In laboratory 5 the process of respiration was examined. All autotrophic and heterotrophic organisms carry on cellular respiration as the method of converting the energy in complex organic compounds such as glucose, to a form usable by the organism. In addition to respiration these organisms also require organic compounds in the synthesis of new protoplasm. The functioning of ecosystems is based on the fixation of energy and the production of organic compounds through the process of photosynthesis by autotrophs.
Photosynthesis is carried out primarily by green plants and algae, both aquatic and terrestrial.
It also occurs in certain pigmented bacteria and in the cyanobacteria. The ultimate energy source for this synthesis of organic compounds is sunlight. The raw materials for photosynthesis are carbon dioxide and water. These two compounds supply the carbon, oxygen and hydrogen that are the predominant elements in organic molecules. It is unfortunate that the above equation tends to give the erroneous impression that photosynthesis is a single step process with carbohydrate synthesis as its major feature.