Photosynthesis results in an increase in ; i.e. there is more carbohydrate in the plant. They can turn some of the glucose into fat or protein. They have to make lots of different chemicals to grow, but the two most important ones are fats and proteins. To do this they need energy (growth requires energy from glucose). Plants also have to make a very special chemical called DNA: this is the hereditary chemical of all animals and plants. They must also make lots of new chlorophyll.
Carbon dioxide and water are inorganic chemicals, whereas glucose is an organic chemical. Plants need energy to convert carbon dioxide and water into glucose; this energy comes from sunlight. Plants can also use artificial light providing that it contains the right frequencies (). Light energy is trapped by a green chemical called chlorophyll. In photosynthesis, light energy is converted into chemical energy. When animals and plants respire, the chemical energy in glucose can be converted into other forms of e.g. kinetic energy.
Light absorbed by chlorophyll or other photosynthetic pigments is used to drive a transfer of and hydrogen from water (or some other donor molecule) to an acceptor called +, reducing it to the form of NADPH by adding a pair of electrons and a single proton (hydrogen nucleus).
During dark adaptation, all the reaction centres are fully oxidised and available for photochemistry and any chlorophyll fluorescence yield is quenched. This process takes a variable amount of time and depends upon plant species, light history prior to the dark transition and whether or not the plant is stressed. Typically, 15 – 20 minutes may be required to dark adapt effectively. In order to reduce waiting time before measurement, a number of leaves may be dark adapted simultaneously using several leafclips. Some users even make measurements at night, thus ensuring an adequate supply of readily dark adapted samples and zero waiting time!