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Photosynthesis in Higher Plants

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Photosynthesis - An Introduction

We all have learnt in our junior classes about photosynthesis. It is a method which helps plants to prepare their food by themselves. It is one of the most important processes and our food and life also depends on this. But do you know how photosynthesis occurs in higher plants? How is it different from normal photosynthesis?

In this article, we are going to understand the process of photosynthesis in higher plants, reaction of photosynthesis, steps of photosynthesis and full process of photosynthesis.

Definition of Photosynthesis

The process by which green plants, in the presence of light, combine water and carbon dioxide to form carbohydrates is termed as photosynthesis. It occurs in green parts of the plant, mostly the leaves, sometimes the green stems and floral buds. The leaves contain specialised cells called mesophyll cells which contain the chloroplast– the pigment containing organelle. These are the actual sites for photosynthesis.

Structure of a Leave Cell

Structure of a Leave Cell

What is Photosynthesis in Biology?

In Biology, photosynthesis is defined as the process by which green plants, in the presence of light, combine water and carbon dioxide to form carbohydrates. Oxygen is released as a by-product of photosynthesis.

Steps of Photosynthesis

The steps of photosynthesis are explained below:

Step-1 Green plants possess the green pigment, chlorophyll which can capture, transform, translocate and store energy that is readily available for all forms of life on this planet.

Step-2 Photosynthesis is a process in which light energy is converted into chemical energy.

Step-3 Except green plants, no other organism can directly utilise solar energy to synthesise food, hence they are dependent on green plants for their survival.

Step-4 Green plants which can prepare organic food from simple inorganic elements are called autotrophic while all other organisms which cannot prepare their own food are called heterotrophic.

Step-5 During photosynthesis, oxygen liberated into the atmosphere makes the environment livable for all aerobic organisms.

Step-6 Simple carbohydrates produced in photosynthesis are transformed into lipids, proteins, nucleic acids, and other organic molecules.

Step-7 Plants and plant products are the major food sources of almost all organisms on the earth.

Step-8 Fossil fuels like coal, gas, and oil represent the photosynthetic products of the plants belonging to early geological periods.

Photosynthesis in Higher Plants

Photosynthesis is a method which helps plants to prepare their food by themselves. It is considered as one of the most essential processes on earth which is responsible for the existence of human beings and almost all other organisms.

In higher plants, the process of photosynthesis can be explained through two processes, which are light reactions and dark reactions. Now, let's understand what is a light reaction and what is a dark reaction.

Light Reaction

Photosynthesis begins with the light reactions. During this reaction, the energy from the sun is absorbed by the pigment chlorophyll within the thylakoid membranes of the chloroplast. The energy is then quickly transferred to two molecules, ATP and NADPH, which are utilised in the second stage of the chemical process. ATP and NADPH are generated by 2 electron transport chains. During the light reactions, water is used and O2 is formed. These reactions can only occur during daylight because the process needs sunlight to start.

Dark Reaction

Dark reaction is additionally referred to as carbon-fixing reaction. It's a light-independent process within which sugar molecules are formed from the CO2 and water molecules.

The dark reaction occurs within the stroma of the chloroplast, where they utilise the products of the light reaction.

Plants capture the CO2 from the atmosphere through stomata and proceed to the Calvin cycle.

In the Calvin cycle, the ATP and NADPH formed throughout the light reaction drive the reaction and convert six molecules of CO2 into one sugar molecule, i.e. glucose.

Reaction of Photosynthesis

Photosynthesis is the process by which green plants, in the presence of sunlight, combine water and CO2 to make carbohydrates. O2 is formed as a by-product of a chemical process.

Photosynthesis is represented by the following overall chemical equation:

6CO2 + 12H2O → C6H12O6 + 6H2O + 6O2

Interesting Facts

  • Plants perform photosynthesis in organelles called chloroplasts.

  • Chlorophyll isn't a single pigment molecule, but rather is a family of connected molecules that share an analogous structure. These squares measure different pigment molecules that absorb/reflect completely different wavelengths of light.


Photosynthesis is the most vital process on earth without which the existence of human beings and most other living organisms is not possible. It's a process by which green plants, algae and chlorophyll containing microorganisms utilise the energy of sunlight to synthesise their own food (organic matter) from simple inorganic molecules.

The oxidation of organic compounds releases stored energy which is used by the living organisms to carry out essential metabolic processes. It's important to note that photosynthesis is the only natural process that liberates oxygen which is used by all living forms for the process of aerobic respiration.

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FAQs on Photosynthesis in Higher Plants

1. What is phosphorylation?

The formation of ATP within the presence of sunlight is termed photophosphorylation. It is of 2 types: Non-cyclic photophosphorylation and Cyclic photophosphorylation. The photophosphorylation process which results in the movement of the electrons in a non-cyclic manner for synthesising ATP molecules using the energy from excited electrons provided by photosystem II is termed non-cyclic photophosphorylation. Cyclic Photophosphorylation could be a process of photophosphorylation in which an electron expelled by the excited photocentre is returned back to it after passing through a series of electron carriers.

2. What is the C4 cycle?

C4 Cycle (Hatch and Slack Pathway) is a cyclic pathway. The enzymes concerned with the C4 pathway are placed within the Mesophyll cells and Bundle Sheath cells. During this pathway, the plants convert atmospheric CO2 into a four carbon-containing chemical compound. The reaction is mediated by phosphoenolpyruvate carboxylase. After this, aspartic acid and malic acid are formed within the mesophyll cells and transported to the bundle sheath cells within which  the C4 acids break down to release three-carbon molecules and CO2 and further gets converted to phosphoenolpyruvate and complete the cycle.

3. What are the different steps involved in the Calvin Cycle?

The Calvin Cycle is additionally called the C3 cycle or light-independent or dark reaction of photosynthesis. The various stages of the Calvin Cycle or C3 cycle are carbon fixation, reduction, and regeneration. CO2 binds to RuBP in the key method referred to as carbon fixation, forming two-three carbon molecules of phosphoglycerate. Reduction is the second stage of the Calvin cycle. The 3-PGA molecules created through carbon fixation are converted into molecules of simple sugar – glucose. Regeneration is the third stage of the Calvin cycle and could be an advanced process that needs ATP.

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