BIOLOGY FOR CLASS IX

 Content  Micro-organisms, a heterogenous group of living organisms which can only be seen with the help of microscope.  Discovery of virus, characteristics, structure, types and the diseases caused by viruses in humans, other animals and plants.  Characters of bacteria.  Shapes, nutrition and importance of bacteria.  Characters of cyanobacteria. Viruses, Bacteria and Cyanobacteria Class IX

Microorganisms are often illustrated using single-celled, or unicellular organisms However and some multicellular species are microscopic.e.g. bacteria, fungi, viruses.

A virus is a small infectious agent that replicates only inside the living cells of other organisms. Viruses can infect all types of life forms, from animals and plants to microorganisms, including bacteria.

They are enclosed in a protective envelope. They have spikes, which helps them to attach to the host cell. They do not respire, do not metabolize and do not grow but they do reproduce. They contain a protein coat called the capsid. They have a nucleic acid core containing DNA or RNA. Ribosomes and enzymes are absent, which are needed for metabolism. They are considered both as living and non living things, as viruses are inactive when they are present outside of host cells and are active in side of host cells. As they make use of raw materials and enzymes of the host cell to reproduce and causes several infections. Characteristics :

Virus has a covering that has a capsid and sometimes an envelope Inner core contains a nucleic acid molecule (DNA or RNA) and various proteins Viruses are usually very specific to their host and to the cells they can infect

1. Animal diseases Cold are viral infection. Polio Measles and mumps. Human Immune Virus Deficiency syndrom(Aids) Control By MMR (Measles, Mumps, and Rubella) vaccination. 2. Plant diseases Tobacco Mosaic Virus

Barley Yellow Dwarf Cucumber Mosaic Virus, tomato, peppers, melons, squash, spinach, celery, beet and other plants. The virus causes twisting in young leaves. Sugarcane Mosaic Virus 2.Plant diseases Tobacco Mosaic Virus

Bacteria are tiny single-cell microorganisms, usually a few micrometers in length that normally exist together in millions. Coccus (spherical) They are spherical and according to cell-arrangement they are: Solitary (single) Monococcus), in pair (Diplococci), in chain (Streptococci), in cluster (Staphylococci) etc.They are non-flagellated. Bacillus(rod-like) They are rod shaped. They may be found in pairs (Diplobacillus) or in chains (Streptobacillus) etc. They may be flagellated.

Spiral Spirilla: They are spiral or cork screw shaped (spirillum). According to their mode of feeding, heterotrophic bacteria may be saprophytic, symbiotic or parasitic. Saprophytic Bacteria The soil is full of organic compounds in the form of humus. Bacteria living in the soil have large number of enzymes that break down the complex substances of humus to simpler compounds. These bacteria absorb and utilize these simple compounds as a source of energy

Symbiotic bacteria: Nitrogen-fixing bacteria are microorganisms present in the soil or in plant roots that change nitrogen gases from the atmosphere into solid nitrogen compounds that plants can use in the soil.

Parasitic bacteria: They grow inside the tissues of other living organisms and obtain food at the expense of host. These bacteria lack certain complex systems of enzymes. Typhoid fever bacteria

1.Agricultural bacteria 2.Alimentary canal bacteria 3.Industrial bacteria 4.Medicinal bacteria: Valuable antibiotic drugs have been obtained from bacteria, e.g Thyrothycin,