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The light excites an electron from the chlorophyll a pair, which passes to the primary electron acceptor. The excited electron must then be replaced. In (a) photosystem II, the electron comes from the splitting of water, which releases oxygen as a waste product. In (b) photosystem I, the electron comes from the chloroplast electron transport chain.
In the Light-Independent Reactions, two compounds, NADPH and ATP, carry the energy from light that was originally transformed into hydrogen ions and electrons through the splitting of water. The NADPH and ATP, along with carbon dioxide from the atmosphere, enter a process called the Calvin Cycle , where the energy is used to fix carbon into a molecule abbreviated G3P as shown in Figure ...
Embedded in the thylakoid membrane are molecules of chlorophyll, a pigment (a molecule that absorbs light) through which the entire process of photosynthesis begins. Figure 4. This equation means that six molecules of carbon dioxide (CO2) combine with six molecules of water (H2O) in the presence of sunlight.
Figure \(\PageIndex{7}\): A photosystem consists of a light-harvesting complex and a reaction center. Pigments in the light-harvesting complex pass light energy to two special chlorophyll a molecules in the reaction center. The light excites an electron from the chlorophyll a pair, which passes to the primary electron acceptor.
- How The Light-Dependent Reactions Work
- Generating An Energy Molecule: ATP
- Generating Another Energy Carrier: NADPH
- Section Summary
- References
The overall purpose of the light-dependent reactions is to convert solar energy into chemical energy in the form of NADPH and ATP. This chemical energy will be used by the Calvin cycle to fuel the assembly of sugar molecules. The light-dependent reactions begin in a grouping of pigment molecules and proteins called a photosystem. There are two phot...
In the light-dependent reactions, energy absorbed by sunlight is stored by two types of energy-carrier molecules: ATP and NADPH. The energy that these molecules carry is stored in a bond that holds a single atom to the molecule. For ATP, it is a phosphate atom, and for NADPH, it is a hydrogen atom. Recall that NADH was a similar molecule that carri...
The remaining function of the light-dependent reaction is to generate the other energy-carrier molecule, NADPH. As the electron from the electron transport chain arrives at photosystem I, it is re-energized with another photon captured by chlorophyll. The energy from this electron drives the formation of NADPH from NADP+ and a hydrogen ion (H+). No...
The pigments of the first part of photosynthesis, the light-dependent reactions, absorb energy from sunlight. A photon strikes the antenna pigments of photosystem II to initiate photosynthesis. The energy travels to the reaction center that contains chlorophyll ato the electron transport chain, which pumps hydrogen ions into the thylakoid interior ...
Unless otherwise noted, images on this page are licensed under CC-BY 4.0 by OpenStax. Text adapted from: OpenStax, Concepts of Biology. OpenStax CNX. May 18, 2016 http://cnx.org/contents/b3c1e1d2-839c-42b0-a314-e119a8aafbdd@9.10
- Lisa Bartee, Walter Shriner, Catherine Creech
- 2017
When the stomata are closed, carbon dioxide cannot enter the leaves to form glucose in the light independent reactions. When the light independent reactions are not occurring, energy stored in ATP and NADPH cannot be transferred to carbon-carbon bonds and so eventually the light-dependent reactions will run out of ADP and NADP to accept electrons.
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How do two photosystems absorb light energy?
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What is a light reaction in photosynthesis?
Nov 13, 2024 · In light reaction I, electrons are passed on to iron-sulfur proteins in the lamellar membrane, after which the electrons flow to ferredoxin, a small water-soluble iron-sulfur protein. When NADP + and a suitable enzyme are present, two ferredoxin molecules, carrying one electron each, transfer two electrons to NADP + , which picks up a proton (i.e., a hydrogen ion) and becomes NADPH.
