1 The World of Microbes Science for grade 8 Chapter - 7

Module Objectives To know about the meaning of microorganisms To know how to record observations made using microscope To develop skill of preparing microscopic slides Compare characteristics of different group of microorganisms Reason out the need to be hygienic

Micro Organisms You find many living and non living things around you. But did you know that there is a world of living beings which cannot be seen through our naked eye???? These organisms are called micro organisms. Bacteria,protozoa,fungi,algae and virus are all micro organisms.

Activity Here is a fun activity for you !! Take a sample of curd. Put a drop of curd on the microscope slide. Dry it and add methylene blue stain to it. Now, observe this under the compound microscope, under oil immersion magnification. What would you observe ? Tiny rod like objects which you see are the micro organisms, which have converted milk into curds. This is a type of bacteria Known as the LACTOBACILLUS. 23/05/2015

Does life beget life ?? Louis Pasteur, the famous scientist proved this by his swan neck flask experiment. He proved that life arises from pre existing life itself. 23/05/2015

Shapes of bacteria Have you ever wondered what the shape of bacteria could be ?? Spherical ? Rod shaped ? Spiral ? Comma shaped ? Well, all these are right. Different bacteria have different shapes like spherical, rod shaped, comma shaped or even spiral ! Spherical ones are called cocci comma shaped ones are called vibrio.Spiral ones are known as spirilli and rod shaped ones are called bacillus. 23/05/2015

Shapes of bacteria Cocci bacteria may be single, in pairs, in clusters and also in chains ! 23/05/2015

Structure of a typical bacterium Cellwal – outer most layer. Plasma membrane – present next to the cell wall. It encloses cytoplasm. Flagella – Help the bacterium to move. Capsule – Layer external to the cell wall. Thicker capsule means more disease causing ability The genetic material of a bacteria is not enclosed by a nuclear membrane. Such organisms are called prokaryotes. Bacteria is an example.

What is a bacteriophage? There is a group of viruses which infect bacteria. These are bacteriophages. Bacteriophage is a virus.

Structure of a bacteriophage Head region in a bacteriophage contains the genetic material. The collar contains protein sheath. In viruses, the genetic material is RNA whereas in bacteriophage, the genetic material is DNA Bacteriophage H.I.V.

Amoeba If you observe a drop of stagnant water under a microscope, this is what you would find!!

Amoeba Amoeba is included under the Kingdom ‘Protista’ and is a protozoan. It has an external membrane called ‘cell membrane’ and a nucleus covered by the nuclear membrane. Amoeba moves with the help of pseudopodia. Contractile vacuole helps in excreting excess water and wastes.

Chlamydomonas Here is another commonly found organism. It belongs to Kingdom plantae.

Aspergillus When a lemon is cut and exposed to air for 2 days, a bushy material is formed on the cut side. It has no Chloroplast. It is a fungus called ‘Aspergillus’. They belong to Kingdon Mycota.

Microorganisms and their uses Microorganisms are used in food industry, leather industry, dairy industry, pharmaceuticals, water treatment plants and even sewage treatment plants. They also act as vital decomposers and thus are useful for agriculture However, not all of them are useful. They tend to spoil food and cause diseases in plants and animals.

Microbes and diseases Micro organisms are beneficial to us in some cases. For eg. To turn milk into curd. However, if we neglect hygiene, then we are prone to microbial infections.

Vaccines Vaccines prevent microbial infections. It contains an agent that resembles a disease- causing micro organism. It is often made from weakened or killed forms of the microbe or its toxins. This stimulates the body’s immune system to recognize the micro organism or its toxins.

Some common human diseases caused by microbes.