PLASTID

PLASTID

Nature and Occurrence

• Occur in most plant cells and are absent in animal cells.
• They have their own genome (DNA) and ribosomes.
• They are self-replicating organelles i.e. they have power to divide.
• Fungi (plants) lack plastids.

Types of Plastids

Plastids are of three types :

• Chromoplasts : Coloured plastids (i.e. orange, yellow, green etc.) present in leaves, flowers and fruits.
• Chloroplasts : Plastids having green pigment chlorophyll, are called chloroplasts. Hence, they take part in photosynthesis. Therefore, it is called ‘kitchen of the cells'
• Leucoplast: They are colourless plastids and are mostly found in storage organs e.g. potato and nuts.

Plastid is bound by two unit membranes. It shows two distinct regions.

• Grana : They are the main functional units of chloroplast and are the site of light reaction during photosynthesis
• Stroma : It is a homogeneous matrix in which grana are embedded. Stroma contains variety of photosynthetic enzymes, starch grains, DNA and ribosomes and are the site of dark reaction during photosynthesis.

The types of plastids are summarized below:-

The plastids can be changed from one type to other if the need arise

Functions

Plastids perform following functions :

• Chloroplasts trap solar energy and utilize it to manufacture food for the plant.
• Chromoplasts impart various colours to flower to attract insects for pollination .
• Leucoplasts store starch, fats and protein granules in storage organs.

Internal Structure of Chloroplast

Related Topics

• Peroxisomes
• Cytoplasm
• Nucleus