[strath76]

Hi Arvin. Plants use CO2 during the day, and expell O2. This is reversed at night. Many years ago in hospitals they would remove flowers from hospital rooms at night as they thought the CO2 may have adverse effects on patients.

In actual affect the amount used and produced, especially in plants the size of CP's, is very small. Here in Australia CO2 is used in the fruit industry to protect crops that have been harvested from pests (mainly larger pests such as mice and rats).

The majority of plants synthesize 'food' in the same manor using the same pathway. These are called C3 plants. Some plants have adapted a slighlty different pathway that has some advantages over teh C3 pathway and these are C4 plants. An example of a C4 plant is Sugar Cane. Whilst the system is different they still rely on the same compounds. If you are really interested in this then check out C3 and C4 plants and also a thing called the Calvin Cycle.