Trasport in Plants II Flashcards
What does xylem tissue do?
Transport water and mineral ions in solution.
Move up the plant from roots -> leaves.
What does phloem tissue do?
Transport organic substances eg sugar, both up and down the plant.
Outline the structure of xylem.
- very long tube like structures formed from dead cells joined end to end.
- no end walls, making an uninterrupted tube that allows water to pass up through the middle easily.
Outline the cohesion tension theory in helping water move up plants.
- water evaporates from leaves at top of xylem (transpiration).
- this creates tension, which pulls more water up the leaf.
- water molecules are cohesive (stick together) so when some are pulled into the lead, others follow. So the whole column of water in the xylem moves upwards, from leaves down to roots.
- water enters the stem through roots.
What are the four main factors affecting transpiration rate?
- light
- temperature
- humidity
- wind
Outline how light can affect transpiration rate.
The lighter it is, the faster transpiration rate (+ve correlation).
This is because the stomata open when it’s light to let in CO2 for photosynthesis. But when it’s dark, stomata are usually closed so there’s little transpiration.
Outline how temperature can affect transpiration rate.
The higher the temp, the faster transpiration.
This is because warmer water molecules have more kinetic energy so evaporate from the cells inside the leaf faster. This increases the conc gradient between the inside and outside of the leaf, making water diffuse out of the leaf faster.
Outline how humidity can affect transpiration rate.
The lower the humidity, the faster the transpiration rate. (-ve correlation).
This is because if the air around the plant is dry, the conc gradient between the leaf and air is increased, which increases transpiration.
Outline how wind can affect transpiration.
The windier it is, the faster the transpiration rate.
This is because lots of air movement blows away water molecules from around the stomata. This increases the conc gradient, which increased rate of transpiration.
What is a potometer?
Apparatus the estimates transpiration rate.
How doe a apotomotwe measure transpiration rate?
It measures water update by a plant - but it’s assumed that water uptake by a plant is directly related to water loss by leaves.
When investigating the xylem using a potometer, why do you cut the shoot underwater?
To prevent air from entering the xylem.
When investigating the xylem using a potometer, why do toy cut the shoot at a slant?
To increase the SA for water uptake.
When investigating the xylem using a potometer, why, once you’ve removed the leaves from the water do you leave time?
To allow time for the shoot to acclimatise.
