Transport across membranes and osmosisEdexcel International A Level Biology: Flashcards

Exam questions on Transport across membranes and osmosis

1. A student places a cylinder of potato tissue in a large volume of concentrated sucrose solution. The water potential of the sucrose solution is −800 kPa and the water potential of the potato tissue is −500 kPa. The cell surface membranes of the potato cells are partially permeable.
   Explain, in terms of free water molecules, why water moves in this direction.2 marks
2. Root hair cells absorb nitrate ions from the soil. When the nitrate concentration in the soil water is higher than inside the cell, uptake is rapid. When the concentration in the soil water is lower than inside the cell, uptake still continues. When the root cells are treated with a respiratory inhibitor that stops them producing ATP, the uptake of nitrate ions at low soil concentration stops.
   Explain why the respiratory inhibitor stops the uptake of nitrate ions at low soil concentrations.2 marks
3. Pancreatic cells make the enzyme amylase, which is a large protein, and release it from the cell in vesicles. White blood cells called phagocytes take in whole bacteria. Neither amylase nor a bacterium crosses the cell surface membrane through a channel or carrier protein.
   Describe how the pancreatic cell releases amylase and how a phagocyte takes in a bacterium.3 marks