Diffusion and facilitated diffusionAQA A-Level Biology: Mind map

Exam questions on Diffusion and facilitated diffusion

1. Glucose enters red blood cells through carrier proteins in the cell-surface membrane, and no ATP is used. Oxygen also enters red blood cells, but without the help of any membrane protein. In both cases the concentration outside the cell is higher than inside.
   Describe how a carrier protein moves glucose into the cell.2 marks
2. A cell takes up substance X by facilitated diffusion through carrier proteins in its cell-surface membrane. The concentration of X outside the cell is higher than inside the cell.
   The rate of uptake of X increased as the outside concentration rose from 0 to 6 mmol dm⁻³, but stayed constant at higher concentrations. Explain why the rate stayed constant.2 marks
3. Cells lining the small intestine have microvilli, which are folds of the cell-surface membrane. A researcher compared one cell with microvilli and a similar cell without. The absorptive membrane area is 1500 µm² for the cell without microvilli and 18 000 µm² for the cell with microvilli. Both membranes have 40 carrier proteins per µm².
   Explain how the adaptations of the cell with microvilli allow rapid transport across its membrane.3 marks