Biology Notes 2023 on Classification of Living Organisms

Background of Classification of Living Organisms

The categorization of different organisms into different groups with the purpose to study them is known as classification. The first attempt to classify organisms dates back to the 18^th century when Linnaeus published his book System a Nature and divided all organisms into two kingdoms –Planate and Animalia.  Because of this, Linnaeus is called the ’Father of Taxonomy’.

Various Types of Classification of Living Organisms

There are some organisms like bacteria, viruses, fungi and euglena whose position is disputed and therefore, there is a need of reconsideration of the system of classification.

• Two kingdom classification was given by Carolus Linnaeus, in which he classified organisms into Plantae and Animalia.
• Three kingdom classification was given by Ernest Haeckel i.e. Plantae, Protista and Animalia.
• Four kingdom classification was given by Copeland i.e. Monera, Protista, Plantae and Animalia.
• Five kingdom classification was given by RH Whittaker. This is the most popular and commonly followed classification.
• The latest system of classification is the Six Kingdom System given by C Woose, O Kandler and Mc Wheels.

Also Check: Various Diseases and Associated Part of Human Body Study Notes

Five Kingdom Classification

This was proposed by R. H. Whittaker in 1969 and he divided the organisms into 5 categories viz. Monera, Protista, Fungi, Plantae and Animalia.
These 5 categories are based on various factors like the complexity of cell structure, the complexity of the body of an organism, mode of nutrition, lifestyle and phylogenetic relationship. A brief description of all the categories are as follows:

Monera:  All organisms of this kingdom are microscopic. Prokaryotic organisms like bacteria, cyanobacteria and archaebacteria, mycoplasma, actinomycetes and Rickettsia are covered in this type. It also covers Filamentous bacteria under this kingdom.

Protista: It is placed between plants and animals and includes the unicellular form which is usually found in aquatic habitats. These can be further classified on the basis of nutrition as – autotrophic, parasitic, and saprophytic. Diatoms flagellates and protozoa come under this kingdom. Autotrophic and heterotrophic mode of nutrition is found in Euglena.

Fungi: Mushroom, Mucor, Albugo etc. are some of the examples of this category which is a group of unique organisms having a cell wall of chitin and a heterotrophic mode of nutrition. Mycelium network is found in their body which is filled with filaments called hyphae. 

Plantae: Plants which contain cell walls made up of cellulose are included in Kingdom Plantae. However, some plants are insectivorous and parasites.

Animalia: Almost every animal, which are heterotrophic and multicellular organisms with organs or tissues, comes under this category.

Binomial nomenclature:

This system of nomenclature consists of 2 names, i.e. a generic name and a species name and was proposed by Linnaeus in the book Species Pantarum.
The generic names begin with a special letter and the species name begins with a small letter
Some examples of  the Scientific Names of the organisms under this nomenclature are given below:

 Botany

The scientific study of the physiology, structure, genetics, ecology, distribution, classification and economic importance of plants is called Botany.
Theophrastus is called the father of Botany.
Below given classification of Botany is given by Eichler. The botanical world is mainly classified into two parts (Cryptogams Plants and Phanerogames Plants)

(A) Cryptogamus plants

Flowerless and Seedless plants are classified as Cryptogamus plants. These are further classified into the following groups:

1. Thallophyta

An undifferentiated plant body that has no roots, stems or leaves is called Thallophyta.
This is the largest group in the plant kingdom.
The conducting tissue is not present in these plants

Algae

• Algae are autotrophic, chlorophyll bearing thalloid plants.
• Most of the Algae are aquatic and are classified into three types:
• Red algae are known as Rhdophyceae.
• Green Algae are known as Chlorophyceae
• Brown algae are known as Phaeophyceae
• Reproduction in algae takes by vegetative and sexual means.
• The massive growth of algae is known as the Algal Boom 
• The boom caused by red algae is called Red Tide.

Useful Algae:

Most of the algae are used by humans for various purposes. Some of the examples are: As a food: Porphyra, Ulva, Surgassum, Laeminaria, Nostoc etc.
Iodine Making: Laeminaria and Macrocystis
As Bio fertilisers: Nostoc, Anabina, kelp etc.
Antibiotic: Chlorella for making Chlorellin antibiotic
In Space: Chlorella and Synechococcus are used for the production of Oxygen for Astronauts.

Fungi:
The study of Fungi is called Mycology. Chlorophyll is not present in Fungi Accumulated food in fungi remains as Glycogen. Chitin is the material with fungi cell walls is made up.

2. Bryophyta:

• The peculiar characteristic of this plant division is the presence of mosses, crude stems and leaves and absence of roots.
• Since they are found in dry and moist areas, these plants are commonly known as amphibians of the plant kingdom.
• Xylem and phloem tissue are very less in bryophytes.
• The moss namely Sphagnum is capable of soaking water 18 times its own weight. Therefore, gardeners use it to protect them from drying while taking the plants from one place to another.
• The Sphagnum moss is used as fuel and antiseptic.

3. Pteridophyta

• These are characterized by the lack of flowers like most plants and the presence of ferns.
• Ferns have special stems, called rhizomes, which grow sideways at the surface or underground.
• Spores are responsible for Reproduction produced inside the sporangia.

Examples: Ferns, Azolla, Pteridium, Lycopodium etc

(B) Phanerogamus or Floral plant

All the plants in the Group are well developed and have flowers, fruits and seeds. These are further classified into 2 groups – Gymnosperm and Angiosperm.

1. Gymnosperm

• Typical characteristics of this type are
  • Presence of naked ovules.
  • Plants are woody, perennial and tall.
  • The roots are well developed.
• Pollination takes place through the air.
• Cycas, Ginkgo, biloba and Metasequoia are used as living fossils.
• Ginkgo biloba is also called Maiden hair tree.
• Ovules and Antherzoids of Cycas is the largest in the Plant Kingdom.
• A shower of yellow pollen often seen in spring that is carried by the wind from Pines (such as conifers) is called as Sulphur Showers
• They include the medium-size tree giant redwood tree Sequoia of California (the longest tree of the plant kingdom)
• The smallest plant is Zaimia Pygmia.

2. Angiosperm

Flowers and fruits are the most important feature of this group.

Angiosperms are divided into dicots and monocots based on the presence of 

Dicots have two while monocots have one 

This group include plant ranges from microscopic Wolfia to tall tree. 

Hope this was useful to you.

Happy Learning