Article:

Photosynthesis:

Photosynthesis is considered one of the basic processes of life operations in plants, algae, and some bacteria, whereby light energy is transformed into chemical energy in the form of glucose. The important procedures that happen in plants found on the land is photosynthesis. It helps plants to change sunlight into energy. It is a process in which light energy carried by chlorophyll pigments in the leaves is used to bring about a chemical change of carbon dioxide and water into carbohydrates and oxygen. The overall equation for photosynthesis can be represented as:

Figure: (Plant absorbing sunlight)

Equation:

6CO2 + 6H2O + light energy = C6H12O6 + 6O2

This process is crucial for the life cycle of plants; through this process, the seeds are provided with the energy required to grow and produce more seeds. Moreover, photosynthesis is also a vital stage in the process of the atmosphere’s carbon conversion, as it includes the removal of CO2 and the production of the oxygen necessary for life.

Factor affecting Photosynthesis:

1.      Sunlight:

This shows that the amount of light or solar. These radiations are pivotal open factors that control photosynthesis in most terrestrial plants. ‘Photosynthesis’, is the process of using energy from light to convert water and carbon dioxide into food. It is the main energy process carried out by plants and requires an amount of light to do this work effectively. These include factors like the flow of the light, the duration in which light falls, and even the quality of the light which may be either high or low. Light is required to eject electrons from the metal elements such as potassium, zinc, and sodium. These electrons then take part in the electron transport chain of light-dependent reactions. However, the ejection of electrons depends upon the wavelength of light.

2. Carbon dioxide:

Carbon dioxide is another factor that limits photosynthesis in terrestrial plants. Lab exercise reports another important factor that impacts photosynthesis in terrestrial plants is the level of carbon dioxide. Carbon is fixed in the Calvin cycle of the photosynthesis process, and plants should have enough of this gas to produce glucose. For aquatic plants, carbon dioxide is dissolved in the water that they can use in photosynthesis.

3. Water:

For photosynthesis of plants grown on land, water is as important as light and carbon dioxide. It rises through the plant stems and reaches leaves, where it is utilized for synthesis of various products including food. Some works involve the influence of variables including the soil water content and the plant vascular system to regulate the rate of photosynthesis.

4. Pigments:

Pigments that are used in photosynthesis are Chlorophylls, phycobilin, and carotenoid. Chlorophyll a and Chlorophyll b and c are used in photosynthesis. All eukaryotes have Chlorophyll which is used for oxygen-generating photosynthesis. Chlorophyll b is present in plants, and algae and is use to broaden the range of light in photosynthesis. In brown algae, chlorophyll c is present in place of chlorophyll b and performs the function of chlorophyll b.

 Phases of Photosynthesis:

The process of photosynthesis can be divided into two main phases: As the name suggests the two stages are known as light-dependent reaction and light-independent reaction. During light-dependent reactions, light energy is in the form of light passed by the chlorophyll molecules in the chloroplasts. The plant cell uses it to split water molecules into oxygen and hydrogen ions. It forms ATP a molecular machine that stores energy for utilization in the future.

The light-independent or the dark reactions involve the formation of carbohydrates especially glucose from the CO2 using ATP and hydrogen ions generated in the light-dependent reactions or the Calvin cycle. It is a sequence of various chemical reactions that occur under the catalytic impact of enzymes and yield glucose, the substance required by plants to produce energy and it can be accumulated.

  

                                                              Figure no. 1: (Light-dependent reaction)

Light Reaction:

Where It Happens:

These reactions occur at an organelle called chloroplasts where the membranes are folded creating compartments known as thylakoids.

Key Players:

Photosystems: These are complexes formed of proteins and pigments such as chlorophyll that trap light energy, which is used to drive photosynthesis. Each photosystem has a reaction center and an antenna complex and contains 250 to 400 pigment molecules. Antenna complexes have pigment molecules and reaction centers have chlorophyll and protein. Photosystems are linked by the electron transport chain.

• Photosystem I (PSI):

It carries a special pair of chlorophyll molecules known as P700. The P is for pigment and 700 for absorption peak.

• Photosystem II (PSII):

It can come with a specific pair of chlorophyll molecules known as P680. The P stands for pigment and 680 is its absorption peak.

• Process Overview:

Light Absorption in PSII:

This energy is then transferred to the core of PSII through the antennae pigments excites the molecule and releases the electron transferred to the electron transport chain. The gap of electrons in Photosystem II is recovered by absorbing 4 photons of light that split the water molecule which releases four protons, four electrons, and an oxygen molecule. This splitting of water molecules establishes a proton gradient which generates ATP molecules.  

Electron Transport Chain:

This occurs as electrons transfer from PSII to PSI. The electron transport chain contains Plastocyanin, Cytochromes, Plstoquinone, and Pheophytin. The proton gradient established in Photosystem II is then transferred to the electron transport chain and becomes an electrochemical proton gradient used to generate ATP synthesis. This proton gradient moves downward into the stroma of chloroplast due to the ATP synthase enzyme.

Photosystem I

In photosystem I energy is transferred when light falls on the antenna molecules. Energy is then transferred to the reaction center. Electrons are energized and transferred to primary acceptor A₀ similar to Pheophytin. Electrons are moved downwards and transferred to phyllo Quinone iron Sulfur proteins. At last reduction of NADP to NADPH occurs. The electron gap in photosystem I is filled by the electron of the electron transport chain.

Two photons of light are absorbed by photosystem I and two photons of light are absorbed by photosystem II to reduce NADP to NADPH and to synthesize ATP molecules from the breakdown of water molecules.

            H₂O + NADP⁺ → NADPH + H⁺ + ½ O₂