Cells: Transport across cell membranes

A student placed potato cylinders in sucrose solutions and recorded the percentage change in mass (Figure 2). Use Figure 2 to estimate the water potential of the potato tissue as a sucrose concentration, and explain how you used the graph.

Explain why the student calculated percentage change in mass rather than change in mass.

Explain why the cell-surface membrane is described as a fluid mosaic.

Describe and explain how the structure of the plasma membrane, and of the cells lining the ileum, allow glucose to be absorbed into the blood. (Level of response: 6 marks for the description, plus 4 marks for explanation and use of terminology.)

Give two differences between facilitated diffusion and active transport.

Cyanide stops respiration. Explain the effect of cyanide on the uptake of mineral ions by root hair cells.

Explain how amino acids are absorbed from the ileum into the blood.

Investigation (written for this paper): beetroot discs of equal size were washed and placed in water at different temperatures for 30 minutes. The absorbance of the water was measured with a colorimeter.

Temperature / °C	20	40	60	80
Mean absorbance	0.08	0.12	0.54	0.91

Explain why the discs were cut to the same size and washed before the experiment.

Explain the results between 40 °C and 80 °C.

Write an essay on ONE of the following topics. EITHER The importance of membranes in living organisms. OR The ways in which organisms use energy released from ATP. You should select and use information from different parts of the specification.

Explain how the structure of a channel protein allows facilitated diffusion of ions.

Plant cells with a water potential of −600 kPa are placed in a solution with a water potential of −400 kPa. Explain what happens.