Gas exchange in flowering plants Flashcards
How do plants exchange gases
By diffusion
What are the main gases that move in and out of plants?
CO2 and O2 (photosynthesis and respiration)
How does diffusion take place during photosynthesis?
- When a plant is photosynthesising it uses up lots of CO2 inside the plant making more CO2 move into the leaf by diffusion.
- Lots of O2 is being made as a waste product of photosynthesis. Some is used in respiration ans rest diffuses out through the stomata
What does the net exchange of gases depend on?
Light intensity
When does photosynthesis take place?
During the day when there is light available
When do plants respire?
They need to all the time - night and day - to get the energy they need to live
What happens during the day when light intensity is high?
- Oxygen is released and carbon dioxide is taken in
Plants make more oxygen by photosynthesis than they use in respiration and use up more carbon dioxide than they produce
What happens during the night when there is no light?
- Oxygen is taken in and carbon dioxide is released
Plants only respire as there is not enough light for photosynthesis to take place
What are adapted for efficient gas exchange?
Leaves
Give some adaptions of leaves?
- Broad - large sa for diffusion
- Thin - gases travel short distance only
- Air sacs inside leaf - increase sa, gases move easily between cells
- Lower epidermis have stomata - they let gases diffuse out and allow water to escape via transpiration
Why do the stomata close when its dark?
Photosynthesis cannot happen in the dark so they do not need to let in CO2. Also water cannot escape when the stomata are closed to this stops the plant drying out
When else do the stomata close other than when its dark?
When supplies of water from the roots start to dry up - this stops the plant from photosynthesising and drying up and dying
What is the opening and closing of the stomata controlled by?
The guard cells that surround them
What does hydrogen-carbonate indicator show?
Changes in CO2 concentration
What colour is the hydrogen-carbonate indicator in air with normal CO2 concentration?
Orange
What happens to the hydrogen-carbonate indicator when CO2 concentration of air increases?
It changes colour to yellow - more CO2 will dissolve
What happens to the hydrogen-carbonate indicator when CO2 concentration of air decreases?
It changes colour to purple - CO2 will come out of solution
Describe an experiment to show how light effects gas exchange
- Add the same volume of hydrogen-carbonate indicator to four boiling tubes
- Put similar sized healthy leaves into three of the tubes and seal with a rubber bung
- Leave the forth tube empty (control tube)
- Wrap one tube in aluminium foil and the other in a gauze
- Place all tubes in bright light and leave for an hour
What would you expect in the control tube?
No change in the colour of hydrogen-carbonate indicator (stays orange)
What would you expect in the tube with aluminium wrapped around it?
Hydrogen-carbonate indicator should change to yellow - respiration is still taking place but no photosynthesis so the CO2 concentration increases
What would you expect in the tube with gauze wrapped around it?
The hydrogen-carbonate indicator would stay a similar colour (so orange) - with a little photosynthesis and some respiration taking place as equal amounts of CO2 are being taken up and produced by the leaf
What would you expect in the tube with nothing covering it?
The hydrogen-carbonate indicator should change to purple - there will be some respiration but lots of photosynthesis leading to a net uptake of CO2 by the leaf meaning a lower CO2 concentration in the tube
