One shot / Class 11th Biological classification

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Biological Classification – Important Points, Summary, Revision, Highlights
Biological Classification
The process of grouping together various organisms according to their similarities, dissimilarities and phylogenetic descent is known as biological classification.

There have been various attempts to classify organisms. The earliest was by Aristotle, who classified plants into herbs shrubs and trees. He classified animals into two groups, based on the presence and absence of red blood.
Linnaeus gave the Two Kingdom system of classification and divided living organisms into Plantae and Animalia.

R.H. Whittaker proposed the Five Kingdom system of classification and classified organisms, based on cellular structure, complexity, mode of nutrition, phylogenetic relationship and ecological role performed by them.

Whittaker divided organisms into Monera, Protista, Fungi, Plantae and Animalia
1. Monera
This group includes all kinds of bacteria, having a prokaryotic cell.
The cell does not contain a well-defined nucleus.
There are different shapes of bacteria present; spherical- cocci, rod-shaped- bacillus, comma- vibrio and spiral- spirilla.
They mainly reproduce by fission, spore formation under unfavourable conditions and also by DNA transfer from one bacterium cell to another.
Mycoplasma lack the cell wall and are the smallest cell to survive
Archaebacteria- These bacteria are present in the harshest environmental conditions, such as salty, marshy and in hot springs. They are known as halophiles, methanogens, and thermoacidophiles, respectively.
Methanogens are present in the gut of ruminants and produce biogas.
Eubacteria- These are true bacteria and have a rigid cell wall, and motile organisms have flagella.
Photosynthetic Autotrophs- They include Cyanobacteria (Blue-green Algae). They have chlorophylls and carotenoids. They are unicellular, filamentous or colonial and body is covered by a mucilaginous sheath. Nostoc and Anabaena have heterocysts, where they can fix atmospheric nitrogen.
Chemosynthetic Autotrophs- They play an important role in recycling nutrients. They get the required energy for ATP generation from the oxidation of various inorganic substances such as ammonia, nitrates and nitrites.
Heterotrophic- There is a wide variety of heterotrophic bacteria. They act as a decomposer. They are used for various purposes such as nitrogen-fixing, curd and antibiotics production. Many bacteria are pathogen causing various diseases of plants and animals, e.g. citrus canker, tetanus, typhoid, cholera.
2. Protista
The group includes unicellular eukaryotes
A photosynthetic protist is a link between plants and animals
They contain a well-defined nucleus and other membrane-bound cell organelles
They include protozoan, slime moulds, chrysophytes, dinoflagellates and euglenoids
2.1 Chrysophytes

Include diatoms and desmids (golden algae)
They are mostly photosynthetic and have indestructible cell wall due to the presence of silica
The cell wall makes two thin overlapping shells, which fit like a soapbox on the outer surface
Diatomaceous earth is the deposit of the cell wall that gets accumulated. It is used for filtration and polishing
2.2 Dinoflagellates

They are photosynthetic and marine
They are found in many colours like yellow, green, red, blue, brown, according to the pigment present
Stiff cellulose plates are present on the cell wall
They multiply rapidly and cause red tide
Many dinoflagellates emit blue-green light and are bioluminescent
2.3 Euglenoids

They are photosynthetic flagellated protist
They are a link between plants and animals. They perform photosynthesis but lack a cell wall
The characteristic feature is the presence of pellicle, a protein-rich layer, which makes their body flexible
In the absence of sunlight, they feed on small organisms and behave as a heterotroph

2.4 Slime moulds

They are saprophytic protists feeding on organic materials from decaying twigs and leaves
Aggregation of slime moulds is called plasmodium, which they form under favourable conditions
Under unfavourable conditions, fruiting bodies containing spores develop at the tip of plasmodium
These spores can survive for very long under adverse conditions and have true walls
2.5 Protozoans

The group contains all the unicellular, eukaryotic, heterotrophs, which are parasites or predators
These are divided into 4 major groups:
Amoeboid- They are characterised by the presence of pseudopodia, which are used for movement and catching of prey, e.g. Amoeba. Marine amoeboids have silica shells. Some of the amoeboids are parasites, e.g. Entamoeba histolytica causes amoebic dysentery
Flagellated- They are characterised by the presence of flagella. Some of them are parasites causing various diseases, e.g Trypanosoma causes sleeping sickness
Ciliated- Note- Further notes are given in video thankyou
by Ishu sir