Exchange and Transport in Plants Flashcards
What is the cross-section of a leaf?
How do gases enter and exit the leaves?
They enter through the stomata which are pores in the leaves. The opening and closing of the stomata are controlled by the guard cells.
How do guard cells control the opening and closing of the stomata?
When water enters the guard cells they become turgid which causes the stomata to open. When there is a lack of water the guard cells become flaccid which causes the stomata to close.
What is the role of the xylem?
It transports water and mineral ions upwards from the roots to the shoots.
What is the structure of the xylem?
It is a long hollow tube made up of dead cells. It contains lignin that kills the cells and makes the xylem hollow so water can flow up the plant uninterrupted.
What is the cohesion-tension theory for water transport?
Water evaporates from the leaves through transpiration. This creates tension which pulls more water up the leaf. Water molecules are cohesive so when one molecule is pulled up the other follows. A column of water moves up the xylem and water enters the stem through the roots.
What is transpiration?
The evaporation of water from a plant’s surface.
How does transpiration happen in leaves?
They evaporate off the surface or when the stomata open the water moves down a water potential gradient.
What factors affect the transpiration rate?
- Light intensity
- Temperature
- Humidity
- Wind
How does light intensity affect the rate of transpiration?
As the light intensity increases the rate of transpiration increases. This is because when there is light the stomata open to let in more carbon dioxide for photosynthesis.
How does temperature affect the rate of transpiration?
As temperature increases the rate of transpiration increases because the water molecules have more energy so they evaporate faster.
How does humidity affect the rate of transpiration?
The higher the humidity the lower the rate of transpiration. This is because the water potential gradient decreases when there is a lot of water outside the cell.
How does wind intensity affect the rate of transpiration?
As the wind intensity increases the rate of transpiration increases. This is because the wind blows water away from the stomata and that maintains a steep water potential gradient.
What is the role of the phloem?
It transports sugars up and down the plant.
What is the structure of the phloem?
The sieve tube cells form a tube that is used to transport solutes. The sieve tube cells then have companion cells which carry out respiration for the sieve tube cells to provide the energy they need to transport the solutes up and down the plant.
