3. Plants and Xerophytes

Question 1

How are palisade cells adapted to their function

Answer 1

Long , thin cells that form a continuous layer
Numerous chloroplasts that arrange themselves in the best positions to collect maximum amount of light
A large vacuole that pushes the cytoplasm and chloroplasts to the edge of the cell

Question 2

Adaptations of the leaf

Answer 2

The flattened shape provides a large surface area compared with the volume. Simple diffusion therefore allows gas exchange.
The main surface for this is the mesophyll cells.
The pores called stomata, mostly in the lower epidermis, allow gases to move into and out of the leaf.
Guard cells control opening and closing of stomata.

Question 3

Xerophytes Adaptations

Answer 3

Reduced leaves - less SA
Swollen stems - 
Deep roots
Few stomata
Sunken Stomata - reduces water potential gradient

thick cuticle -greater diffusion distance
Hairs- traps air which becomes saturated

Question 4

Guard cells

Answer 4

Stomatal opening and closing is controlled by the guard cells. The inner wall of the guard cell is thicker than the outer wall. Guard cells also contain chloroplasts.
When the stoma is open the guard cells are TURGID. This is due to water entering them.
When the stoma are closed the guard cells are FLACCID.

Question 5

Leaf Adaptation

Answer 5

The main function of a leaf is to carry out photosynthesis; for this it needs a supply of carbon dioxide and water and sunlight. Sunlight will not penetrate far so the leaves need to be thin and to get enough carbon dioxide they need a large gas exchange surface.

Question 6

Gas exchange in the leaf

Answer 6

Plants need carbon dioxide for photosynthesis. Oxygen is produced and CO2 used in this process.
Respiration uses oxygen and produces CO2 so the rate and type of gases exchanged with the environment depends on the balance between the rate of these reactions.

Question 7

Marram grass has a

Answer 7

Thick cuticle
Rolled leaves
Hairs

Question 8

Cacti

Answer 8

These have
Reduced leaves
Swollen stems
Deep roots
Few stomata

Question 9

Describe and explain how three structural features reduce the rate of transpiration in xerophytic plants.

Answer 9

Rolled leaves - reduces water potential gradient / air movement across stomata/traps air which becomes saturated/ moist/humid/ reduces surface area;

Sunken stomata - reduces water potential gradient / air movement across stomata / traps air which becomes saturated/ moist/humid:

Thick cuticle - Reduces cuticular transpiration / reduces evaporation / greater diffusion distance;

Hairs - traps air which becomes saturated / moist / humid:

Reduced leaves / spines - less surface area / fewer stomata (for evaporation),

Question 10

Describe two features you would expect in the leaves of a xerophyte which would reduce the rate of transpiration.

Answer 10

Thick cuticle; hairs; sunken stomata; inrolled leaves; fewer stomata Reduced leaf surface area;