Topic 2a- Plant cell organisation

Question 1

What are the layers of cells within a leaf (top to bottom)

Answer 1

• Epidermal tissue
• Palisade mesophyll tissue
• Spongy mesophyll tissue
• Xylem and phloem [somewhere in the middle]
• Epidermal tissue

Question 2

What happens in the palisade mesophyll tissue?

Answer 2

Most of photosynthesis occurs in the palisade mesophyll.

Question 3

What is the main function of the spongy mesophyll tissue?

Answer 3

Containing big air spaces to allow gases to diffuse in and out of cells.

Question 4

What are the functions of meristem tissue?

Answer 4

Found at growing tips of roots and shoots and is able to differentiate into lots of different types of plant cell.

Question 5

What is the function of a waxy cuticle and where is it?

Answer 5

On the epidermal tissues, it helps reduce water loss by transpiration.

Question 6

How is the upper epidermis adapted for its function?

Answer 6

It is transparent so that light can pass through it to the palisade layer.

Question 7

How is the palisade layer adapted for its function?

Answer 7

Lots of chloroplasts for photosynthesis.

Question 8

Describe the structure of a phloem tube.

Answer 8

• made from columns of elongated living cells
• small pores in the end walls to allow cell sap to flow through
• transports food substances (mainly dissolved sugars) mad in the leaves to the rest of the plant
• the transport goes in both directions (translocation)

Question 9

Describe the structure of a xylem tube.

Answer 9

• made of dead cells joined end to end
• no end walls between them
• hole down the middle
• strengthened by a material called lignin
• carry water and mineral ions up the plant from the roots to the stem and leaves (transpiration stream)

Question 10

Explain the transpiration stream.

Answer 10

1. water in the leaf evapourates and diffuses out the leaf through stomata
2. This creates a slight shortage of water in the leaf so more water is drawn up though the xylem vessels.
3. This in turn means that more water is drawn up through the roots.

Question 11

What factors affect the rate of transpiration?

Answer 11

• Humidity
• Air flow
• Light intensity
• Temperature

Question 12

What happens to the guard cells when the plant has lots of water?

Answer 12

The guard cells fill with the water and become plump and turgid. This causes the stomata to open so gases can be exchanged for photosynthesis.

Question 13

What happens to the guard cells when the plant has less water?

Answer 13

The guard cells loose water and become flaccid making the stomata close. This helps stop too much vapour from escaping.