What Is Photosynthesis?

“Photosynthesis is the process used by green plants and a few organisms that use sunlight, carbon dioxide and water to prepare their food.”

The process of photosynthesis is used by plants, algae and certain bacteria that convert light energy into chemical energy. The glucose formed during the process of photosynthesis provides two important resources to organisms: energy and fixed carbon.

Read on to explore what is photosynthesis and the processes associated with it.

Site of Photosynthesis

Photosynthesis takes place in special organelles known as chloroplast. This organelle has its own DNA, genes and hence can synthesize its own proteins. Chloroplasts consist of stroma, fluid, and stack of thylakoids known as grana. There are three important pigments present in the chloroplast that absorb light energy, chlorophyll a, chlorophyll b, and carotenoids.

Also Read: Photosynthesis Process

Types of Photosynthesis

There are two different types of photosynthesis:

  • Oxygenic photosynthesis
  • Anoxygenic photosynthesis

Oxygenic Photosynthesis

Oxygenic photosynthesis is more common in plants, algae and cyanobacteria. During this process, electrons are transferred from water to carbon dioxide by light energy, to produce energy. During this transfer of electrons, carbon dioxide is reduced while water is oxidized, and oxygen is produced along with carbohydrates.

During this process, plants take in carbon dioxide and expel oxygen into the atmosphere.

This process can be represented by the equation:

6CO2+ 12H2O + LIGHT ENERGY → C6H12O6 + 6O2 + 6H2O

Anoxygenic Photosynthesis

This type of photosynthesis is usually seen in certain bacteria, such as green sulphur bacteria and purple bacteria which dwell in various aquatic habitats. Oxygen is not produced during the process.

The anoxygenic photosynthesis can be represented by the equation:

CO2 + 2H2A + LIGHT ENERGY → [CH2O] + 2A + H2O

Also Read: Difference between Photosynthesis and Respiration

Photosynthesis Apparatus

The photosynthesis apparatus includes the following essential components:


Pigments not only provide colour to the photosynthetic organisms, but are also responsible for trapping sunlight. The important pigments associated with photosynthesis include:

  • Chlorophyll: It is a green-coloured pigment that traps blue and red light. Chlorophyll is subdivided into, “chlorophyll a”, “chlorophyll b”, and “chlorophyll c”. “Chlorophyll a” is widely present in all the photosynthetic cells. A bacterial variant of chlorophyll known as bacteriochlorophyll can absorb infrared rays.
  • Carotenoids: These are yellow, orange or red-coloured pigments that absorb bluish-green light. Xanthophyll and carotenes are examples of carotenoids.
  • Phycobilins: These are present in bacteria and red algae. These are red and blue pigments that absorb wavelength of light that are not properly absorbed by carotenoids and chlorophyll.


Plastids are organelles found in the cytoplasm of eukaryotic photosynthetic organisms. They contain pigments and can also store nutrients. Plastids are of three types:

  • Leucoplast: These are colourless, non-pigmented and can store fats and starch.
  • Chromoplasts: They contain carotenoids.
  • Chloroplasts: These contain chlorophyll and are the site of photosynthesis.


Antennae is the collection of 100 to 5000 pigment molecules that capture light energy from the sun in the form of photons. The light energy is transferred to a pigment-protein complex that converts light energy to chemical energy.

Reaction Centers

The pigment-protein complex responsible for the conversion of light energy to chemical energy forms the reaction centre.

Also Read: Photosynthesis

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