Photosynthesis

The photosynthesis process evolved 450 million years ago. With this process, plants convert carbon dioxide and water into carbohydrates using light energy. Carbohydrates synthesized in the photosynthesis process will be distributed to all plant organs to fuel their activities. The photosynthesis process can be described as a chemical equation:

6CO2+6H2O+Light=C6H12O6+6O26CO_{2}+6H_{2}O+Light=C_{6}H_{12}O_{6}+6O_{2}

H2OH_{2}O is absorbed via root, and the gases CO2CO_{2} and O2O_{2} enter and leave the plant through tiny pores in the leaf called stomata.

Photosynthesis occurs within a special cell compartment called the chloroplast. When light is intercepted by leaves, individual photons (particles of light) are absorbed by a pigment called chlorophyll (also responsible for the green color in leaves). Chlorophyll is stashed in membranous sacs called thylakoids. Stacks of thylakoids fuse to form single units called grana. Thylakoids and grana are filled with lumen, and the chloroplast is filled with stroma (see figure below).

Photosynthesis can be divided into light-dependent (Light reaction) and light-independent (Calvin cycle) processes.
Photosynthesis can be divided into light-dependent (Light reaction) and light-independent (Calvin cycle) processes.

Photosynthesis can be divided into light-dependent and light-independent processes. The light-dependent process occurs within the thylakoid membrane and requires a steady photon stream. In this process, photons transfer energy to chlorophyll, and light energy is converted into chemical energy in the form of the molecules ATP and NADPH. The light-independent process (the Calvin Cycle) occurs in the stroma and does not require light. During this process, energy from the ATP and NADPH molecules is used to assemble carbohydrate molecules, like glucose, from carbon dioxide.