How does light affect photosynthesis and how does
Light is firstly needed to provide the energy for the light-dependent reaction in photosynthesis - it can't function otherwise!
Rate of photosynthesis increases proportionally to light intensity - as light intensity increases so does photosynthesis.
Eventually, light intensity will reach a saturation point where no amount of increase will make a difference and something else is now the limiting factor.
How does CO2 affect photosynthesis and how does it
CO2 makes up around 0.04% of the atmosphere and is therefore almost always the limiting factor.
Increasing the concentration to 0.4% gives a much more optimum yield but any higher and the stomata start to close.
Therefore on a warm, sunny, windless day - it's usually carbon dioxide that's the limiting factor.
How does temperature affect photosynthesis and how
Photosynthesis (the light-independant reaction) involves enzymes (e.g. Rubisco, ATP synthase). Therefore, temperatures below 10 degrees will cause the enzymes to become inactive, and temperatures above 45 degrees will denature the enzymes.
Additionally, at higher temperatures, the stomata will start to close to avoid loosing water, this will cause less carbon dioxide to enter and therefore, photosynthesis will slow down.
How growers increase plant growth as a result.
Carbon Dioxide: Carbon dioxide is added to the air (e.g. by burning a small amount of propane in a carbon dioxide generator).
Light: Light gets in through greenhouse windows and lamps provide light at night.
Temperature: Glasshouses trap heat energy from sunlight - warming the air.
Heaters and cooling systems are used to maintain an optimum temperature and and air circulation systems can be used to make sure the temperature is constant throughout the greenhouse.