enzymes too and active transport stops

Availability of carbohydrates

  • Carbohydrates are the main substrates for respiration
  • Increase in amount of carbohydrate results in more energy production during respiration and hence more active transport
  • Lack of carbohydrates causes active transport to stop

Metabolic poisons

  • Metabolic poisons e.g. cyanide inhibit respiration and stops active transport due to lack of energy

Role of Active Transport in Living Organisms

Processes requiring active transport:

  • Absorption of mineral salts from the soil into plant roots
  • Absorption of end products of digestion e.g. glucose and amino acids from the digestive tract into blood stream
  • Excretion of metabolic products e.g.urea from the cells
  • Re-absorption of useful substances and mineral salts back into blood capillaries from the kidney tubules
  • Sodium-pump mechanism in nerve cells
  • Re-absorption of useful materials from tissue fluid into the blood stream

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