Light energy is converted into chemical energy and this is stored in bonds of sugar through the process known as photosynthesis. This process is exclusive to plants, and some algae, and is a basic element of plant metabolism. In order for plants to make sugar, they only need light energy, water, and carbon dioxide. The photosynthesis process occurs within the chloroplast, specifically the chlorophyll, which is the green pigment involved in this process.
This process occurs primarily in the leaves of the plant and rarely occurs in the stems or other parts of the plant. A typical plant leaf typically consists of a lower and upper epidermis, the vascular bundle (veins), the mesophyll, and the stomates. There are no chloroplasts in the lower and upper epidermal cells, so plant photosynthesis does not happen here. These plant leaf components serve as protection for the other parts of the leaf. The stomates are responsible for exchanging air and they allow carbon dioxide to go out and allow oxygen to come in. This component of plant leaves are holes primarily found in the lower epidermis. The vascular bundle are an essential player in a leaf's transportation system. They move nutrients and water through the plant as they are needed. Photosynthesis occurs within the chloroplasts that are located within the mesophyll cells.
A chloroplast is composed of many parts including the inner and outer membranes, thylakoids stacked in grana, stroma, and intermembrane space. The thylakoids' membranes are what the chlorophyll is built into. Chlorophyll appears green in color due to absorbing blue and red light, which leaves our eyes unable to see these colors. The green light is seen because it is not absorbed, so chlorophyll is seen as green. The energy absorbed by the blue light and red light is used, which leads to the process of photosynthesis. The green light that is seen does not contribute to photosynthesis because the plant cannot absorb it.
Photosynthesis is a two-part process. A process that occurs in the thylakoid membrane, known as light reaction, is the process that turns light energy into chemical energy. Light is necessary for this process to take place. Several different pigments are involved in this process and the different pigment colors absorb different colors of light. These are only slightly different from each other, then the energy that is created that is passed to the central chlorophyll molecule for this process.
Adenosine triphosphate (ATP), a chemical that cells use to store energy, stores the energy that is harvested by the light reaction. This chemical is very similar to human DNA's building blocks.
Carbon dioxide is converted into sugar within a chloroplast's stroma. This photosynthesis process needs the light reaction products (NADPH and ATP) to occur, but not light. This is referred to as a dark reaction and this leads to sugar formation by involving the Calvin cycle. Most plants feed carbon dioxide into the Calvin cycle directly.