Plant Gas Exchange Flashcards
Autotroph
Something that converts inorganic molecules into organic molecules
Example of an autotroph
Plants as photosynthesis creates glucose an organic molecule from carbon dioxide
What is the equation for photosynthesis?
Water + carbon dioxide -> (light energy + chlorophyll) -> glucose + oxygen (+ATP)
Where does photosynthesis occur
In the chloroplasts
Where are the chloroplasts located
They are packed into the palisade mesophyll mostly and any other areas that are green
Where does the water come from for photosynthesis?
The water comes from the soils, sourced by the roots
Where does the CO2 come from for photosynthesis?
from the air, through the stomata
What happens to the glucose?
1) transported around the plant as sucrose by the phloem and is used by the cells for aerobic respiration
2) stored as glucose energy in starch
3) to make cellulose for cell walls
What happens to the oxygen?
1) Goes out through the stomata, into the air
2) used in aerobic respiration
When does photosynthesis occur
Only daylight hours
When does respiration occur in plants
All the time
Waxy cuticle
Reduce water loss, transparent
Palisade mesophyll layer
Main site of photosynthesis. Cells are deep, elongated and packed full of the chloroplasts which are able to move and arrange themselves in a position within the cell that gives maximum light absorption
Spongy mesophyll layer
Cells contain few chloroplasts and are loosely packed Contains air spaces making it easier for gases to diffuse through the leaf. These cells in the spongy mesophyll are moist on their surfaces aiding in gas exchange surfaces of the spongy mesophyll cells provide a large surface area for gas exchange.
What is the main gas exchange surface on a plant?
The leaf
How do plants have a large surface area?
many air spaces as cells are not tightly packed
How do leaves maintain a concentration gradient? For gas exchange
The palisade cells use carbon dioxide in photosynthesis and the oxygen diffuses down the the diffusion gradient into the air
how are plants moist for gas exchange
There is a thin layer of water molecules that aid in the dissolving in diffusing of gases on the spongy mesophyll.
Upper epidermis
Single layer of cells that’s transparent since no chloroplasts are present. There are not many stomata in the upper epidermis since the heat from direct sunlight would cause excessive evaporation.
What are the gaps between cells called in a leaf?
Intercellular air spaces
Lower epidermis
No waxy cuticle but large number of stomata which open to allow diffusion of gases. Water evaporates from the surfaces of the spongy mesophyll cells and leaves via stoma
How can one identify the xylem compared to phloem?
Xylem is the top one and is darker with larger holes and and there is more inside it
Guard cells
Control the opening and closing of stoma by surrounding the gap that is the stomata. Contains some chloroplasts.
How do plants have a large surface area?
They have a large number of stomata and this maximises the area over which gases can diffuse and therefore the amount of the gases that diffuse
What is the specific significance of a leaf being thin in regards to photosynthesis?
It means the light can penetrate through the leaf
What is the specific significance of a leaf having a large surface area in regards to photosynthesis?
The maximum amount of light energy can be captured
What is the specific significance of a leaf being transparent in the cuticle and upper dermis in regards to photosynthesis?
It means more light can be absorbed allowing a faster at photosynthesis
What is the specific significance of palisade cells being elongated and packed full of moving chloroplasts in regards to photosynthesis?
There is an increased rate of photosynthesis as more light can be absorbed as chloroplasts can move to where there is most light.
Describe a stomata
Found on the underside of the leaf, bordered by two guard cells
Describe guard cells
Borders stomata. Contain chloroplast and found on Lower epidermis. Gases are exchanged between the air and the internal structures of the plant. 90% of water evaporation occur through the stomata
What conditions does the opening of stoma depend on ?
Light intensity and water availability and other atmospheric conditions
When do stoma open ?
Only in the day
What are the guard cells like when the stoma are open vs closed?
They are turgid when open and otherwise plasmolysed
Describe the closing of stoma
Potassium ions in the guard cells diffuse out passively into the epidermal cells, down their concentration gradient. Water moves out of the guard cells by osmosis. The guard cells are now plasmolysed and The stoma closes
Describe the opening of stomata
The chloroplasts in the guard cells photosynthesise, producing ATP. This provides the energy for active transport of potassium ions into the guard cells from the surrounding epidermal cells. Stored starch is converted to malate which is negatively charged. the potassium ions and the mallate are soluble and therefore lower the water potential in the guard cells. As a result water enters the cells by osmosis and the guard cells expand. The thinner cell walls on the outside stretch, whereas the thicker walls on the inside stretch less causing a curved shape to be formed, creating a pore between two of these cells.
Describe the stomata Peel method
Paint 1 cm squared of clear nail varnish on the underside of the leaf. Use a piece of Sellotape to remove the nail varnish with the imprint of stomata. Place the Sellotape on a slide and view under a microscope. Count the number of stoma in the field of view. Repeat three times in different fields of view and calculate a mean
What should you do for reliability in experiments?
Do 3 repeats at least and calculate a mean
What are the two ways to see how reliable your results are?
Using range bars and standard deviation
When can you use range bars? What do large and small range bars Show?
When you have a small sample size of around 3. Large range bars show that there is a lot of variation around the mean. these results are therefore less reliable. This shows the repeats were not reproducible. Small range bars show there is little variation around the mean. These results are therefore more reliable and they show the repeats were reproducible
When can you use standard deviation provide an indication of how reliable your results are?
When you have a large sample size
What does standard deviation tell you?
It gives an indication of the spread of results around the mean. A large standard deviation means the results are less reliable. It allows you to identify anomalies
How does standard deviation allow you to identify anomalies?
Your data should be within 2 standard deviations of the mean (or 95%….?) If it is outside this range it is regarded as anomalous.
What are the limitations of comparing overlapping data?
As soon as you get overlapping data, you can’t significantly say that something has changed.
