Transport in Plants Flashcards
Describe the role of xylem in plants.
The xylem transports water and solutes from the roots to the leaves. It is also used to replace water lost during transpiration and photosynthesis. When water evaporates out of the leaves, the water potential in the mesophyll cells becomes lower than the water potential in the xylem, which creates a pulling force which draws water out from the xylem vessels into the mesophyll cells. This called the transpiration pull.
Explain how water is absorbed by root hair cells.
Water is absorbed from the soil by osmosis. Root hair cells are adapted for this by having a large surface area to speed up osmosis.
Define transpiration.
Transpiration is the process by which water moves up the plant against gravity from the roots to the stomata where it evaporates out of the leaves.
Explain how humidity affects the rate of transpiration.
When the air around the plant is humid, this reduces the diffusion gradient between the air spaces in the leaf and the external air. The rate of transpiration therefore decreases in humid air and speeds up in dry air.
Explain how wind speed affects the rate of transpiration.
The rate of transpiration increases with faster air movements across the surface of the leaf. The moving air removes any water vapour which might remain near the stomata. The moist air would otherwise reduce the diffusion gradient and slow down diffusion.
Explain how temperature affects the rate of transpiration.
High temperatures increase the rate of transpiration, by increasing the rate of evaporation of water from the mesophyll cells.
Explain how light intensity affects the rate of transpiration.
The rate of transpiration increases in the light, because of the opening of the stomata in the leaves.
Describe how you would investigate the effect of light intensity on the rate of transpiration.
You can measure the rate of transpiration of a plant by measuring how quickly it produces oxygen using an aquatic plant such as a pondweed placed upside down in a test tube in a beaker of water. The light intensity is changed by moving the lamp, altering the distance between the lamp and the pondweed. The beaker of water keeps the temperature of the plant constant. The bubbles produced by the plant per minute is a measure of the rate of transpiration of the plant.
Describe the role of phloem in plants.
The phloem is a living tissue that transports products of photosynthesis, in particular, sucrose, to other parts of the plant. Sucrose is loaded into the phloem via active transport. This causes water from the xylem to move into the phloem by osmosis creating pressure that pushes the sucrose down the tube.
