The Z scheme of photosynthesis, also known as the light-dependent reactions or the electron transport chain, refers to the flow of electrons in the thylakoid membrane of chloroplasts during photosynthesis. It is called the Z scheme because the path of electron flow resembles the shape of the letter "Z" if plotted on a graph.
The Z scheme occurs in the thylakoid membrane, which contains chlorophyll and other pigments that absorb light energy. This energy is used to convert water and carbon dioxide into glucose and oxygen. The process occurs in two photosystems, namely photosystem II (PSII) and photosystem I (PSI).
In PSII, light is absorbed by pigments, primarily chlorophyll a and chlorophyll b. This excites electrons in the pigments, causing them to move to a higher energy level and detach from the chlorophyll molecule. These high-energy electrons are then transferred to an electron acceptor molecule within the thylakoid membrane.
From there, the electrons are passed through a series of electron carriers, including a molecule called plastoquinone. As the electrons move along the carriers, energy is released and used to pump protons (H+) across the thylakoid membrane, creating a proton gradient. This proton gradient is important for the synthesis of ATP, the main energy currency of the cell.
Once the electrons reach PSI, another pigment called P700 absorbs light energy, exciting the electrons. These high-energy electrons are then transferred to a different electron acceptor molecule and continue their journey through a series of carriers, including another molecule called ferredoxin.
Finally, the electrons are transferred to another molecule called NADP+ along with H+ ions, resulting in the production of NADPH, which is used in the dark reactions of photosynthesis to convert CO2 into glucose.
The Z scheme is called so because the energy level of the electron drops after PSI and then rises again after PSII, forming a zigzag pattern resembling the shape of the letter "Z". This flow of electrons allows for the efficient transfer of energy and electrons to produce ATP and NADPH needed for the synthesis of glucose during photosynthesis.
Explain Z scheme of photosynthesis
1 answer