AP BIOLOGY

Detailed explanation-1: -Transpiration is the loss of water vapour from the stomata of the leaves and so cannot be measured directly. Instead we assume that the water taken up by the plant is equal to the water lost and, the rate of the movement of the air bubble gives an indication of the amount of water being lost from the plant.

Detailed explanation-2: -A simple potometer is a piece of capillary tubing to which a plant has been connected. The water uptake is measured by recording the time taken for a bubble in the tube to move a set distance.

Detailed explanation-3: -The potometer does not measure the rate of transpiration accurately because not all of the water that is taken by the plant is used for transpiration (water taken might be used for photosynthesis or by the cells to maintain turgidity). The potometer measures the rate of uptake of water.

Detailed explanation-4: -A potometer measures the rate of transpiration by taking note of the change in volume per unit time. A potometer is a device which places a body of water with known volume in contact with a plants roots.