i) Plasmodium
ii) Paramecium
iii) Euglena

Acetobacter is a genus of bacteria that oxidize ethanol and produce acetic acid.

i) Rhizobium,
ii) cyanobacteria and
iii) Nostoc.

a) Natural fertilizer:
Micro organisms act upon degradable waste and making the soil fertile.
b) Nitrogen fixation
Rhizobium bacteria living in the root nodules of leguminous plants enrich the soil by fixing the atmospheric nitrogen as nitrates.
c) Bio control agents:
Bacillus thuringiensis control insects trichoderma protects, roots and control plant pathogens. Baculoviruses attack insects and other arthropods.
(OR)
Microorganisms make compost from degradable waste, fix the atmospheric nitrogen.

Disease causing micro organisms are called pathogens.
Pathogenic organisms are of 5 types :
i) viruses
ii) fungi
iii) worms
iv) bacteria
v) protozoa

i) Bacilli - Rod shaped bacteria.
Eg. Bacillus anthracis
ii) Spirilla - Spiral shaped bacteria.
Eg. Helicobacter pylori.
iii) Cocci - Spherical or ball shaped bacteria
Eg. Streptococus pneumoniae
iv) Vibrio - Comma shaped bacteria
Eg. Vibrio cholera

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