Please enable JavaScript.
Coggle requires JavaScript to display documents.
PLANT GAS EXCHANGE - Coggle Diagram
PLANT GAS EXCHANGE
PARTS OF THE LEAVES
Adaptions of the palisade cells:
- Palisade mesophyll are elongated
- Densely packed
- Small air spaces between them
- Contains many chloroplasts
Chloroplasts can move in the cells to collect the most light/ move away from strong light to avoid damage
The cuticle:
- Secreted by the epidermal cells
- Waxy for waterproofing to reduce water loss through the epidermis. The thicker the cuticle, the less water is lost
- It covers both the upper and lower epidermis except at the stomata
- Minimises water loss and prevents gas exchange
- The pores, stomata, allow both water and gases through
Guard cells:
- Change shape to form a stoma for gas exchange
- When water flows into guard cells, the cells become turgid and curve away from each other
- This is because the inner wall is thicker and inelastic compared to the outer wall
- When water flows out of the guard cells the cells become flaccid and the inner walls meet again, closing the stoma
In darkness - no photosynthesis
- Potassium ions diffuse out of the guard cells down a concentration gradient
- Malate is converted to insoluble starch
- Both of the above raise the water potential inside the guard cell
- Water moves out of the guard cell via osmosis down a water potential gradient
- The cells becomes flaccid and the stoma closes
In light - photosynthesis occurs
- Potassium ions move into the guard cells via active transport
- Insoluble starch is converted to malate
- This lowers the water potential inside the guard cell
- Water moves into the cell via osmosis down a water potential gradient
- The cell becomes turgid and the guard cell opens and curves due to the ineer wall of the cell having a thinner inelastic layer of cellulose
- The guard cells have chloroplasts to synthesis ATP which is needed for active transport
Epidermis: - The epidermal cells are transparent - have no chloroplasts
- The guard cells however do have chloroplasts
- Stoma vary in the amount they are opened/closed
- When closed gas exchange is reduced. When opened gas exchange and water loss increases
TYPES OF PLANT
XEROPHYTE
- Plants adapted to dry weather conditions
- They have physical and physiological adaptions to allow them to survive
- A physiological adaption is to close their stomata during the day and open them at night to reduce water loss. One issue with this is that it limits the amount of CO2 supplied to the plant during the day so reduces the rate of photosynthesis
Physical adaptions:
- Leaves are needles or spines - reduces surface area to reduce water loss
- Curled leaves, sunken stomata and hairy leaves - all reduce water loss by creating a damp area and reduces the water potential gradient
- Shallow root that cover a large area
MESOPHYTE
- Plant adapted to normal whether conditions
- It has a few stomata but they are mainly on the lower surface to reduce water loss but there are a few stomata on the top of the leaf
- Waxy cuticle on the top of the leaf to minimise water loss
- Has air spaces that alsows diffusion of gases
HYDROPHYTE
- Plant adapted to very watery conditions
- Only has stomata on the top of the leaf so gases can diffuse in
- Little or no cuticle as it isn't needed because there is free access to water
- Large air spaces for buoyancy
STRUCTURE OF A LEAF
- Waxy cuticle - reduces water loss and clear to allow sunlight to pass through
- Palisade mesophyll - tall to absorb as many photons of light as possible, densely packed in a layer, have many chlorophyll for photosynthesis
- Air Space - to allow gases to circulate
- Bundle sheath cells - contains xylem and the phloem
- Xylem - transpiration
- Phloem - translocation
- Spongy mesophyll - provides large air spaces for gas exchange
- Stoma - open and close to allow molecules to enter and exit the leaves
- Guard cells- cause the opening and closing of the stomata
- Upper epidermis - clear to allow sunlight to pass through
- Lower epidermis
Leaf adaptions:
- Leaves have a large surface area to capture as much light as possible
- Leaves move (slowly) so they are held in a position to gather the most light
- The cuticle and epidermis are transparent so light can get to the mesophyll cells
- Leaves are thin so light can get to lower layers of the leaf
To count the number of stomata on a leaf:
- Take a leaf and add a thin layer of clear nail varnish onto the leaf away from any large vessels
- Once dry get a piece of clear tape and transfer the nail varnish onto the tape
- Stick the tape onto the sample slip
- Count the stomata from 3 different fields of view and calculate a mean
MOVEMENT OF GASES
Daylight:
- Photosynthesis dominant although respiration is still happening
- Carbon dioxide in - carbon dioxide produced by respiration is used in photosynthesis but more carbon dioxide is needed so it has to diffuse in
- Oxygen out - some oxygen is used in respiration but most is diffused out
Darkness:
- Respiration dominant
- Oxygen in
- Carbon dioxide out
- No photosynthesis therefore oxygen diffuses in and carbon dioxide diffuses out
- When its light plants photosynthesise and respirate but only respirate when it is dark
- Gas exchange is needed for respiration and photosynthesis
- Plants rely entirely on diffusion
to enable efficient gas exchange, the leaf is:
- Thin and flat with a large surface area
- It has large air spaces in the spongy mesophyll which allows circulation of gases
- There are smaller air spaces between cells of other tissues
- Stomatal pores are present and can open for gas exchange
- Gases diffuse through stomata down a concentration gradient
- Then gases diffuse through the intracellular spaces between the mesophyll cells
- Gases dissolve in the cellulose cell wall
- Then the gases diffuse into the cell
Standard Deviation
- Calculate the mean
- Value - the mean
- Square the value found from the equation above
- Add all the values from the data together
- Divide the sum of values by the number of values that are given -1
- Square root to get the standard deviation
- Equation will be given if needed