GCE AQA BIOL - Membrane transport
Unit 3.1 Biology and disease
3.1.3 Substances are exchanged between organisms and their environment by passive or active transport across exchange surfaces. The structure of plasma membranes enables control of the passage of substances across exchange surfaces.Diffusion:
There are different types of membrane transport you will need to learn for GCE AQA Biology. 😊
Diffusion is the net movement of molecules or ions from a region of a high to a low concentration until evenly distributed
There are 2 types of diffusion you should be familiar with: 1. Simple diffusion: passive (using molecules’ inherent kinetic energy), without the help of any channels or proteins
2. Facilitated diffusion: diffusion through a protein
Osmosis is the movement of water from a region of higher to lower water potential, across a partially permeable membrane.
Active transport is the movement of particles from a region of lower to higher concentration, using ATP ⚡and carrier proteins
Now that you understand the principles behind these different forms of membrane transport, we can apply them to the example of the absorption of the products of carbohydrate digestion in the small intestine. 🍞
Generally, the goal is to move the products of digestion from the lumen of the ileum into the bloodstream, where the products like glucose, amino acids, and fats can be sent to the places in the body that need it. To do so, the products need to pass through the wall of the small intestine and enter the blood. This process of absorption requires different types of membrane transport: in GCE AQA Biology, you will be asked to examine diffusion, active transport, and co-transport.
Diffusion Diffusion is from high to low concentration. Glucose can diffuse across the intestinal wall as they are very small molecules.
Active transport and co-transportHowever, as more and more glucose diffuses from the intestine to the blood, net movement of glucose stops when the concentrations on either side equalise. To absorb the rest of the glucose, we need a process known as co-transport. This requires ATP because sodium ions are first used to build up a concentration gradient via active transport, which then allows glucose to diffuse along with sodium ions, using a co-transport protein.
That's all for this article!
Wanna Boost Up Your GCE AQA Biology? Check out our study tips here!
Written by Justine | Biology Specialist @ Tuttee
ReferencesToole, G., & Toole, S. (2015). Aqa biology A level. Oxford: Oxford University Press.Images from
We just sent you an email. Please click the link in the email to confirm your subscription!