Question

In cyclic photophosphorylation, the electron released by reaction centre \(\left(P_{700}\right)\) is ult?mately accepted by (a) ferredoxin (b) \(\mathrm{NADP}^{+}\) (c) reaction centre \(\left(P_{700}\right)\) (d) plastocyanin.

Short answer

The electron released by reaction centre \(P_{700}\) is ultimately accepted by (c) reaction centre \(P_{700}\).

Step-by-step solution

Understanding The Concept

Cyclic photophosphorylation refers to the process in photosynthesis where an electron is excited by light in the photosystems, and then passes through a series of carriers and eventually returns to the original chlorophyll molecule. This process generates ATP without the production of NADPH or the evolution of oxygen.

Identify the Participants in Cyclic Photophosphorylation

Within cyclic photophosphorylation, after being excited at the reaction center \(P_{700}\), the electron goes through several electron carriers including ferredoxin (Fd), the cytochrome b6f complex, and plastocyanin (Pc), before it returns to \(P_{700}\).

Determine the Ultimate Acceptor of the Electron

The electron that is initially released by the \(P_{700}\) reaction center is ultimately accepted by the reaction center \(P_{700}\) itself, as the process is cyclic and the electron returns to its starting point.

Key concepts

Photosynthesis

Photosynthesis is the remarkable biological process by which plants, algae, and certain bacteria convert light energy into chemical energy, using it to fuel their growth and survival. At its core, it involves the absorption of light by pigments in the plant, primarily chlorophyll, which is housed within chloroplasts.

During this process, light energy is captured and used to convert carbon dioxide (CO2) from the atmosphere and water (H2O) from the soil into glucose, a sugar that serves as an energy source for the organism. One of the byproducts of this synthesis is oxygen (O2), which is released into the atmosphere. Photosynthesis not only sustains the life of the plant itself but also provides the base energy source for virtually all other organisms on Earth.

Electron Transport Chain

The electron transport chain is a series of protein complexes and other molecules that transfer electrons from electron donors to electron acceptors via redox reactions. This chain is used in both photosynthesis and cellular respiration to generate energy.

In photosynthesis, the electron transport chain is responsible for converting the energy from sunlight into a more useable form - ATP and NADPH, which are essential for the Calvin cycle that synthesizes sugars. As electrons are excited by sunlight and pass through the chain within the thylakoid membrane of chloroplasts, they release energy that is harnessed to pump protons and produce ATP in a process known as chemiosmosis.

Chlorophyll Molecule

Chlorophyll is the green pigment found in virtually all photosynthetic organisms. It's vital for its role in absorbing light energy and initiating the process of photosynthesis.

There are different types of chlorophyll, with chlorophyll a being the primary pigment. It has a unique structure that allows it to anchor in the thylakoid membrane and absorb light most efficiently in the red and blue spectra. The excitation of a chlorophyll molecule by light is the trigger for a series of electron transfers, which constitutes the beginning of the photosynthetic electron transport chain.

ATP Generation

ATP, or adenosine triphosphate, is the energy currency within biological systems. In photosynthesis, ATP is synthesized during the light-dependent reactions through a process called photophosphorylation.

There are two types of photophosphorylation: non-cyclic and cyclic. In cyclic photophosphorylation, as in the exercise we are discussing, electrons are cycled back to the chlorophyll molecule and not used to produce NADPH. The key purpose here is the creation of ATP as the electrons flow through the electron transport chain, generating a proton gradient across the thylakoid membrane and powering ATP synthase to attach a phosphate group to ADP, forming ATP. This ATP will later be used in the Calvin cycle, the next stage of photosynthesis, where carbon fixation occurs, leading to the synthesis of sugars.