Active Transport

In the examples we looked at previously, substances are transported passively, down concentration gradients.

Sometimes, substances have to be moved from a low to a high concentration - against a concentration gradient.

Active transport is a process that is required to move molecules against a concentration gradient. This process does require energy.

For plants to take up mineral ions, ions are moved into root hair cells, where they are in a higher concentration than in the soil.

Active transport occurs within the root so that the plant takes in even more of the ions that it needs from the soil.

In animals, glucose molecules have to be moved across the gut wall into the blood. The glucose molecules in the intestine might be in a higher concentration than in the intestinal cells and blood – for instance, after a meal.

However, all of the glucose in the gut needs to be absorbed.

When the glucose concentration in the intestine is lower than in the intestinal cells, movement of glucose involves active transport. The process requires energy produced by respiration.