About Photosynthesis

      Photosynthesis is carried out by a number of different organisms, which contain the light-absorbing green-colored pigment chlorophyll. There are several types of chlorophyll found, such as chlorophyll α and chlorophyll β. They are both composed of a porphyrin ring (the light-absorbing portion containing a magnesium atom surrounded by a hydrocarbon ring with alternating single and double bonds. The electrons in the alternating single-double bonds absorb light energy and begin the photosynthetic process) and a long hydrocarbon tail (can anchor the chlorophyll molecule in a membrane by associating with the hydrophobic regions of the phospholipid bilayer. Chlorophyll α and chlorophyll β only differ at the positions of –R. Chlorophyll α contains a methyl group and chlorophyll β contains an aldehyde group, the different functional groups may affects the light energy that the molecules can absorb. Chlorophyll α is the primary light-absorbing pigment, transfers the energy of light to the carbon fixation reactions. Chlorophyll β acts as an accessory pigment, absorbing photons that chlorophyll α absorbs poorly.

Cyanobacteria:

      Cyanobacteria were the first organisms to use sunlight to produce oxygen and organic compounds using water and carbon dioxide. In the endosymbiotic theory, an ancestor of cyanobacteria was engulfed by an ancestor of today’s eukaryotic cells. But unlike plant chloroplasts, they contain chlorophyll d.

Stomata:

      Leaf is the photosynthetic organ of plants, and the stomata on the leaves are regulated by the plants to limit water loss and maximize CO2 intake. The size of stomata is controlled by to guard cells. The water follows the diffusion of potassium ions K+, and K+ also associate with the active transport of H+ ions. During the day, sunlight (light energy) activates specific receptors in guard cell membrane, stimulating proton pumps that drive H+ out of cells. This causes K+ move into the cells, and water to follow by osmosis. CO2 that accumulated in the last night also used up and causes osmosis into the cells. The guard cells swell and the stomata open. When there is no enough water, the guard cells are flaccid and the stomata will be closed.

Chloroplast:

      Chloroplast is where the photosynthesis happens. Chloroplasts have two membranes: outer membrane and inner membrane. Within the chloroplast, the semiliquid material is called stroma, and a system of membrane-bound sacs called thylakoids.

 

Light:

      Electromagnetic (EM) radiation: a form of energy that travels at 3X10^8m/s in the form of wave packets called photons. Photons with short wavelength have high energy and those with long wavelengths have low energy.

      Spectroscope: an instrument that separates different wavelengths into an electromagnetic spectrum.

      Photosystems: clusters of photosynthetic pigments embedded in the thylakoid membranes of chloroplasts that absorb light energy and, through light reaction, transfer the energy from photons to ADP, Pi, and NADP+, forming NADPH and ATP.

      Action spectrum: a graph illustrating the effectiveness with which different wavelengths of light promote photosynthesis.

      Absorption spectrum: a graph illustrating the wavelengths of light absorbed by a pigment.

As you can see, the green light is less likely to be absorbed, therefore it it reflected and the leaves show a green color.