The oxygen produced by a plant comes most directly from

Choice A rationale: Cell membranes pressed tightly against the cell walls is correct because this is what happens when a plant cell is placed in a hypotonic solution. A hypotonic solution has a higher concentration of water than the cell, so water moves into the cell and out of the solution by osmosis, causing the cell to swell and press against the cell wall. This is called turgor and it helps the cell maintain its shape and rigidity.

Choice B rationale: Many of the cells had burst is incorrect because plant cells do not burst in a hypotonic solution, unlike animal cells. Plant cells have a rigid cell wall that prevents them from bursting, even when they are full of water. The cell wall can withstand the pressure of water entering the cell.

Choice C rationale: Full central vacuoles is correct because this is also what happens when a plant cell is placed in a hypotonic solution. The central vacuole is a large organelle that stores water and other substances in the plant cell. When water enters the cell, the central vacuole expands and fills up the cell, increasing its turgor pressure.

Choice D rationale: Many of the cells had become crenated is incorrect because crenation is the opposite of what happens in a hypotonic solution. Crenation is the process by which a cell shrinks and becomes wrinkled due to water loss in a hypertonic solution. A hypertonic solution has a lower concentration of water than the cell, so water moves out of the cell and into the solution by osmosis, causing the cell to shrink.

Choice A rationale: An isotonic solution has the same solute concentration as the plant cells, which means it has the same water potential. Water will move in and out of the plant cells at the same rate, causing them to remain unchanged in size and shape. This will not help the lettuce to become less wilted.

Choice B rationale: A hypertonic solution has a higher solute concentration than the plant cells, which means it has a lower water potential. Water will move out of the plant cells by osmosis, causing them to shrink and become plasmolysed. This will make the lettuce more wilted and not crisper.

Choice C rationale: Soaking the lettuce in water would have an effect, depending on the relative solute concentration of the water and the plant cells. Water will move across the cell membrane by osmosis, either into or out of the plant cells, causing them to change in size and shape.

Choice D rationale: A hypotonic solution has a lower solute concentration than the plant cells, which means it has a higher water potential. Water will move into the plant cells by osmosis, causing them to swell and become turgid. This will make the lettuce crisper and more appealing.

Choice E rationale: A hypotonic solution will cause the plant cells to gain water and become turgid, not more wilted. Wilted lettuce is caused by the loss of water from the plant cells, which makes them flaccid and soft.