(Note The overseas examination boards bear no responsibility for the suggested answers contained in this publication. Answers for HKCEE and HKALE questions are not available due to copyright restrictions.) Ch 3
Movement of substances across cell membrane Exercise Multiple-choice questions (p. 3-25) 1
C Short questions (p. 3-27) 12
HKALE Biology 2006 I Q9 13
Passive / do not require energy or ATP
Movement down a concentration gradient / by diffusion
It occurs only when oxygen is present because energy / respiration is required.
There is no uptake in curve Z.
The concentration inside cells is higher than surrounding solution.
Diffusion is proportional to the concentration gradient.
Water has a higher water potential than the cell contents. It moves across the differentially permeable membrane into the cells by osmosis.
As the cell membranes of red blood cells are thin and not surrounded by cell walls, the cells burst when more and more water enters. Therefore no blood cells can be observed under the microscope.
Distilled water has a higher water potential than potato.
Therefore in distilled water, water moves into potato by osmosis.
Concentrated sugar solution has a lower water potential than potato.
Therefore in concentrated sugar solution, water moves out of potato.
Potato in distilled water becomes heavier than the one in concentrated sugar solution.
Any two from
1m x 2
The vacuoles of the cells in distilled water are bigger than the ones in sugar solution.
The cell membranes are pulled away from the cell walls in the cells in sugar solution / cells in sugar become flaccid / cells become plasmolysed.
Contents of the cells push against the cell walls in the cells in distilled water / cells in distilled water become turgid.
HKALE Biology 1998 I Q4 17
III should show two arms of membrane surrounding...
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