B2 Transpiration and Stomata (page 41) Flashcards
Transpiration Rate is affted by what Four Main things?
1) Light Intensity
2) Temperature
3) Air Flow
4) Humidity
Why is Transpiration Rate affected by Light Intensity?
The brighter the light, the greater the transpiration rate.
Stomata begin to close as it gets darker. Photosynthesis can’t happen in the dark, so they don’t need to be open to let CO2 in. When the Stomata are closed, very little water can escape.
Why is Transpiration Rate affected by Temperature?
The warmer it is, the faster transpiration happens.
When it’s warm the water particles have more energy to evaporate and diffuse out of the stomata.
Why is Transpiration Rate affected by Air Flow?
The better the air flow around a leaf (e.g. stronger wind), the greater the transpiration rate.
If air flow around a leaf is poor, the water vapour just surrounds the leaf and doesn’t move away. This means there’s a high concentration of water particles outside the leaf as well as inside it, so diffusion doesn’t happen as quickly. If there’s good air flow, the water vapour is swept away, maintaining a low concentration of water in the air outside the leaf. Diffusion then happens quickly from an area of higher concentration to an area of lower concentration.
Why is Transport Rate affected by Humidity?
The drier the air around a leaf, the faster transpiration happens.
This is like what hapens with air flow. If the air is humid there’s a lot of water in it already, so there’s not much of a difference between the inside and the outside of the leaf. Diffusion happens fastest if there’s a really high concentration in one place, and a really low concentration in the other.
How can you estimate the rate of transpiration?
by measuring the uptake of water buy a plant. This is because you can assume that water uptake by the plant is directly related to water loss by the leaves (transpiration).
What is the process of measuring the uptake of water by a plant?
1) Set up the apparatus as in the diagram (pg 41).
2) Record the starting position of the air bubble.
3) Start a stopwatch and record the distance moved by the bubble per unit time, (e.g. per hour).
4) Keep the conditions constant throughout the experiment, e.g. the temperature and air humidity.
What is the piece of apparatus called to measure the uptake of water by a plant? (see diagram on page 41).
it is called a potometer. (see diagram on page 41)
What are Guard Cells adapted to do?
open and close stomata.
What are Guard Cells?
they have a kidney shape which opens and closes the stomata in a leaf. (see page 22, and diagram on page 41).
When the plant has lots of water, explain what the guard cells do?
they fill with it and go plump and turgid. this makes the stomata open so gasses can be exchanged for photosynthesis.
(turgid means swollen/firm typically by fluids)
What happens when the plant is short of water regarding the guard cells?
they lose water and become flaccid, making the stomata close. This helps stop too much water vapour escaping.
(flaccid means soft and hanging loosely or limply, the cells have drawn in and pulled away from the cell wall).
How do the guard cells work regarding their walls?
thin outer walls and thickened inner walls make the opening and closing work.
They’re also sensitive to light and close at night to save water without losing out on photosynthesis.
Where do you usually find more stomata on the leaves?
you usually find more stomata on the undersides of leaves than on the top. The lower surface is shaded and cooler - so less water is lost through the stomata than if they were on the upper surface.
Guard cells are adapted for what?
gas exchange and controlling water loss withing a leaf.
