Difference Between Photosystem 1 And Photosystem 2: Explanation, Types, Steps And FAQs

Photosystem Definition

Photosystems are the pigment-protein complexes located in the thylakoid membranes of chloroplasts. They play a riding role in light-dependent reactions of photosynthesis by capturing and then converting light energy into chemical energy. There are two types of photosystems: Photosystem 1 and Photosystem 2, which differ in their function and composition.

Photosystems are embedded in the thylakoid membranes of chloroplasts and play a critical role in capturing the energy from light to drive electron transport, which results in the formation of ATP and NADPH. These are products essential for the Calvin cycle and glucose synthesis in plants.

The very knowledge of photosystems is the most important topic for any student from Class 9 until the undergraduate NEET students. Photosystems are a very basic concept both in plant biology and bioenergetics. The significance of photosystems is not only associated with their role in the mechanism of photosynthesis but has far-reaching applications in bioengineering or biological engineering projects like artificial photosynthesis in research, photovoltaic systems development for renewable energy, etc.

Structure Of Photosystems

• The structure of photosystems is so complex and so highly specialised that they talk about the capture and conversion of light energy to the extreme.

• Each photosystem is the optimal structure for carrying out the light-involving reactions as well as absorbing the light it needs during its particular range of wavelengths.

• A photosystem consists of a reaction centre chlorophyll where the primary light-induced credit to the electron transport chain originates. It is connected to an antenna complex.

Photosystem 1 (PSI)

• Reaction center chlorophyll: P700.

• Core antenna complex: 6 to 25 chlorophyll molecules and several proteins called the core antenna complex.

• Primary electron acceptor: its primary electron acceptor is an iron-sulfur protein.

• Location: The PSI is located in the membranes of the thylakoids.

Photosystem II (PSII)

• Reaction Center Chlorophyll: P680

• Core Antenna Complex: There is significant variation in the chlorophyll and carotenoid pigments.

• Primary Electron Acceptor: Plastoquinone.

• Oxygen-Evolving Complex: Salt in the path, which is responsible for water-splitting and evolution of oxygen.

• Site: Thylakoid membrane, across the stack of grana.

Table: Difference Between PSI And PSII

Functions Of Photosystems

Role in Light-dependent Reactions

Photosystem 1 (PSI)

• It absorbs light energy of wavelength 700 nm.

• Transfers electrons to ferredoxin

• Participates in generating NADPH

Photosystem 2 (PSII)

• It absorbs light energy of wavelength 680 nm

• Splits H2O molecules to release oxygen

• Transfers electrons to plastoquinone

• Participates in generating ATP.

Detailed Mechanism Of Action

The electron transport chain of photosystems is a cascade of redox steps that process light energy, eventually converting it into the chemical energy in the coenzymes ATP and NADPH.

Photosystem I (PSI)

• Absorption of light by P700.

• Excitation of electrons and transfer of the same to the primary acceptor.

• Subsequent transport of electrons to ferredoxin.

• Catalysation of the formation of NADPH by the enzyme ferredoxin-NADP+ reductase.

Photosystem II (PSII)

• Absorption of light by P680.

• Oxygen and protons are released.

• Electrons donated to plastoquinone and passed to cytochrome b6f complex.

Photosystems 1 And 2 In Different Organisms

Photosystems may have slight variations from one type of plant to the other, making some more efficient or compatible with certain environments than others.

Variations Across Various Plant Species

• C3 Plants: Normal structure and functioning of PSI and PSII.

• C4 Plants: More efficient photosynthesis in high-temperature environments by way of adaptations.

• CAM Plants: Temporal separation of the activity of PSI and PSII to avoid water loss.

Influence Of Photosynthetic Efficiency On Overall Photosynthesis

• The efficiency of PSI and PSII influences the rate at which ATP and NADPH are produced.

• Differences in this respect can lead to differences in growth and in the ability to adapt to environmental conditions.

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