P680

Definition

p680 is a chlorophyll molecule that plays a crucial role in photosynthesis, specifically within photosystem II. This pigment is named for its absorption peak at a wavelength of 680 nanometers, where it captures light energy to initiate the light reactions of photosynthesis, leading to the production of ATP and NADPH.

5 Must Know Facts For Your Next Test

1. p680 is involved in the primary photochemical reaction in photosystem II, where it absorbs light energy and becomes excited.
2. When p680 absorbs light, it loses an electron, which is then transferred to the primary electron acceptor, initiating a series of redox reactions.
3. The oxidation of p680 leads to the splitting of water molecules (photolysis), producing oxygen as a byproduct and releasing protons into the thylakoid lumen.
4. The excited electrons from p680 are passed through the electron transport chain, ultimately leading to the synthesis of ATP and NADPH.
5. p680 is specifically referred to as P680 because it is optimized to absorb light at the red wavelength range, which is important for efficient energy capture during photosynthesis.

Review Questions

• How does p680 function within photosystem II during the light reactions of photosynthesis?
  • p680 functions as the primary pigment within photosystem II by absorbing light at a wavelength of 680 nanometers. When light is absorbed, p680 gets excited and loses an electron. This loss triggers a series of reactions, including the transfer of the electron to an electron acceptor, which is essential for initiating the electron transport chain that ultimately produces ATP and NADPH.
• Describe the role of p680 in water splitting during photosynthesis and its importance for plant metabolism.
  • p680's role in water splitting is crucial because it not only provides electrons needed for the continuation of photosynthesis but also produces oxygen as a byproduct. When p680 is oxidized due to losing an electron, it facilitates the splitting of water molecules into oxygen, protons, and electrons. This process maintains a steady supply of electrons for the electron transport chain while also contributing oxygen to the atmosphere, which is vital for aerobic organisms.
• Evaluate how variations in light quality can affect the efficiency of p680 in photosystem II and overall plant productivity.
  • Variations in light quality can significantly impact how efficiently p680 absorbs light and initiates photosynthesis. For instance, if plants receive more blue or red light, which aligns with p680's absorption spectrum, they will perform better due to optimal energy capture. Conversely, insufficient or inappropriate light wavelengths can lead to decreased excitation of p680, resulting in lower electron flow through the transport chain and reduced ATP and NADPH production. This ultimately affects overall plant productivity by limiting their ability to convert carbon dioxide into sugars through the Calvin cycle.

Related terms

Photosystem II:

A complex of proteins and pigments in plants that plays a vital role in the light-dependent reactions of photosynthesis by capturing light energy and transferring it to p680.

Chlorophyll: The green pigment found in plants, algae, and cyanobacteria that is essential for photosynthesis by absorbing light energy.

Electron Transport Chain: A series of protein complexes and other molecules that transfer electrons from electron donors to electron acceptors, leading to the production of ATP during the light reactions.