What is photosynthesis?
It involves the process in which the light energy (particularly from the sunlight) is converted into some biochemical energy such as glucose followed by the release of oxygen, in few bacteria, plants and algae.
Factors involved in photosynthesis:
The factors involved in photosynthesis include water, nutrients, carbon-di-oxide, sunlight, minerals and chlorophyll.
Water:
The absorption of water takes place through the roots. It provides hydrogen ions and electrons for the photosynthesis to occur. It also functions as a medium that transports the other nutrients.
Nutrients:
There are several micro and macronutrients that support the process of photosynthesis. The micro-nutrients include boron, iron, zinc, copper, molybdenum, manganese and chlorine. The macro-nutrients include Phosphorus, Calcium, Magnesium, Nitrogen, Sulphur and Potassium.
Micro-nutrients:
Boron:
It is important for the formation of cell walls, transport of sugar and regulation of hormones.
Iron:
It is essential for the process of photosynthesis and the capturing of sunlight takes place through this pigment.
Zinc:
It is necessary for the synthesis of the protein, function of the enzyme and plant hormone production such as auxin that is involved in growth regulation.
Copper:
It plays the role of catalyst in respiration and photosynthesis and produces lignin to contribute as structural support to the plant cells.
Molybdenum:
It is a part of an enzyme that is usually involved in the fixation of nitrogen primarily, metabolism of the nitrogen.
Manganese:
It is a part of an oxygen evolving complex in photosynthesis which is helpful in splitting the water molecules in the photosynthesis reactions that are light dependent.
Chlorine:
Its original function is not known but it seems to be involved in the process of photosynthesis and osmotic regulation.
Macro-nutrients:
Phosphorus:
It is important for the development of the root, seed and flower production and is also involved in RNA and DNA synthesis.
Calcium:
It is involved in cell wall strengthening, activation of the enzyme and helps in cell division.
Magnesium:
It is crucial for activation of the enzymes.
Nitrogen:
It plays an essential role in the synthesis of chlorophyll and is important for enzyme and protein production.
Sulphur:
It is a part of various proteins and enzymes and is involved in the activation of the enzymes.
Potassium:
It is involved in activation of the enzymes, plays a main role in photosynthesis and carbohydrate and protein synthesis.
Two stages of photosynthesis
The two stages of photosynthesis include light independent and light dependent reactions. One common step involved in both the stages of photosynthesis is phosphorylation.
Note: Phosphorylation:
It involves the formation of ATP molecules using light energy in light dependent reactions. Its occurrence happens in the chloroplast's thylakoid membrane. But, in the light independent reactions of the photosynthesis, the 3-PGA molecules are converted to 1,3-Bisphosphoglycerate with the help of the ATP produced in the light dependent reactions of photosynthesis. This process is known as phosphorylation as it involves the use of phosphoglycerate kinase to reduce 3-PGA to G3P.
Light independent reactions:
It takes place in the space around the thylakoids i.e. stroma, in the chloroplast. It involves the conversion of carbon dioxide into glucose using NADPH and ATP. It is also called the Calvin cycle. It is divided into three stages namely carbon fixation, reduction and regeneration.
Carbon fixation:
The enzyme RuBisCo catalyzes the reaction which incorporates carbon-di-oxide into a five-carbon compound or sugar, Ribulose-1,5-bisphosphate (RuBP). Then the breakdown of the six carbon compounds into two molecules of 3-PGA (3-Phosphoglycerate).
Note: RuBisCo is also involved in the oxygenase activity, which is nothing but photorespiration. Photorespiration is the process in which RuBisCo binds to oxygen when the carbon-di-oxide levels are low. Increased temperature or dry and hot conditions also favour photorespiration. The C3 plants like wheat, rice, soybeans etc., straightforwardly fix the carbon-di-oxide in the calvin cycle, thereby increasing the photorespiration. Whereas, C4 plants like corn, sugarcane, sorghum etc., and CAM plants like cacti, succulents, pineapple etc., reduce the photorespiration by separating the carbon fixation and calvin cycle or by the fixation of carbon during night and using it in the day. One of the major anatomy used by C4 plants to reduce photorespiration is Kranz anatomy which involves the ring formation of carbon dioxide molecules around the enzyme RuBisCo.
Reduction:
The conversion of 3-PGA into Glyceraldehyde-3-Phosphate (G3P) takes place. It is the combination of phosphorylation in which ATP is utilized and reduction in which NADPH is used. The production of six molecules of G3P takes place for every three molecules of carbon-di-oxide utilized. The five molecules of G3P stay in the cycle for the regeneration of the RUBP but the one molecule of G3P leaves the cycle for glucose or other carbon compounds biosynthesis.
Regeneration:
The five molecules of G3P which stayed in the cycle are used to regenerate the RUBP molecules. It utilizes the ATP and various enzymatic reactions.
Light dependent reactions:
It occurs within the chloroplasts in the thylakoid membrane. They usually need water and sunlight. It involves the process of converting the absorbed light energy by some pigments and chlorophyll into chemical energy as NADPH and ATP. The release of the byproduct oxygen takes place when the molecule of the water is split. The photosystem II (PSII), electron transport chain (ETC) and photosystem I (PSI) are the major components of light dependent reactions in photosynthesis.
Photosystem II (PSII):
The PSII reaction center is called P680 as it absorbs the light well in the wavelength of 680nm. It is located in the thylakoid membrane of the chloroplast. It utilizes the light energy to break down the water molecules to release oxygen and energize the electrons which are later transported to ETC.
Electron Transport Chain (ETC):
The transfer of electrons to PSI from PSII takes place here using several protein complexes. As the electrons travel through the chain, the protons are pumped out of the stroma into the thylakoid lumen, contributing to a proton gradient.
Photosystem I (PSI):
It is also found in the thylakoid membrane of the chloroplast. The PSI has its reaction center at a wavelength of 700 nm and hence it is named P700. Its primary function is to energize the electrons transferred along the ETC with the help of light energy. The reduction of NADP to NADPH also takes place here.
Importance of photosynthesis:
The significance of photosynthesis include production of food, maintaining the balance of the ecosystem, carbon cycle, production of biofuels and production of the energy source and oxygen.
Production of food:
It is the ultimatum of the energy source among the living organisms as they produce their own food with the help of water, carbon dioxide and sunlight. This forms the base for all the living organisms as they depend on plants either directly or indirectly for the source of energy and nutrients.
Maintaining the balance of the ecosystem:
It helps in maintaining the balance of the ecosystem as it consumes the greenhouse gas which is nothing but carbon dioxide, released into the world and produces oxygen, which is essential for the survival of the animals and human beings.
Carbon cycle:
The photosynthesis process is the major part of the carbon cycle as it involves the movement of carbon dioxide between oceans, atmosphere and land. It regulates the carbon dioxide levels in the earth or atmosphere.
Production of biofuels:
Genetic engineering approaches are used to elevate the efficiency of photosynthesis. One such example is modifying the traits of cyanobacteria and algae to produce biofuels and other useful chemical compounds.
Production of the energy source:
Photosynthesis involves the production of the energy source which is essential for all the living organisms on the earth. It forms the glucose which is the chemical energy consumed by most of the living organisms on earth.
Production of the oxygen:
Photosynthesis produces oxygen and it is the primary source of energy required by all the organisms on earth for respiration. Without the production of oxygen, life on earth is almost equal to impossible.
Environmental impact in photosynthesis:
The environmental factors such as change of climate like drought, extreme temperatures and salinity and pollution negatively affect the photosynthesis rate. While, other factors like light intensity, enrichment of Carbon-di-oxide positively affect the rate of photosynthesis
