Summary Stage I: Light-Dependent Reactions.
The light-dependent reactions transform light energy into chemical energy which is trapped and carried by ATP and NADPH to the Calvin Cycle.
The light-dependent reactions require chlorophyll and occur in the thylakoid membranes of the grana of the chloroplast.
Light energy is also used to split water (Photolysis of water) into:
H2O -----> 2H+ + 2e- + 1/2 O2 This reaction produces oxygen and provides electrons and Hydrogen for the reduction of NADP to NADPH (NADP gains H+ and electrons; the water is oxidized because it loses the H+and e-)
The light reactions remove electrons from excited chlorophyll molecules in both Photosystem I and Photosystem II and pass the higher energy electrons along an electron transport chain, releasing energy to make ATP (from ADP and P), or transferring the electrons to NADP.
The light reactions must occur several times to produce enough ATP and NADPH to "run" the Calvin cycle Stage II: Calvin Cycle or C-3 Photosynthesis
(Sometimes called the Dark Reactions)
Six molecules of Carbon dioxide each combine with a 6 molecules of a 5-carbon sugar (Ribulose bisphosphate) and undergo a reduction to form 3-carbon molecules (Glyceraldehyde 3 Phosphate or G3P).
Ten of the 12 molecules of G3P are used to regenerate more ribulose bisphosphate to keep the cycle going.
Two of the 12 G3P are converted to the carbohydrate, glucose.
These photosynthetic reactions do not use light energy for the energy source.
Photosynthesis occurs in the chloroplasts, specifically, in the grana and stroma regions. The grana is the of the organelle; a collection of disc-shaped membranes, stacked into columns like plates. The individual discs are called thylakoids. It is here that the transfer of electrons takes place. The empty spaces between columns of grana constitute the stroma (The Cell: A Molecular Approach 2nd Ed, Sinauer Associates, 2000).
Changes in redox potential during photosynthesis - …
Anoxygenic photosynthetic and oxygenic photosynthetic organisms use different electron donors for photosynthesis. Moreover, anoxygenic photosynthesis takes place in only one type of reaction center, while oxygenic photosynthesis takes place in two, each of which absorbs a different wavelength of light, according to Govindjee and Whitmarsh. However, the general principles of the two processes are similar. Below are the steps of photosynthesis, focusing on the process as it occurs in plants.
Photosynthesis - Rensselaer Polytechnic Institute (RPI)
(3) Exciton Transfer (Resonance Energy Transfer): Transfer of energy to a nearby unexcited molecule with similar electronic properties. This can happen because the molecular orbital energy levels of the molecules overlap. This mechanism will play an important role in photosynthesis.
Concept 1: An Overview of Photosynthesis - …
Photosynthetic organisms contain organelles called plastids in their cytoplasm. According to Cheong Xin Chan and Debashish Bhattacharya of Rutgers University (), the double-membraned plastids in plants and algae are referred to as primary plastids, while the multiple-membraned variety found in plankton are called secondary plastids. These organelles generally contain pigments or can store nutrients. In “” (Sinauer Associates, 2000), Geoffrey Cooper enumerates the various plastids found in plants. Colorless and non-pigmented leucoplasts store fats and starch, while chromoplasts contain carotenoids and chloroplasts contain chlorophyll.
PHOTOSYNTHESIS - Estrella Mountain Community …
most photosynthesis takes places in leaves, mesophyll cells and organelles known as chloroplast The first step in photosynthesis is the absorption of light energy to be used in the chloroplast.
Photosynthetic efficiency - Wikipedia
I went on to show how the food web diagram can illustrate the potential impact within an ecosystem if a species is eliminated by any means — either natural or by the activities of mankind.