gas exchange (plants) Flashcards
(21 cards)
- What is the role of diffusion in gas exchange?
Diffusion is the process by which gases exchange occurs
- What can single-celled organisms do?
They can exchange gases sufficiently by simple diffusion through the cell membrane
- What do multicellular organisms have?
They have exchange surfaces and organ systems that maximise the exchange of substances
- What do all living cells do?
Respire
- Describe gas exchange during respiration in plants
The process requires the uptake of oxygen and the release of carbon dioxide
Oxygen diffuses down the concentration gradient from a region of high concentration (outside the leaf) to a region of low concentration (inside the leaf) – the cells use oxygen in respiration so the concentration is always low inside the respiring cells
The carbon dioxide diffuses down a concentration gradient from a high concentration (inside the leaf) to a low concentration (outside the leaf)
- What is the structure of the leaf adapted for?
Photosynthesis and gas exchange
- What are arranged in a specific way to facilitate gas exchange and photosynthesis?
The different cell types (palisade mesophyll and spongy mesophyll)
- List the three key gases in gas exchange in a leaf and their functions
Oxygen – released in photosynthesis but used in respiration
Carbon dioxide – released in respiration but used in photosynthesis
Water vapour – released in respiration and transpiration
- What will gases always diffuse down?
A concentration gradient
- Describe the pathway of carbon dioxide from the atmosphere to chloroplast by diffusion
High concentration of CO2 in the atmosphere compared to inside the leaf
This causes CO2 to diffuse into the leaf through open stoma into air space in the spongy mesophyll
CO2 diffuses through the cell wall + cell membrane of spongy mesophyll cell, it dissolves in the cytoplasm and diffuses into chloroplasts
- How is the structure of the whole leaf adapted for gas exchange?
Thin – gives gases a short diffusion distance
Flat – provides a large surface area to volume ratio
Many stomata – allow the movement of gases in and out of the air spaces by diffusion
- How is the internal structure of the leaf adapted for gas exchange?
Air spaces – allow the gas movement around the loosely packed mesophyll cells
Many stomata – in the lower epidermis open in sunlight to allow gas movement in and out of the leaf
Thin cell walls – allow gases to move into the cells easily
Moist air – gases can dissolve into the moist air for easier movement into and out of cells
Close contact – between the cells and the air spaces allows efficient gas exchange for photosynthesis and respiration
- When and how do stomata open and close?
Stomata close when the guard cells lose water by osmosis to the neighbouring epidermal cells and they become flaccid
This prevents any diffusion into or out of the leaf
Stomata tend to close due to low water availability or low sunlight
Stomata open when water moves by osmosis into the guard cells causing them to become turgid
This allows gases to diffuse in and out of the leaf through the stomatal pore
Stomata tend to be open when there is plenty of water and sunlight
- When can plants photosynthesise?
When they have access to light and when they are at suitable temperatures
- During the daytime (at high light intensities) what is the net movement of gas?
Plants respire and photosynthesise
Rate of photosynthesis tends to be higher than the rate of respiration (unless there is a low light intensity)
Rate of photosynthesis reaches a plateau (another factor is limiting)
Therefore, there is a net diffusion of carbon dioxide into the plant and a net diffusion of oxygen out of the plant during the day
This is the light saturation point
- During the nighttime what is the net movement of gas?
At night plants only respire
This means that there is a net movement of oxygen into the plant and a net diffusion of carbon dioxide out of the plant
- At very low light intensities what is the net movement of gas?
The rate of respiration is greater than the rate of photosynthesis
This leads to a net diffusion of oxygen into the plant and a net diffusion of carbon dioxide out of the plant
- At low light intensities what is the net movement of gas?
The rate of photosynthesis is equal to the rate of respiration
This means that there is no net movement of oxygen or carbon dioxide in either direction
This is the light compensation point
- At very high light intensities what is the net movement of gas?
Damage to chloroplasts (chlorophyll gets bleached)
This could result in plant death
What does the net gas exchange of CO2 and O2 depend on?
The intensity of light the plant receives
- Results of the practical: investigate the effect of light on net gas exchange from a leaf, using hydrogen carbonate indicator
After 30 minutes:
a) Control tube –
Remains orange/red colour to show that the carbon dioxide is at atmospheric levels
There has been no net movement of gas
b) The tube placed in the light with a leaf in it –
Leaf is photosynthesising and respiring
The rate of photosynthesis is greater than the rate of respiration, so the hydrogen carbonate indicator will turn purple as there is less carbon dioxide than atmospheric levels
c) The tube that had a leaf inside it but was wrapped in aluminium foil –
No sunlight could reach the leaf meaning that the leaf could not photosynthesise, but will still respire and produce carbon dioxide
The indicator will turn yellow as carbon dioxide levels increase above atmospheric levels
d) The tube wrapped in a gauze with a leaf inside –
The gauze allows partial light through it
This means that the rate of photosynthesis equals the rate of photosynthesis so there is no net change in carbon dioxide levels and the indicator remains orange/red
