Plants are producer organisms, but they need both oxygen for respiration and carbon dioxide for photosynthesis in order to operate as a living organism.
Most photosynthesis happens in leaves, but it can also take place in cladodes and phyllodes, which are modified and flattened stems and petioles.
All of the photosynthetic parts of plants (leaves, cladodes and phyllodes) contain chloroplasts, small organelles where photosynthesis actually takes place.
Photosynthetic parts need stomates or pores to let gases in and out: the opening of the stomates is controlled by the guard cells on either side of the stomate.
Photosynthesis in plants would not take place without the chlorophyll that is contained in the chloroplasts, which is used to produce energetic electrons.
According to serial endosymbiosis theory, chloroplasts were once independent organisms which then found welcoming shelter inside other primitive organisms.
Plants appear to be green because chlorophyll does not extract the energy from green light, and this wavelength is reflected away from the leaf.
In any conditions, there will always be a limiting factor on productivity in plants, some item which is in short supply and so limits photosynthesis.
Plants use at least two different photosynthetic pathways, known as C3 and C4. C4 plants are more efficient than C3 plants in photosynthesis.
The difference between C3 and C4 plants lies in just a few key enzymes, but it leads to curious effects which may be detected long after the plant has died.
The uptake of the stable isotopes of carbon, carbon-12 and carbon-13, varies between C3 (less carbon-13) and C4 plants, which have more carbon-13.
An examination of the stable carbon isotopes in animal material reveals whether the animals ate C3 or C4 plants, and so may indicate past climate details.