Plastids are the largest cell organelles bounded by double membrane. These are found in most of the plants cells. These are absent in prokaryotes and animal cells. It’s of three types.1.Chloroplasts 2.Chromoplasts and 3.Leucoplasts.
Plastids are huge cytoplasmic organelles. Plastids are major organelles and are found in the cell of plants and in algae. Plastids are site of the manufacture and storage of important chemical compounds that are used by the cell. Plastids often contains pigments that is used in photosynthesis, and the type of pigments present can change or determine the cell’s color. The term plastid was derived from a Greek word “plastikas” means formed or moulded. This term was given by Schimper in 1885.
Chromoplasts are colored plastids. In this chromo means “color” and plastid refers to “living”. Chromoplasts contains various pigments. They uses the photosynthesis process to synthesize the food materials. They contains red, orange or red pigments. Chloroplasts are commonly found in fruits and flowers. Chromoplasts are further divided into three types based on their color namely phaeoplast, chloroplast and rhodoplast
Chloroplast can be discussed separately because of it’s significance.
Chromoplasts: These are colour ones other than green.These can be found in various coloured parts namely petals of flower ,pericarp of fruit etc.
Leucoplast: These are the colourless ones involved in the storage of carbohydrates,fats and oils and proteins. Those ones which stores carbohydrates called as amyloplasts while plastids storing fats and oils are called elaioplasts whereas protein storing plastids are called proteinoplasts.
In plants, plastids can be differentiated into several forms, and it further depends that which function they need to play in the cell.
Mainly there are two major categories namely leucoplasts and chromoplasts.
Leucoplasts are non-pigmented plastids. As it name suggests, Leuco means white and plast means living. They mains work to store food materials. They are generally not involved in synthetic activities. These leucoplasts are further sub-divided into three types namely amyloplast, elasioplast and proteinoplast.
Amyloplast : It stores starch and is found in cotyledons, tubers and endosperm.
Elaioplast : It mainly stores oil found in epidermal cells.
Proteinoplast: This is found in seeds and nuts and stores proteins.
Chromoplast : These are colored plastids, as the name suggests chromo means color and plast means living. Chromoplast contains various pigments. These synthesizes food material by photosynthesis. They contains orange, yellow and red pigments. Chromoplasts are found generally in fruits and flowers. Chromoplasts are further divided into three types based on the color namely phaeoplast, chloroplast and rhodoplast.
Phaeoplast: Its color is dark brown. It contains pigments named fucoxanthin. It is found in brown algae, dinoflagelates and diatoms.
Chloroplast: Its color is green. It contains chlorophyll pigments. It is found in green algae and higher plants.
Rhodoplast: Its color is red. It contains phycoerythrin. It is generally found in red algae.
Chloroplasts are organelles found in eukaryotic organisms that conduct photosynthesis and in plants. The word chloroplasts is taken from Greek words “chloros” which means green and “plast” which means entity or form. Chloroplasts are members of a class of organelles called as plastids.
Shape : Chloroplasts greatly varies in their shape. They are of ovoid, spheroid or discoid shape in higher plants. They are also cup-shaped in chlamydomonas and spirally coiled in the spirogyra.
Size : The size of plastids varies between species to species. But this size remains constant for a given particular cell type. In higher plants, it can be 4-5 microns in length and about 1-3 microns in thickness.. Generally chloroplasts of those plants which grow in shady places are larger in size.
Number : Number of chloroplasts also varies from plants to plants, but it remains constant for any given particular plant. In some higher plants, there are about 20 to 40 chloroplasts per cell upto 1000 chloroplasts.