Plastid: Different Types of Plastid, Structure and Function of Chloroplast, Chromoplast and Leucoplast

Table of Contents:

1. Introduction

  •  Definition of Plastid

2. Types of Plastids

   a. Chloroplast

  •  Structure of Chloroplast  
  • The Photosynthetic Powerhouse
  • Chloroplast Characteristics
  • Chlorophyll and Its Role
  • Structure of Chloroplast 
  •      - Envelope
  •      - Stroma
  •      - Thylakoids
  • Formation of Grana  
  • Inter-granum

4. Chromoplasts: Adding Color to Plants

  • Role of Chromoplasts
  • Distribution in Plants
  • Contribution to Pollination and Seed Dispersal

5. Leucoplasts: Colorless Storage Units

  • Characteristics of Leucoplasts
  •  Shapes and Locations
  •  Function in Food Storage

6. Comparative Analysis of Plastids

  • Contrasting Features of Chloroplasts, Chromoplasts, and Leucoplasts

Plastid: Different Types of Plastid, Structure and Function of Chloroplast, Chromoplast and Leucoplast



Plastid are membrane bonded mostly pigment containing bodies present in the cell. Plastid are the unique organelles found only in plants. Plastids are three main types. 

  1. Chloroplast:

Plastid: Different Types of Plastid, Structure and Function of Chloroplast, Chromoplast and Leucoplast

In photosynthetic plants cells, these are membrane bounded structure containing a green pigments, chlorophyll. Chlorophyll is an organic compound Chloroplast vary in their shape and size with a diameter of about 4-6 micro meter under electronic microscope they appear to be hetrigenous structure with small granules known as grana embedded in the matrix.

Structure of chloroplast:

Chloroplast consist of three component, 

  1. Envelope
  2. Stroma 
  3. Thylakoide


The envelope is formed formed  by a double membrane, while stroma covers most of the volume of the chloroplast. Stroma is fluid which surrounded the thylakoids. It contains protein, some ribosomes and a small circular DNA. It is in this part of the chloroplast where carbon dioxide is fixed to manufacture sagurs. 


Thylakoids are the flattened vesicles which arrange themselves to form grana. A granum appears to be a pile lf thylakoids stacked on each other like coins. On average there are 50 or more thylakoids piled to formed one granum. On the layers of the thylakoids, chlorophyll molecules are arrange and that’s is why granum appears to be green. Each granum is inter connected with other by the non green part  called inter granum. Chloroplast are also self replicating organelles like mitochondria. 


The stroma is a crucial component of chloroplasts, playing a significant role in the process of photosynthesis within plant cells.

1. Definition:

 The stroma is the semi-fluid matrix or space surrounding the thylakoid membranes inside a chloroplast.

2. Composition:

It consists of a gel-like substance containing enzymes, sugars, ions, and other molecules necessary for the synthesis of organic molecules during photosynthesis.

3. Function:

The stroma is the site for the Calvin cycle, which is the second stage of photosynthesis. In this cycle, carbon dioxide is converted into sugars with the help of enzymes and energy carriers like ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate), which are produced in the thylakoid membranes during the light-dependent reactions.

4. Calvin CycleWithin the stroma, the Calvin cycle involves a series of chemical reactions that ultimately lead to the production of glucose and other carbohydrates. This cycle is crucial for the conversion of carbon dioxide from the atmosphere into organic molecules that the plant can use for energy and growth.

5. Enzymes and Protein Synthesis: Enzymes present in the stroma facilitate various biochemical reactions, including the synthesis of carbohydrates. Additionally, the stroma is involved in the synthesis of some proteins using the information encoded in the plant's DNA.

6. Storage: The stroma also serves as a reservoir for starch granules, which are formed as a result of the glucose produced during photosynthesis. Starch acts as a storage form of energy for the plant.

In summary, the stroma of chloroplasts is a dynamic and essential part of the photosynthetic process. It provides a microenvironment where key biochemical reactions take place, leading to the synthesis of sugars and other organic molecules that support the plant's growth and metabolism.

Plastid: Different Types of Plastid, Structure and Function of Chloroplast, Chromoplast and Leucoplast


Chromoplasts impart colour to the plant parts other then green. Thy are present in the petals of the flowers and in the ripened fruits. They help in pollination and dispersal of seeds.


Leucoplasts are colorless. They are triangular, tabular or of some other shape. They are mostly found in the underground parts of the plants and store food.

Contrasting Features of Chloroplasts, Chromoplasts, and Leucoplasts

Certainly! Here are the contrasting features of Chloroplasts, Chromoplasts, and Leucoplasts.

1. Function:

Chloroplasts: Mainly involved in photosynthesis, containing chlorophyll for capturing light energy.

Chromoplasts: Responsible for storing pigments, contributing to the coloration of fruits and flowers.

Leucoplasts: Primarily for storage of nutrients, such as starch, lipids, or proteins.

2. Color:

Chloroplasts: Green due to the presence of chlorophyll.
Chromoplasts: Various colors depending on the pigments stored, including red, orange, and yellow.

 Leucoplasts: Generally colorless.

3. Pigments:

Chloroplasts: Contain chlorophyll pigments, essential for photosynthesis.
Chromoplasts: Store various pigments like carotenoids, xanthophylls, and anthocyanins.
Leucoplasts: Largely lack pigments but may store other compounds.

4. Location:

 Chloroplasts: Found in the cells of green plant tissues, especially in leaves.

 Chromoplasts: Typically present in colored parts of plants like fruits, flowers, and some roots.

 Leucoplasts: Distributed throughout the plant, often in non-photosynthetic tissues like roots and seeds.

5. Associated Structures:

Chloroplasts: Have thylakoids and grana for the process of photosynthesis.
Chromoplasts: Lack well-defined structures for photosynthesis but may have plastoglobuli.
Leucoplasts: May have different types, including amyloplasts (starch storage), elaioplasts (lipid storage), and proteinoplasts (protein storage).

6. Role in Plant Growth:

   - Chloroplasts: Essential for the plant's energy production and growth.
   - Chromoplasts: Contribute to the attraction of pollinators and seed dispersers.
   - Leucoplasts: Serve as storage organelles, providing reserves for the plant's metabolic needs.
These differences highlight the diverse functions of these plastids in plant cells.

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