Biological Classification

(a) Heterotrophic bacteria: those bacteria that cannot synthesize their own food and rely on their environment for the food source.

(1) Lactobacillus helps in the production of curd from milk.

(2) They aid in nitrogen fixation. Eg Rhizobium and Azotobacter.

(3) They're used for production of antibiotics. (streptomyces griseus is used to make streptomycin)

(b) Archaebacteria: Archaebacteria are a group of microorganisms considered to be a primitive form of life that evolved separately from the bacteria and blue-green algae.

(1) Methane gas is produced from the dung of ruminants by the methanogens.

(2) Methanogens are also involved in the formation of biogas and sewage treatment.

• Diatoms are a major group of algae found in oceans and other water bodies.
• They are unicellular.
• Diatoms are responsible for the production of 20 percent of the Earth's oxygen supply.
• Their call wall is made up of silica and is called frustule.
• It is composed of two overlapping sections called thecae.
• The cell wall consists of cellulose impregnated with silica which show sculpturing and ornamentation.
• Diatoms are often called the pearls of the ocean (or jewels of the sea) because they are often beautifully marked and striated and on interaction with light look like jewels.

Algal bloom refers to the overgrowth and accumulation of algae population in freshwater and marine water bodies.
Not all algal blooms are harmful. The harmful algal blooms are known as HAB (Harmful algal blooms)
There are two major causes of algal blooms: high temperatures and nutrients runoff. (Fertilizers sprayed on crop get washed into the water bodies)

Red tides
Red tides are caused by excessive growth of harmful algal blooms.
These HABs are usually composed of red Dinoflagellates (Eg: Gonyaulax)
Provided optimum conditions, these red Dinoflagellates undergo rapid multiplication.
Due to this overgrowth, the watersurface appears red in colour. Hence, the name red tides.

• Protozoans are unicellular, microscopic eukaryotes.
• All protozoans are heterotrophic.
• Some are free living, others infect higher animals and function as parasites.
• They reproducesmainly through binary fission however exceptions exist.
• They have a holozoic mode of nutrition. (Holozoic means food from the outside has to be ingested and internally broken down for the body to be able to utilise it.)
  
  
  There are four major groups of protozoans:

• Amoeboid protozoans: (example: Amoeba)
  They can be found in fresh water, moist soil and sea water.
  They move with the help of psuedopodia.
  They do not have a periplast (a type of membrane)
  They maybe free living or parasitic.

• Ciliated protozoans: (example: Paramecium)
  They are aquatic.
  Their bodies are covered by tiny hair like structures called cilia.
  They use their cilia for movement and for caputuring their prey.
  They have an outer cavity on their cell surface.
  

• Flagellated protozoans: (example: Trypanosoma)
  These protozoans are either free living or parasitic
  They possess a flagellum.
  They use the flagellum for locomotion.
  

• Sporozoans: (Example: Plasmodium)
  These protozoans have an infective spore-like stage.
  All of them are parasitic
  They have an elaborate life cycle involving more than one host.
  They do not possess any cilia or flagella.

• Some organisms such as lichens have symbiotic relations or associations.
• Symbiosis means that they form a type of a close and long-term biological interaction between two different biological organisms.
• In case of lichens, the two biological organisms in association are: algae and fungi.
• The algal part is known as phycobiont. (autotrophic)
• The fungal part is knwon as mycobiont. (heterotrophic)

• Euglenoids are a group of flagellates.
• They are unicellular and belong to the kingdom Protista.
• They are found in freshwater.
• They have an eyespot
• Instead of a cell wall, they have pellicle which is a protein rich membrane.
• The anterior end of their body has two flagella; one long and one short.
• They are autotrophs as well as heterotrophs.
• When sunlight is present, they can make their own food (because they contain chlorophyll)
• When sunlight is absent, they behave as heterotrophs and consumes smallers organisms.
• They serve as a connecting link between planst and animals.
• Euglena is a euglenoid.

• Viruses are non cellular, obligate parasites. This means that viruses needs a host to survive; they cannot survive on their own.
• Viruses have an outer protein covering known as capsid and their own genetic material which can be RNA or DNA.
• They never contain both DNA and RNA.
• Their genetic material is what causes viral infections.
• Viruses can have different shapes such as helical, icosahedral, complex etc.

• Viruses cause diseases like mumps, small pox, herpes and influenza.
• AIDS in humans is also caused by a virus.
• In plants, discoloration and mottling (formation og irregular patterns) is caused by the TMV (Tumor Mosaic Virus)