Gas Exchange (Flowering Plants) Flashcards
What is the role of diffusion in gas exchange?
Gases for use in photosynthesis and/or respiration diffuse in or out of the organism, either through specialised exchange surfaces (in multicellular organisms) or the organism itself (in unicellular organisms)
How is gas exchange related to respiration?
- Oxygen is diffused into the leaf from an area of high concentration (outside the leaf) to an area of low concentration (inside the leaf) for use in respiration
- Carbon dioxide diffuses out of the leaf from an area of high concentration (inside the leaf) to an area of low concentration (outside the leaf) as a waste product of respiration
How is gas exchange related to photosynthesis?
- Carbon dioxide is diffused into the leaf from an area of high concentration (outside the leaf) to an area of low concentration (inside the leaf) for use in photosynthesis
- Oxygen diffuses out of the leaf from an area of high concentration (inside the leaf) to an area of low concentration (outside the leaf) as a waste product of photosynthesis
How is the structure of a leaf adapted for gas exchange?
- The leaves are flat and have a high surface area to volume ratio
- Many stomata in the lower epidermis allow diffusion of gases in an out of the leaf to maintain a high concentration gradient
- Air spaces in the spongy mesophyll allow gases for photosynthesis to diffuse faster
- Thin so short diffusion distance for carbon dioxide and oxygen to diffuse in/out
What is the role of stomata in gas exchange?
And how they open and close at different times
- Carbon dioxide and oxygen diffuse in/out of the stomatal pores when they are open
- Guard cells will swell and become turgid through osmosis when there is abundant water and/or sunlight in order to open the stomata for gas exchange
- Guard cells will become flaccid through osmosis when
there is low water and/or sunlight in order to close the stomata to avoid water loss
How does respiration vary with day and night
It does not, respiration is always happening
How does photosynthesis vary with day and night
Photosynthesis is high during the day due to the presence of sunlight, and low during the night because it is dark
How will the net diffusion of gases into a leaf vary with night and day
- The rate of photosynthesis is usually higher than the rate of respiration
- This means that during the day, there is a net diffusion of carbon dioxide into the plant, and oxygen out of the plant
- During the night, there is a net diffusion of oxygen into the plant, and carbon dioxide out of the plant
What colour is hydrogencarbonate indicator at neutral carbon dioxide levels (atmospheric levels)
Orange/red
What colour is hydrogencarbonate indicator at low carbon dioxide levels
Purple
What colour is hydrogencarbonate indicator at high carbon dioxide levels
Yellow
Outline an experiment on the effect of light on net gas exchange of a leaf using hydrogencarbonate indicator
- Set up four test tubes each with 20cm cubed of hydrogencarbonate indicator with a bung on each test tube
- Tube A has no leaf as it is the control
- Tube B has a leaf will full light availability
- Tube C has a leaf and is wrapped in aluminium foil
- Tube D is partially wrapped in aluminium foil
What will be the results of the experiment done in terms of the colour of hydrogencarbonate indicator?
- Control test tube will be orange/red
- Tube with full light availability will be purple as photosynthesis has occurred, using carbon dioxide at a higher rate than respiration produces it
- Tube with no light availability will be yellow, as no photosynthesis has occured but respiration has, leaving high levels of carbon dioxide
- Tube with partial light availability will be orange/red as respiration and photosynthesis have been occuring at the same rate
