In this article, we will learn in detail about Photosynthesis Formula. The Sun is, as we all know, the major source of energy for all living things. But do you realise how much we rely on plants for our food? Photosynthesis is the process through which plants absorb the Sun’s energy and utilise it to make food. Let’s learn more about this process, which is essential for all living things to survive.

Photosynthesis is the process by which autotrophs like plants, algae and some microorganisms capture and convert solar energy into chemical energy. This process recycles oxygen into the atmosphere by using carbon dioxide produced by all breathing creatures.

Let us now dive deep into understanding what Photosynthesis Formula is, how it is measured, etc. Continue reading to know more.

Types of Photosynthesis

There are two types of photosynthetic processes.

1. Oxygenic Photosynthesis (primarily seen in plants, algae and cyanobacteria)
2. Anoxygenic Photosynthesis (primarily seen in purple bacteria and green sulfur bacteria)

Oxygenic Photosynthesis 

In this type of Photosynthesis, light energy from the Sun transfers electrons from water \(\left( {{{\rm{H}}_2}{\rm{O}}} \right)\) to carbon dioxide \(\left( {{\rm{C}}{{\rm{O}}_2}} \right)\) to produce carbohydrates. \({\rm{C}}{{\rm{O}}_2}\) is “reduced” or gains electrons during this transfer, and the water becomes “oxidized” or loses electrons. This oxidation-reduction reaction produces oxygen along with carbohydrates.

Oxygenic photosynthesis counterbalances respiration. Respiration involves the production of carbon dioxide by all breathing organisms, whereas Photosynthesis involves reintroducing oxygen to the atmosphere.

Anoxygenic Photosynthesis 

In this, no oxygen is produced as a byproduct and is processed by organisms primarily found in various aquatic habitats.

The overall reaction of Oxygenic Photosynthesis is written as follows:

Here, six molecules of carbon dioxide \(\left( {{\rm{C}}{{\rm{O}}_2}} \right)\) combine with twelve molecules of water \(\left( {{{\rm{H}}_2}{\rm{O}}} \right)\) using light energy to form a single carbohydrate molecule (\({{\rm{C}}_{\rm{6}}}{{\rm{H}}_{{\rm{12}}}}{{\rm{O}}_{\rm{6}}}\) Or glucose). Six molecules of oxygen and water are also produced.

The following components are essential to Photosynthesis:

Pigments

Pigments are molecules that impart colour to plants, algae and bacteria. They are also responsible for trapping sunlight effectively. Pigments of different colours absorb different wavelengths of Light. Among all pigments, the most important one is the green coloured chlorophyll. These pigments are capable of trapping blue and red Light. Chlorophylls are classified into three subtypes – dubbed chlorophyll \({\rm{A}}\), chlorophyll \({\rm{B}}\) and chlorophyll \({\rm{C}}\).

Photosynthesis occurs in the chloroplasts, specifically in the grana and stroma regions. The grana consist of disc-shaped membranes stacked into columns like plates. It is the innermost portion of the organelle. The individual discs are called thylakoids and are responsible for the transfer of electrons. Stroma constitutes the empty spaces between columns of grana.

Antennae

An extensive collection of \(100\) to \(5,000\) pigment molecules constitutes antennae. The function of these structures is to effectively capture light energy from the Sun in the form of photons and transfer it to chlorophyll pigments. The conversion of light energy to chemical energy is complete when a chlorophyll pigment expels an electron and the electron moves to an appropriate recipient.

Reaction centres

Reaction centres are the pigments and proteins that convert light energy to chemical energy and initiate electron transfer.

Chlorophyll \({\rm{A}}\) is the reaction centre, where the energy is trapped. The antenna pigments are mainly chlorophyll \({\rm{B}}\), xanthophylls and carotenoids molecules, which absorb photons and transfer their energy to the reaction centre.

The Photosynthetic Process

The Photosynthesis process is divided into two stages. These are:

Stage 1: Light-dependent stage (also called light reactions )
These reactions require the presence of sunlight and take place in the thylakoid of the chloroplasts.  

When a photon of Light hits the reaction centre, chlorophyll \({\rm{A}}\) is activated, releases an electron and initiates the breakdown of a water molecule into \({{\rm{H}}^ + }\) and \({\rm{O}}{{\rm{H}}^ – }\). This process is known as the photolysis of water.

The “electron-hole” in the original chlorophyll pigment is filled by taking an electron from water.

Each water molecule breaks down into two hydrogens \(\left( {\rm{H}} \right)\) atoms and one oxygen \(\left( {\rm{O}} \right)\) atom. Oxygen atoms from the photolysis of water molecules join up in pairs to form oxygen \(\left( {{{\rm{O}}_2}} \right)\).

The \({{\rm{H}}^ + }\) ions pass through an enzyme called \({\rm{ATP}}\) synthase and provide it with the energy needed to add the third phosphate to \({\rm{ADP}}\) (adenosine diphosphate) to form \({\rm{ATP}}\) (adenosine triphosphate). \({\rm{NAD}}{{\rm{P}}^{\rm{ + }}}\) (Nicotinamide adenine dinucleotide phosphate) joins with these hydrogen ions to create the energy-carrying molecule \({\rm{NADPH}}\).

