(i) What are the various types of plastids?
(ii) Describe the chemical composition and functions of eukaryotic cell wall.
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(i)1. Plastids are classified according to the pigments present in it. Three main types of plastids are – leucoplasts, chromoplasts and chloroplasts.
2. Leucoplasts do not contain any photosynthetic pigments they are of various shapes and sizes.
These are meant for storage of nutrients:
a. Amyloplasts store starch.
b. Elaioplasts store oils.
c. Aleuroplasts store proteins.
3. Chromoplasts contain pigments like carotene and xanthophyll etc.
a. They impart yellow, orange or red colour to flowers and fruits.
b. These plastids are found in the coloured parts of flowers and fruits.
4. Chloroplasts are plastids containing green pigment chlorophyll along with other enzymes that help in production of sugar by photosynthesis. They are present in plants, algae and few protists like Euglena.
(ii)1. The rigid, protective and supportive covering, outside the cell membrane is called cell wall. It is present in plant cells, fungi and some protists.
2. Algae show presence of cellulose, galactans, mannans and minerals like calcium carbonate in cell wall.
3. In other plants, it is made up of hemicelluloses, pectin, lipids and protein.
4. Microfibrils of plant cell wall show presence of cellulose which is responsible for rigidity.
5. Some of the depositions of cell wall are silica (grass stem), cutin (epidermal walls of land plants), suberin (endodermal cells of root), wax, lignin.
6. Function:
Provides support, rigidity and shape to the cell.
Protects the protoplasm against mechanical injury and infections.
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