A-LevelBiologyCell membranes and transport9700/12 · Feb/Mar 2019 · Q131 Mark
An investigation was carried out into the effect of different treatments on the permeability of the cell surface membranes and tonoplasts of beetroot cells. Beetroot cell vacuoles contain a red pigment. This pigment is unable to pass out of the cells because it cannot diffuse through the tonoplasts or cell surface membranes. 1 cm³ cubes were cut from beetroot tissue and washed in running water for 20 minutes to remove any pigment released from damaged cells. The cubes were then placed in test-tubes with different contents and observed for five minutes. Which row shows a correct explanation for the observation recorded for one of the treatments?
Atreatment: dilute hydrochloric acid, observation: contents of test-tube stay clear, explanation: membrane proteins have been denatured
Btreatment: ethanol, observation: contents of test-tube turn red, explanation: lipids, including membrane phospholipids, have dissolved
Ctreatment: water at 20°C, observation: contents of test-tube stay clear, explanation: membrane proteins have been denatured
Dtreatment: water at 80 °C, observation: contents of test-tube turn red, explanation: lipids, including membrane phospholipids, have dissolved
✓ Correct answer
B: treatment: ethanol, observation: contents of test-tube turn red, explanation: lipids, including membrane phospholipids, have dissolved
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