The aim of the light-dependent reactions of Photosynthesis is to collect energy from the Sun, which is then used to break down water molecules to produce \({\rm{ATP}}\) and \({\rm{NADPH}}\). These two energy-storing molecules are then used to power the light-independent reactions.

Stage 2: Light-independent reactions (also called dark reactions or the Calvin cycle):

The energy sources \({\rm{ATP}}\) and \({\rm{NADPH}}\) produced in light reactions drive dark reactions. These reactions take place in the stroma. The Calvin cycle takes place in three steps:

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Carbon Fixation

This part of the light-independent reaction fixes carbon dioxide \(\left( {{\rm{C}}{{\rm{O}}_2}} \right)\) from the air into building blocks of glucose. An enzyme in the stroma called RuBisCo (Ribulose bisphosphate carboxylase) combines a five-carbon molecule of RuBP (ribulose bisphosphate) with a molecule of carbon dioxide. This creates a six-carbon molecule that is broken down into two three-carbon molecules (\(3\)-phosphoglycerate).

Sugar Reduction

\({\rm{ATP}}\) and \({\rm{NADPH}}\) obtained from light reactions participate in this step. Both \({\rm{ATP}}\) and \({\rm{NADPH}}\) give \(3\)-phosphoglycerate to one hydrogen atom, creating two molecules of the simple sugar \({\rm{G3P}}\) (glyceraldehyde-\(3\)-phosphate). The two molecules of \({\rm{G3P}}\) are used to build one molecule of glucose. As electrons are added, this part of the light-independent reactions is typically referred to as reduction (or reducing the sugar).

Regeneration 

In the Calvin cycle, six molecules of carbon dioxide are involved at a time generating twelve molecules of \({\rm{G3P}}\). However, only two of them are used to produce a glucose molecule—the rest are recycled back into \({\rm{RuBP}}\) to keep the Calvin cycle running. The ultimate goal of the light-independent reactions (or Calvin cycle) is to assemble a glucose molecule.

Light-dependent Reactions

Goal	Convert light energy into chemical energy
Location	Chloroplasts – thylakoids
Input	Sunlight, \({{\rm{H}}_{\rm{2}}}{\rm{O}},\,{\rm{NAD}}{{\rm{P}}^{\rm{ + }}},\,{\rm{ADP}}\)
Output	\({\rm{NADPH, ATP,}}\,{{\rm{O}}_2}\)

Light-independent Reactions

Goal	Use stored chemical energy to “fix” \({\rm{C}}{{\rm{O}}_2}\) and create a product that can be converted into glucose
Location	Chloroplasts – stroma
Input	\({\rm{C}}{{\rm{O}}_2}{\rm{, NADPH, ATP}}\)
Output	\({\rm{NAD}}{{\rm{P}}^ + },\,{\rm{ADP}},\,{\rm{G3P}}\) (Two \({\rm{G3P}}\) can be made into \({{\rm{C}}_6}{{\rm{H}}_{12}}{{\rm{O}}_6}\))

Summary

Photosynthesis is the basic cycle of all processes responsible for the survival of organisms on the earth. It is not only essential from the food point of view but also in maintaining the ecological balance of nature. Hence, we must learn about the reactions that take place in it. In this article, we discussed Photosynthesis, Light-dependent and light-independent reactions, and the overall formula of the process.

FAQs

We have provided some frequently asked questions about Photosynthesis Formula here:

Q.1. What is Photosynthesis for kids?
Ans: Photosynthesis is the process in which green plants traps sunlight and use it to make their food. It requires sunlight, chlorophyll, water, and carbon dioxide gas. Chlorophyll traps energy from sunlight, and plants use this light energy to change water and carbon dioxide into oxygen and sugars. The plants use some of the sugars and store the rest. The oxygen is released into the air.

Q.2. Why is the Calvin cycle called a dark reaction?
Ans: Photosynthesis takes place in two stages – Light-dependent reaction stage and Light independent or dark reaction stage. The dark reaction stage is also known as the Calvin cycle. Light is not required in this stage of the photosynthesis process, hence the name dark reaction. Light is only required in the Light-dependent reaction stage of the photosynthesis process.

Q.3. Is Photosynthesis a balanced equation?
Ans: Yes, Photosynthesis is a balanced equation which is as follows-

Q.4. What is Photosynthesis? Explain with the balanced equation?
Ans: Photosynthesis is the process by which plants, in the presence of chlorophyll trap the energy of the Sun, absorb water, and carbon dioxide to produce oxygen and energy in the form of sugar. The balanced chemical equation is as follows:

Q.5. Why is \({\rm{12}}{{\rm{H}}_{\rm{2}}}{\rm{O}}\) used in Photosynthesis?
Ans: The net reaction of Photosynthesis is :

From the above reaction, to form one molecule of glucose, six carbon dioxide molecules are required. In dark reactions to form one molecule of glucose, \(12\) molecules of \({\rm{NADPH}}\) and \(18\) molecules of \({\rm{ATP}}\) are required. \({\rm{NADPH}}\) is formed when \({\rm{NAD}}{{\rm{P}}^ + }\) combines with \({{\rm{H}}^ + }\) ions. Each molecule of water dissociates into \({{\rm{H}}^ + }\) and \({\rm{O}}{{\rm{H}}^ – }\) ions. Hence, to produce \(12\) molecules of \({\rm{NADPH,}}\,{\rm{12}}\) molecules of water are required.

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