Chloroplasts

Plants form the basis of all life on earth and are known as producers. Plant cells contain structures known as plastids which are absent in animal cells. These plastids are double-membraned cell organelles which play a primary role in the manufacturing and storing of food. There are three types of plastids –

  • Chromoplasts- They are the colour plastids, found in all flowers, fruits and are mainly responsible for their distinctive colours.
  • Chloroplasts- They are green coloured plastids, which comprises of green-coloured pigments within the plant cell and are called as the chlorophyll.
  • Leucoplasts- They are colourless plastids and are mainly used for the storage of starch, lipids, and proteins within the plant cell.

Also Read: Plastids

Chloroplasts

Plants, especially the green ones prepare their own food by a process called photosynthesis. They are therefore known as autotrophs and primary producers in the food web. All green plants comprise a specialized structure known as chloroplast, and the green pigments called chlorophyll within the cell and are responsible for the synthesis of food.

Also Read: Photosynthesis

Chloroplast Structure

Chloroplasts are found in all higher plants. They are oval or biconvex shaped, cell organelles found within the mesophyll of the plant cell. The size of the chloroplasts organelle usually varies between 4-6 µm in diameter and 1-3 µm in thickness. They are double-membrane organelle with the presence of outer, inner and the thin intermembrane space present in between the two layers. There are two distinct regions present inside the chloroplasts and are called as the grana and stroma.

  • Grana is made up of stacks of disc-shaped structures known as thylakoids. The grana of the chloroplast consist of chlorophyll pigments and are the functional units of chloroplasts.
  • Stroma is the homogenous matrix which contains grana and is similar to the cytoplasm in cells in which all the organelles are embedded. Stroma also contains various enzymes, DNA, ribosomes, and other substances. Stroma lamellae function by connecting the stacks of thylakoid sacs.

 

Chloroplast

Parts of Chloroplasts

  • Outer membrane –It is a semi-porous, permeable membrane.
  • Inner membrane – The inner membrane of the chloroplast forms a border to the stroma. It regulates the passage of materials in and out of the chloroplast. In addition to regulation activity, fatty acids, lipids, and carotenoids are synthesized in the inner chloroplast membrane.
  • Intermembrane Space – It is a thin membrane, present between the outer and the inner membrane of the chloroplast.
  • Stroma- It is a colourless, alkaline, aqueous, protein-rich fluid present within the inner membrane of the chloroplast present surrounding the grana.
  • Thylakoid System- The system is suspended in the stroma. It is a collection of membranous sacs called thylakoids. The green coloured pigments called chlorophyll are found in this thylakoids membrane. It is the sight for the process of light-dependent reactions of the photosynthesis process. The thylakoids are arranged in stacks known as grana and each granum contains around 10-20 thylakoids.

Also read: Light-dependent Reactions

Chloroplasts Functions

  • The most important function of the chloroplast is to synthesis food by the process of photosynthesis.
  • Absorbs light energy and converts into biological energy.
  • Chloroplasts have a structure called chlorophyll which functions by trapping the solar energy and used for the synthesis of food in all green plants.
  • Produces NAPDH2 and molecular oxygen(O2) through the process of photolysis of water.
  • Produces ATP – Adenosine triphosphate by the process of photophosphorylation.
  • Transfers carbon dioxide (CO2) obtained from the air into carbon and sugar during the Calvin Cycle or dark reaction of photosynthesis.

Also Refer: Calvin Cycle

Important Questions on Chloroplasts

  • Where does the photosynthesis process occur in the Plant cell?

In all green plants, photosynthesis- a biological process takes place within the thylakoid membrane of the Chloroplasts.

  • List out the different parts of Chloroplasts?

Chloroplasts are cell organelles present only in a plant cell and it includes:

  1. Stroma
  2. Inner membrane
  3. Outer membrane
  4. Thylakoid membrane
  5. Intermembrane Space.

Learn more about the Chloroplast, its structure, functions, and other Cell organelles @  BYJU’S Biology

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