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Chloroplasts are an organelle present in plant cells responsible for photosynthesis, thus powering the cell.
Form...
Chloroplasts are surrounded by a double membrane, and are filled with many smaller membrane "pods" to maximize surface area. Chloroplast are usually green, and thus responsible for the color of plant cells.
Photosynthesis is a process conducted in chloroplasts, converting CO2 and H2O and producing C6H12O6 (Sugars) and O2.
Photosynthesis can be broken down into two stages, the first being the light-dependent stage(LDS), which, as implied by the name can only take place when light is present. The products of the Light Dependent Reaction are ATP, NADPH and H+.
Photosystem 2...
The LDS begins in photosystem 2. (Despite the name, which refers to it being discovered after photosystem 1)
Photosynthetic Pigments, labeled on the diagram above as "Pigment molecules" get excited by photons of sunlight, to the point of losing electrons that are then lost, hopping between pigment molecules, to the "reaction-center complex" which is a specific molecule of Chlorophyl a. The reaction-center complex enters a high-energy state, said to be "photoactivated", and as a result, high energy electrons are released.
Photolysis...
The holes left behind by the lost excited electrons are positively charged and are powerful enough to split water molecules into hydrogen and oxygen. This is called photolysis.
The process of photolysis uses enzymes that are found in Photosystem II, as a result, hydrogen ions, electrons (unexcited) and oxygen atoms are released. Additionally, the holes are refilled with electrons.
H2O 2H++ 2e- + ½O2
The oxygen atoms combine and are released as a waste product.
Proton Pumps...
The high energy electrons released from Photosystem II are passed along a chain of electron carriers. This provides the energy needed to pump hydrogen ions from the stroma into the thylakoid space. Said transfer of excited electrons occurs between carriers in the thylakoid membranes
Photophosphorylation...
The use of light energy to convert ADP to ATP. Conducted by ATP Synthase across the membrane of the thylakoid space.
Photosystem 1...
The high energy electrons lost from PS2, which lost their energy to the proton pumps, arrive at Photosystem I and fill the holes in the reaction center created by the photoactivation of the primary pigment. Photoactivation of Photosystem I also creates ‘excited’ electrons. These combine with the hydrogen ions from photolysis to reduce NADP+
2H+ + 2e- + NADP
Excited electrons from Photosystem I are used to reduce NADP.
Photosynthetic pigments are molecules that absorb photons of light to excite electrons.
Action and Absorption Spectra...
Absorption...
Chlorophyl A and B are a photosynthetic pigments and are always present in chloroplasts. In addition to chlorophyl, chloroplasts have accessory pigments.
Each different photosynthetic pigment absorb different wavelengths of light less or more.
Carotenoids are an example of accessory photosynthetic pigments, which stand to extend the range of wavelengths of light plants can use to photosynthesize as each photosynthetic pigment will be able to absorb a different range of wavelengths.
The graph above is called an absorption graph, and graphs the amount of light absorbed by the molecules for the visible light spectrum.
Action...
Below is an absorption and action spectrum overlayed. The semitransparent graphs are the absorption spectrum of multiple photosynthetic pigments, and the fully colored line (the action spectrum) plots the rate of photosynthesis at different wavelengths of lights.
Plants photosynthesize at all other colors other than green, as they hold multiple pigments that are sensitive to multiple points on the color spectrum, demonstrated by the peaks in the absorption spectra.
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