Co-transport and Active Transport in A-level Biology
Active Transport Process
Active transport is a vital cellular process that moves molecules against their concentration gradient, requiring energy in the form of ATP. The process involves carrier proteins spanning the cell membrane.
- The molecule to be transported binds to a receptor on the carrier protein.
- ATP binds to the carrier protein from inside the cell and is hydrolyzed into ADP and Pi.
- This hydrolysis causes the carrier protein to change shape, releasing the molecule on the other side of the membrane.
- The phosphate ion is then released, and the protein returns to its original shape.
Definition: Active transport is the movement of molecules across a cell membrane against their concentration gradient, requiring energy in the form of ATP.
Co-transport of Glucose and Sodium Ions in the Ileum
The ileum, part of the small intestine, uses co-transport to absorb glucose from the lumen into epithelial cells and then into the bloodstream.
Highlight: Co-transport of glucose and sodium ions is crucial for nutrient absorption in the small intestine, particularly in the ileum.
This process is necessary because:
- Glucose absorption requires a higher concentration of glucose in the lumen compared to the epithelial cell for facilitated diffusion.
- Usually, there is more glucose in the epithelial cells than in the lumen.
- Active transport and co-transport are required to overcome this concentration gradient.
Example: In the co-transport of sodium and glucose A-level Biology, sodium ions are actively transported out of the epithelial cell into the blood, creating a concentration gradient that drives the absorption of glucose.
Vocabulary: Lumen refers to the inner space of a tubular structure, such as the intestine.
