CBSE Class 9 Answered

Diatoms are a major group of eukaryotic algae, and are one of the most common types of phytoplankton. Most diatoms are unicellular, although they can exist as colonies. Diatoms occur in both marine and fresh water.

Diatoms are producers within the food chain.

Diatom communities are a popular tool for monitoring environmental conditions, past and present, and are commonly used in studies of water quality. .

The cell walls of these organisms are made of silica, and the varied shapes and beautiful ornamentation of these walls made the study of the diatoms a favored pursuit of the microscopical pioneers. The cell wall is also one of the major reasons why these algae are studied extensively for ecological and evolutionary researches, because the fossils are often well preserved in lake and marine systems.

Agar or agar agar is a gelatinous substance derived from seaweed. is an unbranched polysaccharide obtained from the cell walls of some species of red algae, primarily from the genera Gelidium and Gracilaria, or seaweed (Sphaerococcus euchema). Commercially it is derived primarily from Gelidium amansii.

It is used mainly in microbiological experiments as a culture medium for growing bacteria and other micro-organisms. The agar is resistant to breakdown by micro-organisms, remaining a solid jelly throughout the course of the experiment.

It is chiefly used as an ingredient in several desserts.

In addition, agar agar can be used for severalpurposes such as a laxative, a vegetarian gelatin substitute, a thickener for soups, in jellies, ice cream, a clarifying agent in brewing, in preserved foods and for paper sizing fabrics.