Question

The reaction centre for PS I and PS II are (a) \(\mathrm{P}_{700}\) and \(\mathrm{P}_{680}\) respectively (b) \(\mathrm{P}_{6 \mathrm{so}}\) and \(\mathrm{P}_{\mathrm{ron}}\) respectively (c) \(\mathrm{P}_{580}\) and \(\mathrm{P}_{700}\) respectively (d) \(\mathrm{P}_{700}\) and \(\mathrm{P}_{s \infty 0}\) respectively

Short answer

(a) P700 and P680 respectively

Step-by-step solution

Understanding the Question

The question is asking us to identify the specific reaction centers for both Photosystem I and Photosystem II used in the photosynthesis process. Photosystem I has the reaction center of P700 and Photosystem II has P680. Each Photosystem is named after the wavelength to which it is most reactive, with Photosystem I being P700 due to its peak absorption at 700 nanometres and Photosystem II being P680 with its peak absorption at 680 nanometres.

Identifying the Correct Option

Taking the information from the first step, we now look for the option that correctly presents the reaction centers for Photosystem I and Photosystem II. Option (a) presents the correct combination: P700 for Photosystem I and P680 for Photosystem II.

Key concepts

Photosystem I

Photosystem I (PS I) is one of the two crucial stages of the light-dependent reactions in photosynthesis. Located in the chloroplasts of plants, algae, and cyanobacteria, PS I captures light to power the synthesis of energy-rich molecules. Its main role is to absorb photons and utilize the energy to drive the transfer of electrons. This process ultimately leads to the generation of NADPH, a vital energy carrier in the plant.

• PS I's peak absorption occurs at approximately 700 nanometres, which is why it is also known as P700.
• It operates downstream of Photosystem II in the electron transport chain.
• PS I contributes to the building of a proton gradient used in ATP synthesis.

PS I is essential for the photosynthetic process, as it uses light energy to produce organic molecules that serve as the energy sources for plant and algal life.

Photosystem II

Photosystem II (PS II) is the first protein complex in the photosynthetic light reactions. It plays an integral role in the electron transport chain by splitting water molecules to release oxygen and electrons. These electrons are crucial for energy production in plants or algae undergoing photosynthesis.

• PS II is named after its reaction center P680, which is most sensitive to light at a wavelength of 680 nanometres.
• This photosystem initiates the light-dependent reactions by absorbing energetic photons.
• It facilitates the transfer of electrons from water molecules, leading to oxygen release—a vital process for life on Earth.

The primary function of PS II is powering the electron transport system and providing the necessary conditions for ATP synthesis.

Reaction Center

The reaction center is a critical component of photosystems, where light energy is converted into chemical energy. In both Photosystem I and II, the reaction center is a complex of proteins and pigments, predominantly chlorophyll, essential for the initial steps of photosynthesis.

• It functions by using light energy to excite electrons to a higher energy level.
• The excited electrons are then transferred to an electron transport chain, enabling the synthesis of ATP and NADPH.
• Each photosystem has a distinct reaction center, with PS I being P700 and PS II being P680.

These centers effectively harness solar energy and initiate the cascade of reactions forming the basis of life-supporting processes in plants.

P700

P700 refers to the specialized chlorophyll molecule located within the reaction center of Photosystem I. Its name signifies the wavelength of light—700 nanometres—at which this chlorophyll absorbs most effectively. This absorption property makes P700 highly efficient in capturing solar energy.

• P700 is pivotal in facilitating the transfer of electrons, driving the synthesis of NADPH.
• It is the core component enabling PS I to play its role in advanced stages of the photosynthetic electron transport chain.
• This designation of P700 underscores the importance of wavelengths in determining the effectiveness of photosystems.

P700 is essential in ensuring that PS I operates effectively, contributing significantly to the overall process of photosynthesis.

P680

P680 represents the primary chlorophyll molecule found in the reaction center of Photosystem II. This name reflects its peak absorption of light at 680 nanometres. As part of the reaction center, P680 plays a crucial role in photosynthesis by enabling Photosystem II to open the pathway for electron transport via water-splitting.

• P680 captures light energy efficiently to initiate the photolysis of water, resulting in oxygen release.
• It enables the transfer of electrons that eventually progress to Photosystem I.
• Via the establishment of a chemiosmotic gradient, P680 aids in powering ATP synthase, driving ATP production.

P680 marks the starting point for converting light energy into a chemical form usable by organisms, thus supporting multiple life processes.