ACTIVE TRANSPORT
- 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
Temperature
- 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