Unit 3, gas exchange in plants

Question 1

What does the stomata do and what point of the leaf is it at?

Answer 1

It’s at the lowest point of a leaf, gas exchange occurs here

Question 2

What does the spongy mesophyll do and what point of the leaf is it at?

Answer 2

it lies above the stomata, it has lots of space to allow gases in and maintain concentration gradients, co2 diffuses in

Question 3

What does the palisade mesophyll do and what point of the leaf is it at?

Answer 3

It is above the spongy mesophyll, co2 enters in to palisade after being in the spongy, photosynthesis occurs here as it receives the most direct sunlight.

Question 4

Where does gas exchange occur?

Answer 4

At the stomata

Question 5

what gas goes in and what gas goes out

Answer 5

Carbon dioxide in, oxygen out

Question 6

Why do plants constantly need carbon dioxide

Answer 6

Carbon dioxide is required for photosynthesis, so the plant constantly needs it,

Question 7

how does carbon dioxide diffuse in?

Answer 7

The spongy mesophyll has a lower concentration, than the area surrounding there carbon dioxide diffuses in

Question 8

How does oxygen diffuse out?

Answer 8

there is a higher concentration of oxygen in the area surrounding, than in the spongy mesophyll, therefore oxygen can diffuse out

Question 9

when does the stomata close and why?

Answer 9

to reduce water loss by evaporation, stomata closes at night when photosynthesis isn’t taking place

Question 10

what are xerophytic plants adapted for?

Answer 10

They’re adapted to survive in environment with limited water, eg desert

Question 11

What structural features does a xerophytic plant have ?

Answer 11

• hairs to trap moisture, to make it more humid, reducing water potential, so less water loss
• leaf curls up, this traps water that evaporates making it more humid, preventing evaporation
  -stomata is sunken further into the leaf, preventing water loss as more humid
  -longer roots, to gain more water
  -thicker cuticle, to reduce evaporation

Question 12

How does humidity effect water potential?

Answer 12

• if it’s humid around a plant then there is moist air outside of the plant, so there is a less negative water potential, this decreases water potential gradient between inside and outside of the plant.

Question 13

How do potassium ions open and close the stomata?

Answer 13

• they cause there to be a lower water potential, causing water to enter guard cells by osmosis making cells turgid
• causes cells to bend, opening the stomata.