Antoni Van Leeuwen Hoek, a Dutch lens maker was the first to observe some tiny organisms in a drop of water with the help of a simple microscope.

Blue-green algae have a blue pigment, i.e. cyanin along with chlorophyll. Thus, they are called cyanobacteria.

The rod-shaped bacteria are called bacilli, round shaped are called cocci, spiral shaped are called spirilla, and comma-shaped are called vibrious. 

The organisms that live in a host's body and benefit from it, without harming or helping the host are called commensals.

Red algae yields algin, a gummy substance used to thicken cosmetics and food items like ice cream, jelly and chocolate. 

Some bacteria survive adverse conditions by forming a spore or a cyst (a protective coating). When the environment improves, they come to life again, and begin multiplying.   

Spirogyra is green algae, which is made of a large number of cylindrical cells, which join together in a chain to form a filament. 

Chlamydomonas is a green alga. The top of the cell bears two flagella, used for swimming. 

In spirogyra, the chloroplasts are ribbon-shaped and are arranged in a spiral band. 

Chlorella contains lots of proteins, fats, vitamins and minerals. For this reason, it is cultivated widely to use as a food supplemented. 

Bacteria are unicellular and prokaryotic organisms. 

Volvox is a green, freshwater alga, which lives in colonies in ponds or pools of water. 

Euglena is an autotropic protozoa, which perform photosynthesis. 

Euglena is an autotropic protozoa, which does not harm the environment. 

Paramoecium swims by beating its cilia against the water. 

There are various forms of Englena. Some are parasitic and some are saprophytic. Certain species are autotrophic. 

Amoeba ingests food, digests it inside the body and excretes the waste out of the body. Thus, it has holozoic mode of nutrition.

The study of fungi is called mycology. 

Lichens are symbionts as they live in symbiotic relationship with cyanobacteria.

Rhizopus and mucor are called bread moulds as they grow easily on bread.

Agaricus bisporus is cultivated in more than 70 countries and is one of the most commonly and widely consumed mushrooms in the world. 

A mass of hyphae is called mycelium. A hypha is an elongated cell with many nuclei and branches.

Viruses are acellular. This means that their body has no cellular substance or nucleus. 

Virus, which attack bacteria, are called bacteriophages. 

The milk is fermented by lactobacillus, a bacterium present in curd. 

Salmonella and escherichia coli, cause gastro enteritis. 

Influenza is a viral disease. 

Dysentery is caused by a protozoa - Giardia. It is not a viral disease.

Late blight of potato is a fungal disease. 

Diatoms are highly absorbent and fire resistant and are used for the insulation of pipes, refrigerators and furnances. 

Athlete's foot and dhobi's itch are examples of fungal skin infections.