Transpiration 9.3 Flashcards

You may prefer our related Brainscape-certified flashcards:
1
Q

Why do we need transpiration?

A

Photosynthesis is the process by which plants make their own food and for that they need both water and Co2. Water has to be transported from the roots to the leaves and Co2 must be taken in through the stomata.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

The exchanges that take place during transpiration

A

The Co2 needed will diffuse down a concentration gradient through the stomata into the air spaces in the leaves and oxygen will diffuse out as it is made as a waste product. Water can also evaporate from the surface of the leaves

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is transpiration

A

It’s the loss of water as a consequence of gas exchange in the leaf. As the stomata open, Co2 diffuses in, down a concentration gradient as the air outside the leaf has higher conc than inside the leaf. Oxygen will diffuse out by the same principle, and while this is happening, water vapour in the air inside the leaf will diffuse out. This loss of water is called transpiration

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are stomata?

A

These are pores in the underside of the leaf that are controlled by guard cells and they can open and close to allow gas exchange to occur.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

When do the stomata operate?

A

The function most in the day as this is when photosynthesis occurs and a lot of gas exchange occurs. They open less at night as no photosynthesis is happening, however because of this they need to take in oxygen for respiration, so some still open.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What happens to water after it’s in the xylem?

A

After it’s been taken up by the root and taken to the xylem, the water will move up the xylem until it reaches the leaves. Here it will move into the cytoplasm of the mesophyll cells in the symplast pathway by osmosis, or will use the apoplast pathway and diffuse across. In the apoplast pathway, the water will evaporate from the freely permeable cellulose walls into the air spaces between the cells inside the leaf. It now exists as water vapour and will move from the internal air, through the stomata to the external air by diffusion.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Transpiration Stream

A

The movement of water from the roots to out of the leaf is called the transpiration stream.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Cohesion tension theory

A

The transpiration stream can move water from the roots to the highest leaves as high as 100m. As the water molecules in the mesophyll cells evaporate, they reduce the water potential in the mesophyll cells, so water from a neighbouring cell will move into it by osmosis along the apoplast and symplast pathway and so on through each cell until it reaches the xylem. Water in the xylem will move into the closest mesophyll cell by osmosis which will decrease the water potential in the xylem. Water molecules will form hydrogen bonds with the lignified cell walls of the xylem which is adhesion and it will also form hydrogen bonds with itself which is adhesion. This will cause capillary action to occur where the water will move up the xylem against gravity. This means water will be drawn up into the xylem continuously and is called the transpiration pull.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Evidence for the cohesion tension theory

A
  • the diameter of trees decreases when transpiration is at its highest in the middle of the day and this is because of the increased pressure in the xylem. When the transpiration rate is at its lowest at night, the diameter of trees will increase
  • when the xylem vessel is broken air will be pulled in instead of water leaking out so no water will be in the stems
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Measuring transpiration

A

You can do this by using a potometer and doing the amount of water taken up in a certain amount of time ands measuring how certain factors affect it. You can measure the amount of water taken up by looking at how much an air bubble moves in a certain amount of time

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Stomata/ Guard Cell Structure

A

They have a thin outer wall and a thick inner wall and less flexible which helps it open by becoming bean shaped. They also have cellulose hoops which prevent it from swelling outwards, instead they elongate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Stomatal Opening

A

When the conditions for photosynthesis are good, the guard cells will actively pump out H+ ions and leave them negatively charged. This charge will cause potassium ion channels to open and potassium ion will flow into the guard cells. This will lower the water potential. Water will then move into the guard cells by osmosis and will increase the turgor pressure of the cell. The thick inner wall isn’t as flexible so wont bend as much as the other wall, this causes the guard cells to become a bean shape and will open and make a stomatal pore.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Stomatal Closing

A

When the gas exchange has occurred, or the conditions are no longer favorable, the potassium ions will move out of the guard cells by facilitated diffusion, which increases water potential inside the guard cells. The turgor pressure is now low and so the guard cells are no longer expanded and will close the stomatal pore.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Factors Affecting Transpiration

A

Light, Temperature, Air Movement, Humidity, Soil Water Availability

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Light

A

Light is will increase the rate of photosynthesis which means you will need more gas exchange and more water uptake. More stomata will be open so more water will be lost by evaporation and diffusion out of the leaf so the rate of transpiration will increase, the more light there is.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Humidity

A

The humidity is the concentration of water vapour in the air. If there’s more water vapour on the outside of the leaf, it will decrease the amount of water vapour diffusing out of the leaf from the inside air, this is because of the lowered concentration gradient. Therefore, the more humidity, the slower the rate of transpiration

17
Q

Temperature

A

Increased temperature will increase the kinetic energy of the water particles so they will evaporate out of the mesophyll cells faster and diffuse out of the leaf faster. The temperature will also increase the concentration gradient between the air outside and inside the leaf, and will make the water evaporate faster as it’s trying to cool the plant down. This will increase the rate of transpiration

18
Q

Air Movement

A

The increased movement of air will increase the rate of transpiration because it’s increasing ventilation. It also means that the air that diffuses out of the leaf won’t be still and surround it, it will be moved away from the leaf so that it doesn’t increase the water potential in the exterior air which would decrease the diffusion of water out the leaf, instead the water vapour will be moved away and the concentration gradient will be maintained.

19
Q

Soil Water Availability

A

If it is very dry, there will be a decreased uptake of water, so the plant will into water stress and the rate of transpiration will be decreased.