GCSE Biology - AQA
3.2.5 - Active Transport
Sometimes, a cell needs to move a substance from an area of lower concentration to an area of higher concentration. In other words, it needs to move a substance against its concentration gradient.
For example, the diagram below shows a cell with a high concentration of glucose in its cytoplasm. It is surrounded by a solution which has a low concentration of glucose. The cell needs to take in glucose from the surrounding solution.
The glucose concentration is higher inside the cell than outside the cell. However, the cell needs to absorb glucose from its surroundings.
It a situation like this, diffusion would not benefit the cell. When substances move by diffusion, they always move down the concentration gradient. Therefore, if glucose was allowed to move through the cell membrane by diffusion, it would actually move out of the cell, towards the area of lower concentration.
Therefore, cells have an alternative way of moving substances, called active transport. Active transport moves a substance against its concentration gradient - from the area of lower concentration to the area of higher concentration.
The cell uses active transport to move glucose against its concentration gradient.
Unlike diffusion, which happens spontaneously due the random movement of particles, active transport is something that the cell has to do itself. When a cell carries out active transport it moves a substance in the opposite direction to the one it would move in if it was allowed to diffuse.
Because active transport moves substances in the opposite direction to the one they would move in spontaneously, the cell needs to use energy in order to carry it out. Cells carry out active transport using energy that has been released from food molecules through the process of respiration.
In active transport, the cell uses energy from respiration to move a substance against its concentration gradient.
Active transport is defined as follows:
Active transport is the net movement of a substance from an area of lower concentration to an area of higher concentration (against the concentration gradient), using energy from respiration.
Root hair cells are cells in the roots of plants, which absorb water and mineral ions from the soil.
Because root hair cells absorb mineral ions, they tend to end up with a high concentration of mineral ions in their cytoplasm.
On the other hand, the concentration of mineral ions in the soil tends to be much lower.
A root hair cell's cytoplasm usually has a higher mineral ion concentration than the soil around it.
Therefore, if mineral ions were allowed to simply move by diffusion, they would move out of the root hair cells and into the soil (because they would move down the concentration gradient). This would be bad for the plant because it needs mineral ions for healthy growth.
Therefore, root hair cells use active transport to force mineral ions to move against their concentration gradient - from the soil (which is the area of lower concentration) into the cytoplasm of the cells (which is the area of higher concentration).
Root hair cells use active transport to absorb mineral ions from the soil.
As an animal digests a meal, sugar molecules from the food need to be absorbed into the blood from the gut.
However, the blood has a higher sugar concentration than the gut does. Therefore, if the sugar molecules were allowed to move by diffusion, they would move out of the blood and into the gut.
Therefore, active transport is used to move sugar molecules from the gut into the blood.
Active transport is used to absorb sugar molecules from the gut into the blood stream.
Flashcards help you memorise information quickly. Copy each question onto its own flashcard and then write the answer on the other side. Testing yourself on these regularly will enable you to learn much more quickly than just reading and making notes.
What is active transport?
Give two examples of situations where active transport is used.
3.3.1 - Introduction to Exchange and Transport
3.2.4 - Beyond The Syllabus: Advanced Osmosis Information
Return to course page
Please consider donating to support Mooramo. I am one person doing this whole project on my own - including building the site, writing the content, creating illustrations and making revision resources. By making a one-time or repeating donation you will buy me time to work on Mooramo, meaning that I can get new content on here more quickly.Donate