co transport 4.5

how do we increase the rate of movement across-membranes? 3 ways

The epithelial cells are lined with microvilli which provide a large surface area

also increase the density of protein channels/carrier proteins

-by increasing the concentration gradient

Role of diffusion in absorption: ?

- There is usually a higher concentration of glucose and amino acids in the ileum than the blood.

Due to blood always circulating, glucose is always being used up by cells for respiration.

This helps maintain the concentration gradient between the ileum and the blood meaning the rate of movement by facilitated diffusion and is increased.

Role of active transport in absorption:
why cannot simple diffusion work?

Simple diffusion results in an equilibrium between the ileum and the blood so the glucose and amino acids that should be in the blood aren’t being absorbed.


Through co-transport glucose and amino acids diffuse into the blood with sodium ions that have been transported by the sodium potassium pump.

Explain the process of co-transport? 5 steps

1)sodium ions are actively transported out of the epithelial cells, by the sodium potassium pump into the blood.

2) This maintains a higher concentration of sodium ions in the intestine than inside epithelial cells.

3)sodium ions can now diffuse from the lumen down their concentration gradient into the epithelial cell.

4)the protein the sodium ions diffuse through is a co-transporter protein, so either glucose /amino acids attach and are transported into the epithelial cells against their concentration gradient.

5) glucose then moves by facilitated diffusion from the epithelial cells into the blood

What maintains the concentration gradient?

The concentration of glucose in the blood is lower than in the epithelial cells because the blood flows and carries away absorbed glucose.