The process of photosynthesis as carried out by the chloroplast is arguably the most important biochemical process that occurs on the planet. Whilst many organisms gain their energy and carbon molecules by consuming other organisms in a heterotrophic manner, ultimately the basis of all food chains is the energy and carbon which is accumulated by autotrophic organisms carrying out photosynthesis. All of these organisms either contain photosynthetic chloroplasts or are single-celled organisms, such as photosynthetic bacteria, which carry out photosynthesis themselves. Such photosynthetic organisms are autotrophic in that they obtain their energy directly from the light emitted from the sun, a result of nuclear fusion. The light energy is transduced into energy stored in molecular bonds, which is then used to drive a complex series of biochemical reactions, which enables the fixation of gaseous carbon dioxide (CO2) molecules from the air. This fixation process involves binding of the CO2 to simple phosphorylated sugar molecules located in the stroma of the chloroplast, which eventually give rise to related phosphorylated sugar molecules which are either exported or retained in the chloroplast and give rise to biochemical pathways which synthesise sucrose or starch. In this way, plants can grow and increase in biomass by accumulating carbon molecules from the atmosphere and subsequently they synthesise a myriad of large complex carbon-based molecules. Probably the most abundant of these is the polymer cellulose, composed of long chains of glucose molecules, which forms the basic structure of plant cell walls and comprises a significant proportion of global plant biomass.