Photosynthesis - the process by which plants utilise energy from sunlight to convert carbon dioxide and water for the synthesis of sugar. This sugar can then be converted to other carbohydrates or other food materials like fats and proteins. The general importance of the process was recognised as long ago as 2000 years. The biblical saint, Isaiah, who lived between 700-600 B.C. said "All flesh is grass" recognising that all food chains are finally traced to plants.
Plants are also responsible for the fossil fuels such as petroleum, oil and coal, which represent products of photosynthesis carried out millions of years ago in the carboniferous era. It is through this process that plants continuously purify air during daytime and thus allow animals to breathe. The overall importance of this process is best expressed in the words of Eugene Rabinowitch, one of the great authors and researchers of photosynthesis, who said "Physiologically speaking, all the animals on land and in the sea, including man, are but a small brood of parasites living off the great body of the plant kingdom", and "if plants could express themselves, they would probably have the same low opinion of animals as we have of fleas and tapeworms - organisms that must lazily depend on others for survival ." The photosynthetic products are utilised by humans and other animals to provide energy.
He proceeded to state that "without them no heart could beat, no amoeba could swim, no sensation could speed along a nerve, no thought could flash in the human brain". Clearly, for all these activities we are dependent on plants.