upward movement of water

Question 1

What causes pressure in roots?

Answer 1

When water is drawn into roots by osmosis, the build-up of water causes a pressure.

Question 2

What does root pressure do?

Answer 2

Root pressure pushes water up through the xylem.

Question 3

When is root pressure low?

Answer 3

very low in the summer - yet this is when most water passes up through the stem.

Question 4

define transpiration

Answer 4

It is the loss (by evaporation) of water vapour from the leaves and other aerial parts of a plant.

Question 5

Where in a plant does the most transpiration take place?

Answer 5

Most transpiration takes place through openings called stomata (singular, stoma) on the underside of the leaf,

Question 6

Where are stomata located on a plant?

Answer 6

underside of the leaf

Question 7

Water evaporates from the cells in the leaf into what?

Answer 7

Water evaporates from the cells in the leaf into the air spaces.

Question 8

Water evaporates from the cells in the leaf into the air spaces. Where does it diffuse into next?

Answer 8

From the air spaces it diffuses out into the atmosphere through the stomata.

Question 9

When the leaf cells lose water by diffusion into the atmosphere, they become what?

Answer 9

they become less swollen and less turgid and they become more concentrated than the xylem cells.

Question 10

As leaf cells lose water by diffusion into the atmosphere, they become more concentrated than the xylem cells. What does this mean for the water in the xylem?

Answer 10

This means that water passes from the xylem into the cells because of an osmotic gradient.

Question 11

What happens to the water molecules in the xylem during osmosis?

Answer 11

As each water molecule is ‘pulled’ from the xylem cells by osmosis it pulls the next water molecule. This pulling force is transmitted from water molecule to water molecule all the way down the stem and into the root.

Question 12

Why is water said to be pulled up through the plant by transpiration?

Answer 12

As each water molecule is ‘pulled’ from the xylem cells by osmosis it pulls the next water molecule. This pulling force is transmitted from water molecule to water molecule all the way down the stem and into the root.

Question 13

What is the transpiration stream?

Answer 13

The flow of water through a plant is known a the transpiration stream.

Question 14

What is the flow of water through a plant known as?

Answer 14

The flow of water through a plant is known a the transpiration stream.

Question 15

To reduce wilting, what must plants do?

Answer 15

To prevent wilting it is necessary for plants to reduce their rate of transpiration.

Question 16

Explain how the thick cuticle layer reduces the rate of transpiration in a plant.

Answer 16

Leaves have a waxy cuticle through which water cannot pass. The cuticle is normally thicker on the upper surface of the leaf because more water can evaporate from the upper surface of a leaf than from the lower surface.

Question 17

Can water pass through the waxy cuticle of a plant?

Answer 17

no

Question 18

What part of a plant has the thicker layer of a cuticle? why?

Answer 18

The cuticle is normally thicker on the upper surface of the leaf because more water can evaporate from the upper surface of a leaf than from the lower surface.

Question 19

What does the cuticle layer not cover?

Answer 19

The cuticle does not cover the stomata on the lower surface of the leaf.

Question 20

Where are stomata normally located on a plant?

Answer 20

Stomata are normally located on the lower surface of a leaf.

Question 21

What part of a plant is not in direct sunlight and how does this affect the rate of transpiration?

Answer 21

The lower surface is not in direct sunlight and so it is cooler. This helps to reduce water loss by transpiration because the rate of evaporation is higher on the warmer upper surface than on the
lower surface.

Question 22

What is each stoma surrounded by?

Answer 22

Each stoma is surrounded by two guard cells

Question 23

What can guard cells do to stoma?

Answer 23

The guard cells can open or close the stoma by changing shape.

Question 24

When are stomata normally opened? What does this allow to happen?

Answer 24

Normally stomata are open by day.
This allows the leaf to exchange gases for photosynthesis during the day.

Question 25

When are stomata normally closed? What does this help to reduce?

Answer 25

Stomata generally close at night. This helps to reduce water loss from the leaves at night, when gas exchange is not necessary because there is no photosynthesis in the dark.

Question 26

What can cause stomata to close during the day? Why?

Answer 26

However, environmental conditions can cause stomata to close during the day. This happens due to the following conditions:
(a) if the plant loses too much water,
(b) high temperatures and
(c) high wind.
In these cases the rate of transpiration is too great. By closing the stomata the plant reduces water loss.

Question 27

What do stomata do during dry conditions e.g. drought? What effect does this have on food crop yields?

Answer 27

In dry conditions (drought) the stomata will remain closed for much of the time. This is why food crop yields are normally substantially reduced in dry weather.