Gas exchange in plants

Question 1

What is the role of diffusion in gas exchange?

Answer 1

Takes place on underside of leaf in stomata
Stomata open in the light
CO2 diffuses in
O2 diffuses out

Question 2

Describe gas exchange (of carbon dioxide and oxygen) in relation to respiration and photosynthesis

Answer 2

Day - photosynthesis and respiration
Light -> O2 out of chloroplast into mitochondria and out of cell
CO2 out of mitochondria into chloroplast and out of cell
Night - Respiration only
O2 in, CO2 out

Question 3

Describe how the structure of the leaf is adapted for gas exchange

Answer 3

large surface area - allow more CO2 to enter
thin - so gases have short diffusion distance
Stoma allow gases to enter and exit
Air spaces in spongy mesophyll layer - allow gases to diffuse throughout leaf
Stoma - spread out over leaves allowing more CO2 to enter

Question 4

Describe the role of stoma in gas exchange

Answer 4

Plants take in air through stomata on the underside of leaves
They open in the light allowing CO2 in for photosynthesis
At night they close
Stomata also close in hot, dry weather to reduce water loss through transpiration

Question 5

How is respiration affected by time of day?

Answer 5

Respiration continues during the day and night, but the net exchange of carbon dioxide and oxygen depends on the intensity of light

Question 6

What are the origins of carbon dioxide and oxygen?

Answer 6

The origin of carbon dioxide and oxygen are as waste products of metabolism and their lost through the stomata of a leaf

Question 7

Plants respond to…

Answer 7

Stimuli - light and gravity

Question 8

Describe the geotropic responses of roots and stems

Answer 8

Geotropism - response to the pull of gravity
Positively geotropic - roots growing down towards source of water and mineral ions and helps anchor plant
Negatively geotropic - shoots, growing up towards the light

Question 9

Describe the phototropic responses of roots and stems

Answer 9

Phototropism - A growth response to light
Positively phototropic - shoots and leaves grow towards the light (usually up) to maximise light intake
Negatively phototropic - roots grow away from light, so they grow into the ground where the nutrients are and helps anchor the plant

Question 10

What is auxin?

Answer 10

Plants make a hormone called auxin 
Makes cells in the stem grow faster and longer 
Made in the tips of shoots
Diffuses down the stem
Moves away from the light

Question 11

Describe the role of auxin in the phototropic responses of stems

Answer 11

Auxin is a hormone that moves away from the light
If light is coming from one direction, auxin will move to the shaded side
The cells in this part of the stem grow longer causing the stem to bend towards the light