Gas Exchange In Plants: Leaves

Question 1

Where does gas exchange occur in plants?

Answer 1

In the leaves

Question 2

What is the site of gas exchange in plants?

Answer 2

The palisade cells

Question 3

What are dicotyledonous plants?

Answer 3

A common flowering plants which develops two leaves out of a germinating seed

Question 4

Movement of CO2 through the plant

Answer 4

1) Carbon dioxide enters via stomata which are opened by guard cells
2) It diffuses into air spaces in the spongy mesophyll down a concentration gradient
3) Palisade mesophyll have a lower concentration of carbon dioxide owing to photosynthesis so it moves from air spaces into palisade cells down a concentration gradient gradient

Question 5

Movement of O2 through a plant

Answer 5

1) Oxygen is produced during respiration so moves from palisade mesophyll to the air spaces of the spongy mesophyll down a concentration gradient
2) From the air spaces it diffuses out and leave the plant via stomata which are opened by the guard cells down a concentration gradient

Question 6

Adaptations of the leaf for gas exchange

Answer 6

•Flat -> Large surface area to volume ratio
•Many stomata -> Allow air to move in and out
•Air spaces in spongy mesophyll -> Short diffusion pathway between palisade mesophyll and air spaces

Question 7

Adaptation of the leaf to reduce water loss

Answer 7

•Guard cells close stomata at night -> Less CO2 is required due to lack of sunlight available so less photosynthesis occurs
•Upper and lower waxy cuticles -> Trap water as it’s impermeable
•Most stomata on the lower epidermis -> Less sunlight intensity focussed on the bottom so less evaporation
•Air spaces saturated with water vapour from xylem to reduce water potential gradient

Question 8

What are xerophytes?

Answer 8

Plants that live in dry and arid environments

Question 9

Examples of xerophytes

Answer 9

Cacti and a huge variety of succulents

Question 10

What is transpiration?

Answer 10

Movement of water from root to leaf

Question 11

Adaptations to reduce water loss in xerophytes

Answer 11

•Thick waxy cuticle -> Increased diffusion distance to reduce transpiration
•Hairs around stomata, sunken into pits and rolled leaves -> All trap water vapour and decrease the water potential gradient
•Leaves reduced to spines -> Reduce SA:V ratio which reduces transpiration
•Small leaves with reduced number of stomata -> Less access to leave so reduced transpiration