Active transport – Higher tier only
Active transport is the movement of dissolved molecules into or out of a cell through the cell membrane, from a region of lower concentration to a region of higher concentration. The particles move against the The difference in the concentration of a chemical across a membrane., using energy released during The chemical change that takes place inside living cells, which uses glucose and oxygen to release the energy that organisms need to live. Carbon dioxide is a by-product of respiration..
Sometimes dissolved molecules are at a higher concentration inside the cell than outside, but because the organism needs these molecules, they still have to be absorbed. Carrier proteins pick up specific molecules and take them through the cell membrane against the concentration gradient.
Examples of active transport include:
- uptake of A simple sugar used by cells for respiration. by epithelial cells in the Finger-like projections in the small intestine that provide a large surface area for the absorption of food. of the small intestine
- uptake of ions from soil water by root hair cells in plants
Because energy is required for this process to occur, anything that prevents oxygen or glucose uptake by the cell will also prevent respiration. Without respiration, energy is not released from glucose and active transport cannot occur.
When discussing transport to get home, Alfred, the science app, tells Jamila and Megan all about active transport
Comparing diffusion, osmosis and active transport
| Diffusion | Osmosis | Active transport | |
| Down a concentration gradient | ✓ | ✓ | ✗ |
| Against a concentration gradient | ✗ | ✗ | ✓ |
| Energy needed | ✗ | ✗ | ✓ |
| Substance moved | Dissolved solutes | Water | Dissolved solutes |
| Notes | Gases and dissolved gases also diffuse | Partially permeable membrane needed | Carrier protein needed |
| Down a concentration gradient | |
|---|---|
| Diffusion | ✓ |
| Osmosis | ✓ |
| Active transport | ✗ |
| Against a concentration gradient | |
|---|---|
| Diffusion | ✗ |
| Osmosis | ✗ |
| Active transport | ✓ |
| Energy needed | |
|---|---|
| Diffusion | ✗ |
| Osmosis | ✗ |
| Active transport | ✓ |
| Substance moved | |
|---|---|
| Diffusion | Dissolved solutes |
| Osmosis | Water |
| Active transport | Dissolved solutes |
| Notes | |
|---|---|
| Diffusion | Gases and dissolved gases also diffuse |
| Osmosis | Partially permeable membrane needed |
| Active transport | Carrier protein needed |
