Important Topic Of Biology: Plastid 

Definition:

Plastids are double membrane-bound organelles found in living organisms like algae, plants and in some eukaryotic organisms. They are responsible for preparing the food and storing them. They have pigments that are helpful in the process of photosynthesis. They are known as intracellular endosymbiotic cyanobacteria.

The word plastid comes from the Greek word plastos which means formed or molded. Schimper was the first scientist who named plastids and gave a clear definition of them. The plastids were first discovered by Haeckel scientists.

They are the sites for manufacturing and storing some important chemicals which are used by autotrophic eukaryotic cells. The type of pigment which is in the cell determines the color of the cell. The genetic material present in them is a circular double-stranded DNA molecule. Plastid is one of the cell organelles because it takes part in energy transduction in cells. The scientist Schimper named plastids those which participate in photosynthesis. Chloroplast is one of the examples of plastid which is responsible for capturing, converting, and conserving solar energy in the form of chemical energy. Plastids are further classified into color or colorless types which are present all over the plant body.

 

Types of plastids:

In plants, plastids can store starch and can synthesize fatty acids which further produce energy and materials for synthesizing the other molecules. All Plastids are derived from proplastids which are located in a meristematic region in plants. Proplastids are divided by binary fusion.

They are further divided into many forms depending on the function they perform and also based on the presence and absence of pigments in them.

They are:

Chloroplasts: Chloroplasts are double-membrane semi-porous in structure. They are in biconvex shape and are found in the mesophyll of the plant cell. They take part in synthesizing food by the process of photosynthesis.

Chromoplasts: In chromoplasts, all pigments are kept and synthesized. They are mainly found in flowering plants, maturing leaves, and fruits. Chloroplasts are converted into chromoplasts. These are having carotenoid pigment which gives a different colour to leaves and fruits in plants. The importance of this pigment is to attract pollinators which are crucial in the pollination process for cross-pollination.

Gerontoplasts: These are aging chloroplasts. Gernoplasts are chloroplasts of the leaves which help to convert into different organelles. When the leaf is no longer using photosynthesis mainly in the autumn month.

Leucoplasts: These are non-pigmented organelles or also known as colorless plastids in the plant body. Leucoplasts are mostly found in non-photosynthetic parts of the plant like roots. Their function is storing starch, lipids, and proteins depending on the need of the plant. They are mostly used for converting amino acids and fatty acids. They are further divided into three types:

• Amyloplasts: these are the greatest in leucoplasts and they store, synthesize the starch.
• Proteinoplasts: they help in storing proteins when a plant needs them and are typically found in seeds.
• Elaioplasts: these leucoplasts type stores fats and oils when needed by plants.

Types in Algae and Protista:

• Chloroplast:- They are mainly found in green algae and other organisms.
• Muroplasts:- These are also known as cyanoplasts or cyanelles and these have a peptidoglycan cell wall which is similar to prokaryotes.
• Rhodoplasts:- These are found in red algae, and hence they are known as red plastids which help to photosynthesize to a depth. These differ from chloroplast in their ability to synthesize starch. In red algae, floridean starch is synthesized and stored outside the plastids in cystols.
• Leucoplast:- Unpigmented plastids. Functions are different from plant leucoplasts.
• Apicoplast:- Non-photosynthetic plastid of apicomplexa derived from endosymbiosis.

Structure of plastids:

Plastids are double membrane-bound organelles which means it has two cell membranes around them. The two membranes are 7nm thick and the space between the two membranes is known as periplasmic space. During the period between proplastic becoming mature plastid inner membrane folds in which is crucial. Chloroplast, which is a type of plastid, is completely filled with stroma (the liquid part) in which highly organized structures known as grana are found. Stromic fluid contains grana, enzymes, circular double-stranded DNA, RNA, and 70s ribosomes.

Importance of this chapter in NEET:

This chapter is more important as it is about the basic unit of structure and its responsibility for many functions. It’s compulsory to know about the structure of living organisms that are living with us in this environment. As these are basic chapters for the subject the examiner doesn’t skip questions related to this area. They may ask about plastids or their genetic material, positions, functions, or their types in plants, algae, and Protista. They can ask singly about their type of plastid like colorless plastid?. So you may get two to five bits from this area which you can get easily when you refer to this article. So, don’t avoid this area thinking it’s easy. It’s easy but needs attention.

Also read: Important Topic Of Biology: Cell Cycle

FAQs:

What do you mean by plastids?

Plastids are double membrane-bound organelles found in living organisms like algae, plants, and in some eukaryotic organisms. They are responsible for preparing the food and storing them. They have pigments that are helpful in the process of photosynthesis. They are known as intracellular endosymbiotic cyanobacteria. The word plastid comes from the Greek word plastos which means formed or molded. Schimper was the first scientist who named plastids and gave a clear definition of them. The plastids were first discovered by Haeckel scientists. They are the sites for manufacturing and storing some important chemicals which are used by autotrophic eukaryotic cells. The type of pigment which is in the cell determines the color of the cell.

Q. Write about types of plastids in plants?

Ans: In plants, plastids can store starch and can synthesize fatty acids which further produce energy and materials for synthesizing the other molecules. All Plastids are derived from proplastids which are located in a meristematic region in plants. Proplastids are divided by binary fusion.

They are further divided into many forms depending on the function they perform and also based on the presence and absence of pigments in them.

They are:

Chloroplasts: Chloroplasts are double-membrane semi-porous in structure. They are in biconvex shape and are found in the mesophyll of the plant cell. They take part in synthesizing food by the process of photosynthesis.

Chromoplasts: In chromoplasts, all pigments are kept and synthesized. They are mainly found in flowering plants, maturing leaves, and fruits. Chloroplasts are converted into chromoplasts. These are having carotenoid pigment which gives a different colour to leaves and fruits in plants. The importance of this pigment is to attract pollinators which are crucial in the pollination process for cross-pollination.

Gerontoplasts: These are aging chloroplasts. Gernoplasts are chloroplasts of the leaves which help to convert into different organelles. When the leaf is no longer using photosynthesis mainly in the autumn months.

Leucoplasts: These are non-pigmented organelles or also known as colorless plastids in the plant body. Leucoplasts are mostly found in nonphotosynthetic parts of the plant like roots. Their function is storing starch, lipids, and proteins depending on the need of the plant. They are mostly used for converting amino acids and fatty acids. They are further divided into three types:

• Amyloplasts: these are the greatest in leucoplasts and they store, synthesize the starch.
• Proteinoplasts: they help in storing proteins when a plant needs them and are typically found in seeds.
• Elaioplasts: these leucoplasts type stores fats and oils when needed by plants.

Q. What type of plastids are present in algae and protists?

Ans: Types of plastids present in algae and protista are:

• Chloroplast:- They are mainly found in green algae and other organisms.
• Muroplasts:- These are also known as cyanoplasts or cyanelles and these have a peptidoglycan cell wall which is similar to prokaryotes.
• Rhodoplasts:- These are found in red algae, and hence they are known as red plastids which help to photosynthesize to a depth. These differ from chloroplast in their ability to synthesize starch. In red algae, floridean starch is synthesized and stored outside the plastids in cystols.
• Leucoplast:- Unpigmented plastids. Functions are different from plant leucoplasts.
• Apicoplast:- Non-photosynthetic plastid of apicomplexa derived from endosymbiosis.