B4. Plant transport

Question 1

What is transpiration?

Answer 1

Transpiration is the loss of water vapour (by evaporation) from the surface of the leaf.

Question 2

What is translocation?

Answer 2

The movement of glucose from the leaves (where they are made) to the rest of the plant.

Question 3

What is the function of xylem?

Answer 3

Xylem is a plant tissue which transports water and mineral ions from the roots to the stems and leaves. It is composed of hollow tubes strengthened by lignin.

Question 4

What is the function of phloem?

Answer 4

Phloem is a plant tissue which transports dissolved sugars from the leaves to the rest of the plant. The plant can either use the sugars immediately or store them (as starch).

Question 5

What is the structure of stomata?

Answer 5

They are tiny pores on the surfaces of leaves, which can open or close. Guard cells surround the stomata and control the opening and closing of the stomata.

Question 6

What is the function of stomata?

Answer 6

They allow the exchange of gases in and out of the leaf. Water vapour can also leave through the stomata. They control gas exchange and water loss.

Question 7

Explain how stomata control gas exchange and water loss.

Answer 7

Guard cells open and close the stomata and in this way control the levels of carbon dioxide that enter the leaf and the oxygen & water vapour that leave the leaf by diffusion. i.e. Stomata control gas exchange and water loss.

Question 8

Why is there less water loss through the stomata during conditions of low light intensity?

Answer 8

In low light the guard cells lose water and become flaccid, causing the stomata to close. They would normally only close in the dark when no carbon dioxide is needed for photosynthesis.

Question 9

Where are most of the stomata found?

Answer 9

On the lower surface on the leaf

Question 10

How do mineral ions enter the plant?

Answer 10

Mineral ions are dissolved in water in low concentrations. Therefore the mineral ions (e.g. magnesium, potassium etc) enter the plant via the root hair cells by active transport.

Question 11

Describe how guard cells open and close

Answer 11

• Guard cells have an unevenly thickened (cell) wall

* This enables them to, change shape / bend when they gain water by osmosis.

Question 12

Which conditions cause stomata to OPEN.

Answer 12

• Stomata open during the day and close during the night.
• High water potential outside the stomata
• Light causes stomata to open

Question 13

What is the function of the root hair cells?

Answer 13

To absorb water (by osmosis) and mineral ions e.g. K+ by active transport.

Question 14

How are root hair cells adapted to absorb water and mineral ions?

Answer 14

There are many hairs which gives an increased surface area so the plant can absorb more water by osmosis.

Question 15

How are xylem cells adapted to transport water?

Answer 15

• Composed of dead hollow cells

- They have thick lignified walls which gives strength

Question 16

What is the function of phloem cells?

Answer 16

To transport food (glucose) from the leaves to the rest of the plant for immediate use or storage. This is called translocation.

Question 17

What is the structure of phloem cells?

Answer 17

• Tubes of elongated cells
• Living cells
• Each phloem tube has a companion cell.

Question 18

What is the function of xylem cells?

Answer 18

To transport water from the roots to the leaves.

Question 19

Explain how light intensity affects the RATE of transpiration.

Answer 19

Transpiration rate increases as light intensity increases.

This is because stomata are open wider for gas exchange. More water therefore evaporates.

Question 20

Explain how temperature affects the RATE of transpiration.

Answer 20

At higher temperatures the rate of transpiration increases.

This is because water molecules have more kinetic energy and enzymes can catalyses reactions faster.

Question 21

Explain how humidity affects the RATE of transpiration.

Answer 21

Transpiration rate is faster when conditions are LESS humid.
The less humid the air the less water in it. In this case water molecules will move by osmosis from an area of higher water potential (inside the leaf) to an area of lower water potential (outside the leaf).

Question 22

What are the walls of xylem thickened with?

Answer 22

Lignin

Question 23

Do xylem cells have a nucleus?

Answer 23

No, as they are DEAD hollow cells.

Question 24

Where does photosynthesis take place?

Answer 24

In the leaves of the plant.