Chloroplasts-Definition, Structure, Functions, And Diagram

Chloroplasts Definition

  • The name “chloroplast” has its roots in the Greek words chloros, which means “green,” and plastes, chloroplast indicates “the one who produces.”
  • The chlorophyll-containing photosynthetic pigment is housed in chloroplasts, a subtype of membrane-bound plastids that have a complex of membranes enmeshed within a liquid matrix.
  • This pigment gives plants their characteristic green hue and helps to absorb light energy.
  • Chloroplasts are found in the cells of the mesophyll of leaves.
  • Each mesophyll cell normally has 30 to 40 of them.

Structure of Chloroplasts

  • Chloroplasts in higher plants often have a biconvex or planoconvex shape.
  • However, different plants may have chloroplasts with different morphologies, such as spherical, filamentous, saucer-shaped, discoid, or ovoid.
  • They may be discovered in the mesophyll cells of plant leaves. Their centres are colourless and vesicular.
  • The chloroplast typically measures 4-6 in diameter and 1-3 in thickness.

The chloroplast has an empty intermediate area between its inner and outer membranes. The thick fluid known as stroma and stacks of thylakoids known as grana are both found within the chloroplast. The chlorophyll required for the plant to undergo photosynthesis is present in these thylakoids. The thylakoid space is the area that chlorophyll occupies.

A chloroplast thus has the following parts: 

1. Envelope (outer membrane)

It has a semi-permeable membrane that easily allows ions and tiny molecules through. The outer membrane is impermeable to larger proteins.

2. Intermembrane Space

Between the chloroplast’s outer and inner membranes, there is typically a narrow intermembrane gap of 10–20 nanometers. 

3. Inner membrane

The inner membrane of the chloroplast surrounds the stroma. It regulates the flow of substances into and out of the chloroplast. In addition to controlling activity, the inner chloroplast membrane also makes fatty acids, lipids, and carotenoids.

4. Stroma

The inner membrane of the chloroplast contains stroma, an alkaline, protein-rich aqueous fluid. The stroma is the region outside the thylakoid space. The stroma contains many proteins, starch granules, chloroplast ribosomes, chloroplast DNA, and the thylakoid system.

5. Thylakoid System

The thylakoid system is hanging in the stroma. The thylakoid system is made up of many membrane sacs called thylakoids. Chlorophyll is present in the thylakoids, which serve as the site where the photosynthesis process’ light reactions take place. Grana, or stacks of thylakoids, is how they are organised. Per granum, there are about 10–20 thylakoids.

6. Peripheral Reticulum

A second pair of membrane tubules exists in certain plants termed the peripheral reticulum in their chloroplasts that come from the envelope’s inner membrane. Tiny vesicles that break out from the inner membrane of the chloroplast make up the tubules of the peripheral reticulum.

Functions of Chloroplasts

  • In the process of photosynthesis In chloroplasts, solar energy is captured and converted into chemical energy via a series of light-dependent as well as light-independent chemical reactions.
  • Both photorespiration and other cellular regulatory processes are aided by the chloroplast’s constituent parts.
  • The generation of fatty acids, membrane lipids, isoprenoids, tetrapyrroles, starch, and hormones are only a few of the many metabolic processes carried out by chloroplasts on behalf of plant cells.
  • The plant reaction involves all plant cells, so there are no specialist immune cells in plants.
  • The main organelles of pathogen defence are the chloroplasts, cell membrane, nucleus, and ER.
  • Cellular sensors might be chloroplasts.


  • Verma, P. S., & Agrawal, V. K. (2006). Cell Biology, Genetics, Molecular Biology, Evolution & Ecology (1 ed.). S .Chand and company Ltd.
  • Stephen R. Bolsover, Elizabeth A. Shephard, Hugh A. White, Jeremy S. Hyams (2011). Cell Biology: A short Course (3 ed.).Hoboken,NJ: John Wiley and Sons.
  • Alberts, B. (2004). Essential cell biology. New York, NY: Garland Science Pub.
  • https://biologywise.com/chloroplast-structure-function
  • https://alevelbiology.co.uk/notes/chloroplasts-structure-and-functions/
  • https://study.com/academy/lesson/chloroplast-definition-structure-function-examples.html
  • https://biologydictionary.net/chloroplast/
  • https://www.microscopemaster.com/chloroplasts.html
  • https://www.frontiersin.org/research-topics/5623/structure-and-function-of-chloroplasts
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