Samacheer Class 8 Science - Micro Organisms

Bacteria are described according to the shape of their cells. They are:
Bacilli – Rod shaped bacteria.
Spirilla – Spiral shaped bacteria.
Cocci – Spherical or ball shaped bacteria.
Vibrio – Comma shaped bacteria.

The disease causing microbes are called pathogens. They enter into the body through –
Cuts and wounds in the skin, mouth or nose.
Some pathogens are found in air and enter into a healthy person by breathing. When a patient sneezes, droplets containing microbes spread in air. Example: Tuberculosis, Flu.
Some pathogens enter into our body through food and water contaminated with the pathogen. Example: Cholera.
Pathogens also enter through blood transfusion from a infected to healthy person. Example: Aids

1. Bacteria are single – celled prokaryotes (cells without nuclei).
2. Bacteria are grouped under the kingdom Monera. The study of Bacteria is called Bacteriology.
3. Bacteria are of two types based on respiration
Aerobic bacteria (requires oxygen).
Anaerobjc bacteria (Does not requires oxygen).
4. A bacterium has an outer covering known as the cell wall. Nuclear material is represented by a nucleoid without nuclear membrane.
5. An extra chromosomal DNA called plasmid is present in the cytoplasm.
6. Protein synthesis is carried out by 70S ribosomes. Other cell organelles (mitochondria, Golgi body endoplasmic reticulum etc.,) are absent. Flagella aids in locomotion.
7. Bacteria are described according to the shape of their cells. They are:
Bacilli – Rod shape bacteria
Spirilla – Spiral shaped bacteria
Cocci – Spherical or ball shaped bacteria
Vibrio – Comma shaped bacteria
Bacteria are also classified according to number and arrangement of flagella as follows:
Monotrichous – Single flagella at one end. Example: Vibrio cholera
Lophotrichous – Tuft of flagella at one end. Example: Pseudomonas.
Amphitrichous – Tuft of flagella at both ends. Example:Rhodospirillum rubrum.
Peritrichous – Flagella all around. Example: E.coli.
Atrichous – Without any flagella. Example: Corynebacterium diptherae.

Role of microbes in medicine:
We obtain antibiotics and vaccines from microbes.
1. Antibiotics:
It is a substance produced by living organisms which is toxic to other organisms. The antibiotic penicillin got from the fungus Penicillium chrysogenum is used to treat diseases like tetanus, diphtheria. Streptomycin got from streptomyces bacteria is used to cure bacterial infections like plague.
2. Vaccines:
They are prepared from dead or weakened microbes. When a vaccine is injected into the body of a patient, it produces antibodies to fight the germs. These antibodies protect the body from infections in future. Example: MMR vaccine for measles.

We can improve the beneficial bacterial count in human beings by adopting the following methods:
Intake of fibre rich foods.
Intake of seasonal fruits and vegetables.
Intake of plenty of fermented foods with live microbes. Eat more of prebiotic foods.
Intake of whole grains.
Prefer plant based diet.
Avoid artificial sweeteners.

Probiotics:
Probiotics are live food supplements used in yoghurt and other fermented milk products. Example: Lactobacillus acidophilus and Bifidobacterium bifidum. These bacteria improve the microbial spectrum in the gut and thus contribute to the following effects:
Decrease the risk of colon cancer
Decrease cholesterol absorption
Prevent diarrheal diseases by increasing the immunity power.