Limiting factors in photosynthesis

• Optimum conditions for photosynthesis - vary from one plant species to another
• High light intensity of a certain wavelength: light is needed to provide energy for the LDR - the higher the intensity of the light, the more energy it provides. Only certain wavelengths of light are used for photosynthesis. The photosynthetic pigments chlorophyll a, chlorophyll b and carotene only absorb the red and blue light in sunlight
• Temperature around 25 degrees: photosynthesis involves enzymes (e.g. ATP synthase, rubisco). If the temperature falls below 10 degrees the enzymes become inactive, but if the temperature is more than 45 degrees they may start to denature. Also, at high temperatures the stomata close to avoid losing too much water, this causes photosynthesis to slow down because less carbon dioxide enters the leaf when stomata are closed
• Carbon dioxide at 0.4%: carbon dioxide makes up 0.04% of the gases in the atmosphere. Increasing this to 0.4% gives a higher rate of photosynthesis, but any higher and the stomata start to close
• Water: Plants also need a constant supply of water - too little and photosynthesis has to stop, but too much and the soil becomes water-logged (reducing the uptake of minerals such as magnesium, which is needed to make chlorophyll a)
• Light, temperature and carbon dioxide can all limit photosynthesis. All three must be at the right level to allow a plant to photosynthesise as quickly as possible. If any one of these factors is too low or too high, it will limit photosynthesis (slow it down). Even if the other two factors are at the perfect level, it won't make any difference to the speed of photosynthesis as long as that factor is at the wrong level.
• Agricultural growers (e.g. farmers) know the factors that limit photosynthesis and therefore limit plant growth. This means they try to create an environment where plants get the right amount of everything that they need, which increases growth and so increases yield
• Growers create optimum conditions in a glasshouse
• Carbon dioxide concentration - CO2 is added to the air, e.g. by burning a small amount of propane in a carbon dioxide generator