What is Photosynthesis?
Green plants are also called producers. This is because they have the ability to produce their own food from the raw materials around them by a process called photosynthesis.
During photosynthesis radiant energy from the sun (sunlight) is absorbed by green plants. The energy is used to convert carbon dioxide, water and minerals the plants take in from their surroundings into sugar and gaseous oxygen.
Photosynthesis is critical to life on Earth. Without photosynthesis the food supply would finish and the Earth’s atmosphere would lose its oxygen.
Photosynthesis Reaction
The chemical equation for the process of photosynthesis is given as:
| carbon dioxide | + | water |
| 6CO2 | 6H2O |
chlorophyll
| glucose | + | oxygen |
| C6H12O6 | 6O2 |
The photosynthesis equation is a simple representation for a very complex natural process. Within the photosynthesis process there are two distinctly separate stages, a photochemical stage followed by a biochemical stage.
The photochemical stage involves the radiant energy supplied by sunlight and involves reactions called light dependant reactions. Green plants contain a light absorbing pigment called chlorophyll. When a molecule of chlorophyll absorbs light it uses the energy to boost electrons to a higher energy level and the molecule is said to be excited. The electrons at the higher energy levels are transferred along chains of electron carrier molecules. The energy transfers of the electrons are responsible for the formation of key energy carrying molecules along with the splitting of the water molecule to oxygen and hydrogen.
These molecules then undergo the second stage of photosynthesis, the biochemical reaction. Here they react with hydrogen formed from the splitting of water in the photochemical stage and carbon dioxide from the atmosphere with the presence of enzymes to form the organic glucose molecules. The reactions in this stage are referred to as light-independent reactions because they do not require light as they use the energy already provided by the light in the light-dependent reactions. Thus, photosynthesis has transferred the energy from light to chemical energy in the sugar.