What are the 4 factors that affect the rate of transpiration?
1) Temperature
2) Light
3) Wind
4) Humidity
How does light affect transpiration rate?
The lighter it is the faster the rate of transpiration
- When the stomata opens, CO2 can diffuse into the leaf for photosynthesis,
How does temperature affect transpiration rate?
The higher the temperature, the faster the transpiration rate.
- Warmer water molecules have more energy so can evaporate from the cells into the leaf faster,
which creates a water potential gradient between the inside and outside of the leaf, which makes water diffuse out of the leaf faster.
How does humidity affect transpiration rate?
The lower the humidity the faster the transpiration rate
- if the air around the plant is dry, there is a greater water potential gradient between the leaf and the air, increasing transpiration rate.
How does wind affect transpiration rate?
The windier it is the faster the rate of transpiration.
- This is because lots of air movement blows away water molecules , which increases water potential gradient, transpiration rate increases
What does a potometer measure?
measures the water uptake by a plant
For a potometer practical how many variables should you change at one time?
ONLY one variable
- All other variables should be kept constant
Why is the shoot cut under water and at a slant during potometer practical?
- Cut under water to prevent air from entering the xylem
- cut at a slant to increase the surface area available for water uptake.
Potometer practical:
1) Cut a shoot under wate, cut it at a slant
2) Assemble the potometer in water and insert the shoot under water, so no air can enter.
3) Remove the apparatus from the water BUT keep the end of the capillary tube submerged in water in a BEAKER of water.
4) Check that the apparatus is water tight and air tight
5) Dry the leaves and allow the shoots to acclimatise then shut the tap
6) Remove the end of the capillary tube from the beaker of water until ONE AIR BUBBLE has formed, and then put the end of the capillary tube back in.
7) Record the starting position of the air bubble, start a stop watch and MEASURE THE DISTANCE MOVED by the air bubble per unit time.
^This is an estimation of the rate of transpiration
What are xerophytes?
Plants that are adapted to live in dry climates ( e.g. deserts)
- Their adaptations prevent them from losing too much water by transpiration.
What common feature do both marram grass and cacti have that slow down transpiration rate?
They both have a thick waxy water proof layer on the epidermis
which reduces water loss by evaporation
What are 2 adaptations of cacti?
1) They have spines instead of leaves, which reduces the surface area for water loss.
2) Close their stomata at the hottest times of the day where transpiration rates are highest
What are 3 adaptations of marram grass?
1) Roll their leaves, which traps moist area, reducing the rate of transpiration, also reduces surface area for water loss and protects the stomata from wind.
2) Their stomata are sunk in “pits” protecting them from the wind, which reduces the rate of transpiration.
3) There is a layer of hairs on the epidermis, that traps moist air, slowing down the rate of transpiration.
What are hydrophytes?
Plants that are adapted to live in water
E.g. water lilies
These types of plants require adaptations to combat low oxygen levels.
What are 3 adaptations of hydrophytes?
1) stomata is normally in the upper surface of the leaf to maximise gas exchange
2) Flexible leaves and stems, to prevent damage from water currents.
3) Some plants such as water lilies have air spaces in the tissue allowing them to float, or that space can be used to store oxygen to be used in respiration.
- floating on the water increases the amount of light they receive.
- Air spaces in the roots and stems allow oxygen to move from the floating leaves to parts of the plant that are under water.
