Plants create their own energy food, called glucose, through a process called photosynthesis. To carry out photosynthesis plants need four things: chloroplasts, light, water and carbon dioxide. Everything else the plant makes itself. The only things gardeners need to provide for the plant are light and water. The chloroplasts and carbon dioxide are provided elsewhere or are a part of the plant.
The chloroplast is where photosynthesis takes place, and the plant already has it. There are two parts of the chloroplast that are the most important to photosynthesis. The thylakoid is what holds the chlorophyll that is necessary to make the energy source ATP (adenosine triphosphate) and the reducing agent NADPH (nicotinamide adenine dinucleotide). The stroma is where photosynthesis ends and glucose is made.
Light is the most important ingredient in photosynthesis and where the process gets its name. The more light a plant receives, the more glucose it can make to supply energy. Some plants require more light than others to complete the process. The light enters the thylakoid in the chloroplast. The chlorophyll inside reacts to the light and creates electrons. The electrons produce ATP. The use of light is part of the photosynthesis process called the light dependent reaction.
During the light dependent reactions, water molecules are split. Plants get the water from rain or a helpful gardener. When the water molecules are split, this creates electrons, NADPH and oxygen. The electrons replace the ones lost by the chlorophyll, and the oxygen is released. The NADPH and the ATP created from the light continue the process to make glucose.
During the light independent reaction of photosynthesis, also called the Calvin cycle, plants use CO2 (carbon dioxide) from the atmosphere. As soon as the CO2 enters the process, it becomes GP (glycerate 3-phosphate). The energy ATP and the reducing agent NADPH are used to turn the GP into GALP (glyceraldehyde 3-phosphate). Some of the GALP becomes glucose, and the rest continues the Calvin cycle by turning more CO2 into GP.