2.7.2 Leaf Structure

Question 1

The structure of the leaf is adapted to carry out, what?

Answer 1

both photosynthesis and gas exchange

Question 2

The different cell types (palisade mesophyll, spongy mesophyll etc.) and tissues are arranged in a specific way to, do what?

Answer 2

facilitate these processes

Question 3

The leaf is specifically adapted to maximize, what?

Answer 3

gas exchange

Question 4

There are 3 key gases which we must consider, what are they?

Answer 4

Carbon dioxide – released in respiration but used in photosynthesis

Oxygen – released in photosynthesis but used in respiration

Water vapour – released in respiration and transpiration

Question 5

Water vapour – released in respiration and transpiration, what?

Answer 5

a concentration gradient

Question 6

Describe the route of diffusion of carbon dioxide into the leaf

Answer 6

1. Higher concentration of Co2, in atmosphere compared to inside of leaf
2. Co2 diffuses into leaf through open stoma into air space in spongy mesophyll
3. Co2 diffuses through cell wall + cell membrane of mesophyll cell, dissolves in cytoplasm + diffuses into chloroplast

Question 7

Name some of the adaptations of leaves to maximise gas exchange

Answer 7

They are thin which gives a short diffusion distance

They are flat which provides a large surface area to volume ratio

They have many stomata which allow movement of gases in and out of the air spaces inside the leaf to maintain a steep concentration gradient

Question 8

Other adaptations of the internal leaf structure/tissues include, what?

Answer 8

Air spaces to allow gas movement around the loosely packed mesophyll cells

Many stomata in the lower epidermis open in sunlight to allow gas movement in and out of the leaf

Thin cell walls allow gases to move into the cells easily

Moist air which gases can dissolve into for easier movement into and out of cells

The close contact between the cells and the air spaces allows efficient gas exchange for photosynthesis and respiration

Question 9

What is the stomata

Answer 9

Stomata are spaces found between two guard cells predominantly on the lower epidermis of the leaf

Question 10

What are guard cells for

Answer 10

The guard cells are responsible for the opening and closing of the stomatal pore which controls gas exchange and water loss

Question 11

When do the stomata open

Answer 11

Stomata open when water moves (by osmosis) into the guard cells causing them to become turgid

• This allows gases to diffuse in and out of the leaf through the stomatal pore
• Stomata tend to open when there is plenty of water and sunlight

Question 12

What is the definition of turgid

Answer 12

Plant cells which have higher turgor pressure due to the intake of water by osmosis making the cell rigid

Question 13

When do stomata close

Answer 13

Stomata close when the guard cells lose water (by osmosis) to the neighbouring epidermal cells and they become flaccid

• This prevents any diffusion into or out of the leaf
• Stomata tend to close due to low water availability or low sunlight