Chloroplast is an organelle in a plant that carries out photosynthesis. Chloroplasts are large and a mature leaf may contain 20-100. They are described as flattened spheres. New plant cells contain smaller organelles that contain proplastids that can develop into different forms of plastids. For example, amyloplasts are used to store starch, while chromoplasts create pigments for fruits and flowers. Chloroplasts contain chlorphyll which contain the green pigment observed in plants. The membranes within the chlorplast are importnat in the function of photosynthesis. Chloroplasts have an outer and inner membrane that are separated by an intermembrane space. The inner membrane contains ...view middle of the document...
Each pigment has its own absorption spectra that describes the wavelength absorbed. A photoexcited electron either returns to its ground state or transfers to a stable high-energy orbital when in a pigment molecule. If it returns to the ground state, the electron is released as heat or light. If the energy is transferred to an adjacent molecule it is referred to as a resonance energy transfer. If it rises to an excited state and transfers to another molecule, it is referred to as a photochemical reduction. Photochemical reduction is responsible for light energy transforming into chemical energy. Chlorophyll is in almost all photosynthetic organisms. Chlorophyll a and b containa porphyrin ring that absorbs visible light. Chlorophyll a has a broad absorption of about 420 and 660nm and chlorophyll b has a formyl group instead of a methyl group which absorbs the middle of the visible light spectra.
Two Types of Light Reactions (Calvin Cycle and Light-Independent Reactions):
Photosynthesis can be described in two components, the Calvin Cycle and the Light Reaction. The Calvin Cycle is where the reduction of CO2 to O2 takes place. However, it requires energy from the ATP and H produced from the Light Reactions. Both of these functions occur in the chloroplast.
The Calvin Cycle occurs, specifically, in the stroma. Although the Calvin Cycle doesn't require direct light, it does depend on ATP and NADPH, which is provided by the Light Reaction and requires light to be produced itself. There are three steps in the Calvin Cycle:
1. The carboxylation of ribulose-1,5-bisphosphate, and generation of two 3-phosphoglycerate molecules.
2. Reduction of 3-phosphoglycerate into glyceraldehyde-3-phosphate.
3. Regeneration of the original acceptor to allow continued carbon assimilation.
The Light Reaction occurs in the thylakoid membranes. All of the chlorophyll is contained within the thylakoid membrane and broken into groups called photosystems. Within the photosystems there are, photosystem 1 and photosystem 2. Each type of photosystem has a combination of chlorophyll a and b. All...