Usually, only one of these factors will be the limiting factor in a plant at a certain time.
This is the factor which is the furthest from its optimum level at a particular point in time.
If we change the limiting factor the rate of photosynthesis will change but changes to the
other factors will have no effect on the rate.
If the levels of the limiting factor increase so that this factor is no longer the furthest
from its optimum level, the limiting factor will change to the factor which is at that point in
time, the furthest from its optimum level. For example, at night the limiting factor is likely
to be the light intensity as this will be the furthest from its optimum level. During the day,
the limiting factor is likely to switch to the temperature or the carbon dioxide
concentration as the light intensity increases.
In practice, the farmer will need to find the optimum growing conditions for the crop,
given the costs of providing extra lighting, heat and CO2. Paraffin lamps have
traditionally been used in greenhouses. Their use increases the rate of photosynthesis
because as well as the light generated from the lamps, the burning paraffin produces
heat and CO2 too.
Investigating the effect of environmental factors on the rate of photosynthesis
One way to measure the rate of photosynthesis is to measure the rate at which oxygen
is given off by an aquatic plant. There are various ways in which oxygen can be
collected and measured. One method is shown in the diagram below.
Alternatively, you can make calcium alginate balls containing green algae and place
them in hydrogencarbonate indicator solution. As the algae photosynthesise, they take
in carbon dioxide which causes the pH around them to increase. The indicator changes
from orange, through red to magenta.
Whichever technique is used, you should change one factor (your independent variable)
while keeping all others constant (the control variables). The dependent variable will be
the rate at which oxygen is given off (measured by the volume of oxygen collected per
minute in the capillary tube) or
the rate at which carbon dioxide is used (measured by the rate of change of colour of
the hydrogencarbonate indicator solution).
The independent variables you could investigate are:
Light intensity. You can vary this by using a lamp to shine light onto the plant or
algae. The closer the lamp. the higher the light intensity.
Wavelength of light. You can vary this by placing coloured filters between the
light source and the plant. Each filter will allow only light of certain wavelengths to pass
through.
CO2 concentration. You can vary this by adcting sodium hydrogencarbonate to
the water around the aquatic plant. This contains hydrogencarbonate Ions, which are
used as a source of carbon dioxide by aquatic plants.
Temperature. The part of the apparatus containing the plant or algae can be
placed in a water bath at a range of controlled temperatures.
Video: Limiting factors of photosynthesis
https://www.youtube.com/watch?v=go8V2GQq268