Question

On a sunny day at an open market a vendor, Ms Milly, occasionally sprinkles water on her wilting lettuce. During the day Ms Milly’s lettuce are firm and ready for sale. (i) Distinguish between “diffusion’’ and “osmosis”. (2 mark) (ii) Identify the process that resulted in Ms Milly’s wilting lettuce becoming firm. (1 mark) (iii) Explain how the process identified in (b) (ii) kept the lettuce firm. (2marks) (iv) Suggest a suitable method, other than sprinkling, that a consumer could use to keep the lettuce firm.

Answer 1

The net movements of molecules of gasses and particles from a region of higher concentration to the region of lower concentration based on diffusion gradients  without a separating medium is called Diffusion.

Osmosis is the movement of water molecules from the region from a region of higher water  potential to that of lower water potential across a separating medium of semipermeable membrane.

Because of exposure of the lettuce to sunlight, there is rapid diffusion of water  molecules from the cells of the lettuce on the sunny day than into the cells from the environment. Because the turgor pressure has dropped to zero, so water molecules diffuse from the region of higher water potential (the cells of the lettuce) to region of lower (sounding air). This results to shrinking of the cells, called witting.

However, as she waters the lettuce, water molecules diffuses into   the cell and move up the cells through osmosis, the  water  molecules makes the lettuce cells turgid. The turgor pressure has returned to normal . This  explains the firmness.

Water diffuses into the vacuole which has capacity to store water. The presence of water increases vacuole's volume which expands through osmosis, and therefore changes it shape. The changes in shape leads to firmness.

Ms. Milly can keep the stalk of the lettuce in flower pot filled with water. The  continues to keep the cells of the lettuce turgid, by replacing the lost water  through diffusion into the sunny environment to prevent wilting,

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