3.2.3 Transport across cell membranes - active transport and co-transport in the ileum

Active transport

• It uses energy to move molecules and ions across plasma membranes against a concentration gradient

• Carrier proteins and co-transporters are involved

Carrier proteins

• A molecule attaches to the carrier protein, the protein changes shape and this moves the molecule across the membrane, releasing it on the other side

What are the differences between facilitated diffusion and active transport?

• Active transport usually moves solutes from a low to a high concentration, in facilitated diffusion they always move from a high to a low concentration

• Active transport requires energy, facilitated diffusion does not

Why is ATP important for active transport?

• ATP undergoes a hydrolysis reaction, splitting into ADP and Pi

• This releases energy so that the solutes can be transported

Co-transporters

• They are a type of carrier protein

• They bind two molecules at a time

• The concentration gradient of one of the molecules is used to move the other molecule against its own concentration gradient

• Sodium ions move across the membrane down their concentration gradient. This moves glucose across the membrane too, against its concentration gradient

Co-transport and the absorption of glucose

• Glucose is absorbed into the bloodstream in the small intestine

• In the mammalian ileum (the final part of a mammal’s small intestine), the concentration of glucose is too low for glucose to diffuse out into the blood

• So glucose is absorbed from the lumen (middle) of the ileum by co-transport