6. Transport in Plants - xylem Flashcards
What is the function of the xylem?
Its a tissue which transports water and mineral ions in solution.
Substances move up the plant from the roots to the leaves.
What is the function of the phloem?
Its a tissue which transports organic substances like sugars in solution up and down the plant.
What are the xylem and phloem classed as?
Mass transport systems as they move substances over large distances.
What are the xylem vessels?
Part which transport water and ions.
What is the structure of the xylem vessels?
Very long, tube-structures formed from dead cells joined end to end.
No end cells.
The xylem has no end cells, what does this mean?
Water can pass through the middle easy as its uninterrupted.
How does water move up a plant and what theory is used to describe it?
Water moves up a plant against the force of gravity, from roots to leaves.
Explained by cohesion and tension theory of water transport.
Bullet point the stages in the cohesion and tension theory of water transport.
- Water enters.
- Cohesion.
- Tension.
- Water evaporates.
What happens in step one of the cohesion and tension theory of water transport.
WATER EVAPORATES.
Water evaporates from leaves at the top of the xylem, through process of transpiration.
What happens in step two of the cohesion and tension theory of water transport.
TENSION.
The previous step creates tension which pulls more water into leaf.
What happens in step three of the cohesion and tension theory of water transport.
COHESION.
Water molecules ate cohesive, so when some pulled into leaf others follow.
Meaning the whole column of water in the xylem from the leaves down to the roots, moves upwards.
What happens in step four of the cohesion and tension theory of water transport.
WATER ENTERS.
Water enters stem through roots.
As water movement up a plant increases…
Transpiration rate increases.
Define transpiration.
It is the evaporation of water from a plants surface, especially the leaves.
Water evaporates from moist cell walls and accumulates in the spaces between the cells in the leaf.
When stomata opens, it moves out of leaf down the water potential gradient.
Why does the water move down a water potential gradient?
As there is more water inside the leaf than in the air outside.
List 4 factors affecting transpiration rate?
Light intensity.
Temperature.
Humidity.
Wind.
How does LIGHT INTENSITY affect the rate of transpiration?
Lighter it is = faster transpiration rate.
Stomata opens when it gets light to let in CO2 for photosynthesis.
Stomata is closed when its dark, little transpiration.
How does TEMPERATURE affect the rate of transpiration?
Higher temperature = faster transpiration rate.
Warmer water molecules have more energy so they evaporate from the cells inside leaf faster.
Increases water potential gradient between the inside and outside of the leaf, making diffusion faster.
How does HUMIDITY affect the rate of transpiration?
Lower the humidity = faster the rate of transpiration.
Air around plant is dry, water potential gradient between leaf and air increases, increasing transpiration.
How does WIND affect the rate of transpiration?
Windier it is = faster rate of transpiration.
Lots of air movement blows away water molecules from around the stomata.
Increases water potential gradient, increases rate of transpiration.
What is a potometer?
Special piece of apparatus used to estimate transpiration rate.
What is a potometer used for?
Measuring water uptake by a plant.
Its assumed that water uptake by the plant is directly related to water loss by leaves.
Initially, why do we use the potometer under water and cut the shoot on a slant?
To prevent air from entering the xylem.
AND.
To increase surface area for water uptake.
What does the bubble movement represent when using the potometer?
An estimation of the transpiration rate.
