The first step in photosynthesis is the interaction of light with chlorophyll molecules. The chemical structures of the various chlorophyll molecules are based upon the cyclic tetrapyrrole that is also seen in the heme group of globins and cytochromes. Various modifications of this group, namely ring saturation characteristics and substitutions on the rings provide a series of pigment molecules that, as a group, absorb effectively over the wavelength range of 400 nm - 700 nm, the spectrum of . It is the high degree of conjugation of these molecules that makes them so efficient as absorbers of visible light.
You have already studied the "dark reaction" and I will refer you to Dr. Diwan's notes on the subject. As the overall process of photosynthesis involves a series of electron transfer reactions, we are in the realm of oxidation-reduction chemistry, and it would help to review the basics of these processes because we will be going into this topic in greater depth. There is a direct analogy to electron transfer in the mitochondrion, in which clumps of energy are transferred from one electron carrier to another along a "chain" and H+ ions are translocated out, across the mitochondrial membrane, thus generating an electrochemical gradient. The energy inherent in this gradient is used to synthesize ATP in the process of "oxidative phosphorylation." The same processes occur in photosynthesis and the chloroplast, the site of photosynthesis in plants and blue-green algae (but not in photosynthetic bacteria), is the analog of the mitochondrion in eukaryotes.
Light and Dark reactions in photosynthesis ppt - WizIQ
Reaction (2) is known as the "light reaction" and reaction (3) is known as the "dark reaction" but both can take place in the light. However, (2) is light-dependent, whereas (3) is not.
Light Rxn= -light e -ATP & NADPH Step 2.) Dark Rxns ..
In light-dependent reactions (as explained in ), photosynthesis increases with more light. More chlorophyll molecules are ionised and more ATP and NADPH are generated as more light photons are focussed on a green leaf. Even though light is extremely important in light-dependent reactions, it is important to note that excessive light can damage chlorophyll and photosynthesis can reduce.
Light-dependant reactions do rely too much on temperature, water or carbon dioxide, even though they are all necessary for the process to complete. This means cold or hot, the reactions will occur as long as there is enough light.
Photosynthesis; Photosynthesis Chapter 7 6CO.
Both the LHC and the reaction centers are membrane bound structures but there are no chloroplasts in the purple photosynthetic bacteria. The electron transfer processes occur within the cell membrane and the overall process is a cyclic one (i.e., there is no net oxidation-reduction). Protons are transferred across the membrane, from the cytoplasmic side to the outside, establishing a proton gradient whose dissipation drives ATP synthesis. A similar situation holds for the cyanobacteria and plants, but in these organisms, the process occurs in chloroplasts and the overall reaction is not a cyclic one.