Classification Of Living Things

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In today’s class, we will be talking about the classification of living things. Enjoy the class!

Classification of Living Things

Modern classification of living organisms

Classification of living things is the sorting or grouping of living things; according to their common or similar characteristics. The scientist who developed the first system of classification is called Carolus Linnaeus. All organisms cannot be classified as either plants or animals based on Carolus Linnaeus classification. Therefore five kingdoms have been generally accepted for all living organisms, these include Monera, Protista, Fungi, Plantae and Animalia.

 1.  Kingdom Monera (Prokaryotes)

• They are microscopic single-celled.
• Their cell wall does not contain cellulose.
• They have no definite nucleus.
• They lack most cell organelles except the ribosome.
• Reproduction is asexual by binary fission.

2. Kingdom Protista

• They are unicellular organisms.
• They are all eukaryotes i.e. cells have a definite nucleus.
• Most are aquatic organisms.
• They move either by cilia, flagella or pseudopodia.
• Some are free-living while few are parasitic.

3. Kingdom Fungi

• They are non-green organisms
• They lack chlorophyll so they do not photosynthesize.
• They are non-motile except moulds.
• They have a rigid cell wall made up of chitin and polysaccharides.
• They reproduce asexually and sexually.
• Most of them are saprophytes while some are parasites.
• They lack true roots, stem and leaves.
• Few are unicellular (yeast) while most are multicellular (rhizopus, mushroom).

4. Kingdom Plantae

This consists of organisms with cellulose cell wall and chlorophyll for manufacturing their food. It consists of three major phyla i. e Thallophyta, Bryophyta and Tracheophyta.

A. Thallophyta (algae):

Examples include spirogyra, volvox, sargassum and kelp

• These are simple aquatic photosynthetic plants
• They are non-vascular plants
• They lack true root, stem and leaves.
• They are either unicellular or multicellular and may be green, brown or red.
• They reproduce asexually (by cell division, fragmentation, spore) or sexually.

B. Bryophyta:

These include hornworts, liverworts and mosses

• They are multicellular, non-vascular plants.
• They also lack true roots, stems and leaves.
• They have chlorophyll as the only photosynthetic pigment.
• They are terrestrial but live in moist places.
• They produce spores asexually and also reproduce sexually.

C. Tracheophyta:

• They are green multicellular, terrestrial vascular plants i.e.
• They have tissues for conducting water and food.
• They have true roots, stem, and leaves.

They are subdivided into two i.e. pteridophytes and spermatophytes.

i. Pteridophyta (Ferns):

Examples include ferns etc

• They are spore-bearing plants.
• They possess well developed vascular tissues and chlorophyll
• They reproduce Asexual and sexually.
• The stem grows horizontally and is referred to as rhizome

ii. Spermatophyta:

These are seed-bearing plants. They can be grouped into two

• Gymnosperms:

Examples are (whistling pine, fir), conifers and ginkgos – Their seeds are borne naked in special structures called cones.

1. They don’t have flowers.
2. These are trees or shrubs with needle, broad or scale-like leaves.

• Angiosperms:

They form the largest group in the plants’ kingdom and are adapted to almost every kind of habitat. Examples are oil palm tree, waterleaf, maize plant etc.

1. They bear true flowers for sexual reproduction.
2. They have more abundant water-conducting vessels than gymnosperms.
3. They bear seeds enclosed in fruits.
4. They show more specialized and complex reproductive mechanism involving pollination and fertilization.

Angiosperms are grouped into two, monocotyledons and dicotyledons.

• Monocotyledonous plants:

Examples include maize, guinea grass, rice, oil palm etc.

1. They have seeds with one seed leaf (cotyledon).
2. They are generally herbs with scattered vascular bundles in their stem.
3. They have leaves with parallel venation and fibrous root system.
4. They undergo hypogeal germination (i.e. their cotyledons remain below the ground at germination.)
5. They do not undergo secondary growth.

• Dicotyledonous plants:

Examples include orange, hibiscus plants etc.

1. They are more primitive angiosperms having seeds with two seed leaves
2. They have a tap root system
3. They usually undergo secondary growth
4. The leaves have veins arranged in a branched network
5. They undergo epigeal germination (i.e the cotyledons are borne above the soil).

5. Kingdom Animalia

Kingdom Animalia is composed of all. Animals. It is the largest kingdom among the five kingdoms. The different phylum of the animal kingdom are as follows: Porifera Coelenterata (Cnidaria) Platyhelminthes Nematoda Annelida Arthropoda Mollusca Echinodermata Chordata

i. Phylum Porifera:

They are commonly known as Sponges. Main characteristics are:

• They are non-motile
• They are multicellular organisms
• They have a hard outer skeleton.
• They have a porous body.

ii. Phylum Coelenterata (Cnidaria):

Their characteristics include

• Have a hollow body cavity.
• The body is differentiated into two ends.
• The body is made of two layers of cells:
• They live in colonies (corals) as well as solitary (Sea anemone)e.g Hydra, Jellyfish, etc.

iii. Phylum Platyhelminthes:

Platyhelminthes are commonly known as flatworms. Their features are:

• Dorsoventrally flattened body.
• Complex and differentiated body structure.
• Three layers of cells and are triploblastic.
• They don’t have true internal cavity or coelom.
• Have bilateral symmetry. Eg Either free-living (Planaria) or parasitic (liver flukes).

iv. Phylum Nematoda:

This Phylum consists of roundworms. Their features are:

• They have a cylindrical body.
• They are bilaterally symmetrical and triploblastic.
• They have a false body cavity.
• They are Parasitic and cause diseases such as elephantiasis, ascariasis, etc. Eg. Ascaris

v. Phylum Annelida:

Annelids have a segmented body. They have the following features:

• They have a segmented cylindrical body.
• Their body is differentiated into head and tail.
• They are bilaterally symmetrical and triploblastic.
• Have a true body cavity. Eg. Earthworm

vi. Phylum Arthropoda:

This phylum consists of animals with jointed appendages, it is the largest phylum in the animal kingdom. Their features are:

• They are bilaterally symmetrical.
• They Have jointed appendages,
• They have an exoskeleton and a segmented body.
• They have well-differentiated organ and organ systems.
• They have an open circulatory system, but no blood vessels. Eg grasshopper, etc.

vii. Phylum Mollusca:

Phylum Mollusca consists of a large group of animals. Features are:

• They are bilaterally symmetrical and triploblastic.
• They have a less segmented body.
• They have a well-developed organ and organ system.
• They have an open circulatory system.
• Limbs are present. Eg snails, octopus etc.

viii. Phylum Echinodermata:

Echinoderms are spiny-skinned animals. They have the following features:

• They are radially symmetrical and triploblastic.
• They have a true coelom.
• They have hard skeletal structure.
• They are free-living marine animals. Eg starfish

ix. Phylum Chordata:

The Chordates possess the following characteristics:

• They are bilaterally symmetrical and triploblastic.
• They are at an organ-system level of classification.
• They possess a notochord and a nerve cord.
• Their circulatory system is closed type.

Phylum Chordata can be divided into the following sub-phyla:

• Urochordata
• Cephalochordata
• Vertebrata

 

In our next class, we will be talking about the Organisation of Life.  We hope you enjoyed the class.

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