Movement of substances
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Oxygen concentration is higher in the alveolar air than in the blood arriving at the lungs. What happens by diffusion?
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More oxygen moves from the alveolar air into the blood than in the reverse direction.
The net movement is from higher oxygen concentration in the alveolar air to lower concentration in the blood, down the oxygen concentration gradient.
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A membrane lets water pass but not sucrose. Water potential is higher on the left than on the right. What is the net movement?
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Water moves from left to right by osmosis.
Water moves from higher to lower water potential through the partially permeable membrane.
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A plant cell is placed in a solution with much lower water potential. Which observation indicates plasmolysis?
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The cell membrane pulls away from the cell wall.
Sufficient water loss makes the cell contents shrink and the membrane pull away from the wall.
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Glucose concentration is lower in the small intestine than inside its villus cells. How can glucose uptake into those cells continue?
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By active transport, supported by energy from respiration.
Glucose is taken up against its concentration gradient, from lower concentration in the intestine to higher concentration in the villus cells. This uptake depends on energy from respiration.
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Water and mineral ions both enter a root hair cell. Which statement is sufficient to identify active transport of the ions?
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The ions move from a lower concentration outside to a higher concentration inside.
This is movement against the ion concentration gradient across the cell membrane, requiring active transport.
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A potato piece changes from 4.00 g to 4.40 g. Which conclusion fits these measurements?
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It gained 10%, consistent with net water entry by osmosis.
(4.40 - 4.00) / 4.00 x 100 = 10%. In this investigation, the gain is interpreted mainly as water entering the cells.
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Using the carrot results above, which answer would score full marks for "Describe the trend"?
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Mass change falls from +14.0% at 0.0 mol/dm3 to -8.8% at 0.6 mol/dm3, then levels off at -12.0% to -12.4% from 0.8 to 1.0 mol/dm3.
It gives the direction, quotes values with units at both ends and describes the level-off with its figures.
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