Active Transport
- Diffusion and osmosis rely upon the passive (no energy is required) transport of substances down concentration gradients
- Cells also need to be able to transport substances across the cell membrane against a concentration gradient.
- This requires the input of energy (in the form of ATP) released from cellular respiration
- Active transport moves substances from a more dilute solution to a more concentrated solution
Active transport across the cell membrane involves protein carrier molecules embedded in the cell membrane
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
- Nutrients (e.g. glucose) can diffuse into the bloodstream from the small intestine (the gut)
- But this is dependent on a concentration gradient existing between the small intestine and the bloodstream
- i.e. a higher concentration of glucose in the small intestine compared to the bloodstream
- Active transport allows nutrients like glucose to be transported into the bloodstream from the small intestine even when the concentration gradient is in the wrong direction
- i.e. when the concentration of sugar molecules in the bloodstream is higher
- This is essential to stop us from starving as glucose can continuously be transported to the bloodstream
Examiner Tip
Remember - an important difference between active transport and diffusion is that active transport requires energy whereas diffusion is a passive process
