Algae are amazingly diverse in size, shape and colour. They include a variety of aquatic plants ranging from single-celled plants that are invisible to the naked eye to giant kelps that can grow up to 45 metres and weigh as much as a small tree. Algae can be found on soil, beneath polar ice and in snow, but greatest numbers are found in the waters that cover 70 per cent of the earth's surface. It is the chlorophyll and other photosynthetic pigments that give algae their characteristic colours. Most people have seen piles of green or brownish weed stranded along an estuary or ocean shoreline, or noticed lake waters turn a murky 'pea soup' green colour.
Photosynthesis is the conversion of carbon dioxide and water to carbohydrates using light energy.
Oxygen is produced in the process. The most familiar algae to many people are the large green, brown or red seaweeds, but there are several thousand species of algae and most of them are microscopically small.