Sun is a major source of energy. All living beings on earth are directly or indirectly dependent on sun. Food chains show that the primary producers are plants and plankton that produce chemical energy, in the form of glucose, from the sun. Fossil fuels that are used to generate electricity are formed from the decayed organic life forms like plants and animals. Sun is hence a major source of energy; plants help earth tap this energy and sustain themselves and other living species. The process of conversion of carbon dioxide and water into glucose in the presence of sun is called as photosynthesis. Glucose readily undergoes a series of chemical reactions to produce energy in plants and animals. While plants make their own food, animals consume it from plants for sustenance. Let’s discuss the physicochemical process by which sun’s radiation energy is tapped in the form of chemical energy. This article is an introduction to photosynthesis, its chemical nature and place of its occurrence in plants.
The leaves of the plants and other green parts are the places where photosynthesis takes place. Photosynthesis is mediated via a chemical called as chlorophyll, a pigment. The cause of green colour of plants is chlorophyll. Chlorophyll is present in tiny parts of plant leaves called as chloroplasts. During the process of conversion of light energy to chemical energy, there is a series of different chemical species that act like a conducting wire moving electrons from one point to the other like what we discussed during our Physics tuition classes on Current of Electricity. This series of chemicals is embedded in chloroplasts. This is the place of generation of a chemical called as NADPH which mediates the generation of glucose from carbon dioxide.
Water and carbon dioxide are two chemicals that are converted into glucose. Plants absorb water from roots and through water potential difference, water reaches the leaves. Leaves directly absorb carbon dioxide present in the atmosphere through tiny pores present on them. These two chemicals act at different places in a plant cell during photosynthesis. One molecule of glucose contains 6 atoms of carbon, 12 atoms of hydrogen and 6 atoms of oxygen. Carbon and oxygen present in glucose are sourced from carbon dioxide. The exact role of light in photosynthesis, how it enables the conversion of small molecules like carbon dioxide and water into a complex chemical form called as glucose as well as why it requires chloroplasts to enable this process, will be discussed in the next article in detail.