A membrane exchanger has a concentrated urea solution flowing along one side of a membrane and water flowing along the other side. At first, the liquids flow at the same speed in opposite directions.
The direction of the water flow is reversed so that both liquids flow in the same direction. The flow speeds, temperature and membrane surface area do not change.
How will changing the water flow affect the transfer of urea across the membrane?
The transfer rate will decrease because the concentration difference falls as the liquids flow alongside each other.
The transfer rate will remain unchanged because the incoming liquids still begin with the same concentrations.
The transfer rate will increase because urea and water particles now move in the same overall direction.
Urea will transfer back into the concentrated solution near the outlet because the water has gained urea.
140 exam-style questions on AQA GCSE Biology 1.3 Transport in cells, covering 1.3.1 Diffusion, 1.3.2 Osmosis, and 1.3.3 Active transport. Each one has a worked solution and a mark scheme showing where the marks go.