5.6.9 Factors affecting the rate of photosynthesis Flashcards
What are the several factors needed for photosynthesis to occur?
- Presence of photosynthetic pigments
- Supply of carbon dioxide
- Supply of water
- Light energy
- Suitable temperature
What happens if there is a shortage of the factors needed for photosynthesis
Then photosynthesis cannot occur at its maximum possible rate
What are the main limiting factors of photosynthesis
- Light intensity
- Carbon dioxide concentration
- Temperature
How does light intensity affect the rate of photosynthesis?
The rate of photosynthesis increases as light intensity increases, as more energy is supplied to the plant and therefore the LDR can occur faster.
This produces more ATP and reduced NADP for the Calvin Cycle, which can then occur at a greater rate
What happens if light intensity continues to increase at a certain point?
The relationship between photosynthesis rate and light intensity will be affected and the rate of photosynthesis will reach a plateau.
At this point, light intensity is no longer a limiting factor of photosynthesis - another factor is limiting the rate of photosynthesis (of which coud be temperature - too low/high, or not enough carbon dioxide)
How does carbon dioxide concentration affect the rate of photosynthesis?
The rate of photosynthesis increases as carbon dioxide concentration increases.
It is required for the LIR, during carbon fixation. Therefore the more CO2 that is present, the faster this step of the Calvin cycle, and the faster the overall rate of photosynthesis.
This trend will continue until some other factor required for photosynthesis prevents the rate from increasing furter because it is in short supply
Why is it difficult to increase the level of CO2?
The natural level of CO2 in the atmosphere is 0.04%, it is therefore not advisable to increase the CO2 concentration much higher than this as it can become toxic
How does temperature affect the rate of photosynthesis?
As temperature increases the rate of photosynthesis increases up to an optimum temperature, as the rate of reaction is controlled by enzymes.
However, as the reaction is controlled by enzymes, this trend only continues up to a certain temperature - beyond which the enzymes begin to denature and the rate of reaction decreases.
Temperature does not have a significant affect on the LDR as these are driven by energy from light rather than the kinetic energy of reacting molecules.
However the Calvin cycle is affected by temperature, as the LIR are enzyme controlled
Which stage of photosynthesis is affected the most by temperature
The Light independent reactions, as it involves enzyme controlled reactions.
Whereas the LDR is driven by energy from light rather than kinetic energy of the reacting molecules
What are other effects of temperature on plants other than enzymes
Increasing temperature causes stomata on the leaves to close in order to reduce water loss; when the stomata are closed CO2 cannot enter the leaves and photosynthesis will slow down.
The light dependent reaction relies on a proton gradient forming across the thylakoid membrane; membrane permeability can be influenced by extreme temperatures which may lead to a dissipation of the proton gradient and a slowing down of photosynthesis
How does light intensity affect levels of GP, TP, and RuBP?
A decrease in light intensity causes a decrease in TP and RuBP concentrations but a slight increase in GP concentration.
When there is less light available, the LDR stops and does not form any more products needed for the LIR
As a consequence, GP builds up as it is not converted to TP
A lack of TP means RuBP will not form
Over time carbon fixation will stop and the concentration of GP will plateau
How does very low concentrations of carbon dioxide affect GP, TP, and RuBP levels?
Very low concentrations of CO2 (less than 0.01%) causes a decrease in the concentrations of GP and TP, but an increase in RuBP concentration.
RuBP accepts carbon dioxide so when there is a lack of carbon dioxide molecules it remains unfixed and builds up
The lack of carbon dioxide fixation prevents GP and TP molecules from forming
What can the understanding of the effect of limiting factors on the rate of photosynthesis be used for?
To increase crop yields in protected environments, such as glasshouses.
In the most sophisticated glasshouses, sensors can be used to monitor light intensity, the humidity of the atmosphere, and the CO2 concentration around the crops - allowing the plants to continue growth in the night if they are kept with artificial lighting.
This is also why plants can be grown out of their natural season and habitat because the temperature can be kept constant all year round
How can it be ensured that photosynthesis remains at the highest rate possible
Adjusting/managing the limiting factors by a computer
Water can be supplied by irrigation systems, which may sometime contain added fertilisers or growth nutrients such as nitrates to aid plant growth
Natural pests that may spread disease/eat the crops can be controlled within agricultural settings by pesticides or by seperating the plants from the unfiltered outside air
- This maximises the yield of the crop
Yet farmers have to find a balance between the cost of these maintenances and crop yield as well as the environmental implications this has
How can light intensity be altered in a labatory environment
The distance of the light source from the plant (intensity ∝ 1/d2)
How can temperature be altered in a labatory environment
Changing the temperature of the water bath the test tube sits in
How can carbon dioxide be altered in a labatory environment
The amount of NaHCO3 dissolved in the water the pondweed is in
