Diversity in Living Organisms

The term biodiversity refers to the variety of living organisms present on Earth.

Organisms differ in:

• size,
• shape,
• habitat,
• nutrition,
• movement,
• and reproduction.

For example:

• bacteria are microscopic,
• elephants are gigantic,
• cactus survives in deserts,
• fish survive in water.

These Class 9 Science Chapter 12 Notes explain that diversity developed gradually through evolution and adaptation to different environments.

 

Need for Classification

Classification is the process of grouping organisms based on similarities and differences.

Classification is important because it:

• simplifies study of organisms,
• helps identify organisms,
• shows relationships among organisms,
• and helps understand evolution.

Without classification, biological study would become extremely confusing.

 

Basis of Classification

Scientists use several characteristics for classification.

Important criteria include:

• cell structure,
• body organisation,
• mode of nutrition,
• habitat,
• reproduction,
• and evolutionary relationships.

Organisms with more similarities are placed closer together.

 

Hierarchy of Classification

Biological classification follows hierarchical levels.

The main taxonomic categories are:

• Kingdom,
• Phylum or Division,
• Class,
• Order,
• Family,
• Genus,
• Species.

Species is the smallest and most specific category.

Organisms belonging to the same species can reproduce and produce fertile offspring.

 

Five Kingdom Classification

R. H. Whittaker proposed the five kingdom classification system.

The five kingdoms are:

• Monera,
• Protista,
• Fungi,
• Plantae,
• Animalia.

This system classifies organisms based on:

• cell type,
• body organisation,
• nutrition,
• and reproduction.

 

Kingdom Monera

Kingdom Monera includes unicellular prokaryotic organisms.

Characteristics:

• single-celled,
• no true nucleus,
• no membrane-bound organelles.

Examples:

• bacteria,
• cyanobacteria.

Monerans are among the simplest organisms.

Some bacteria are useful, while others cause diseases.

 

Kingdom Protista

Kingdom Protista includes unicellular eukaryotic organisms.

Characteristics:

• true nucleus,
• mostly aquatic,
• simple body organisation.

Examples:

• Amoeba,
• Paramecium,
• Euglena.

Protists show both plant-like and animal-like characteristics.

 

Kingdom Fungi

Fungi are eukaryotic organisms that obtain food by absorption.

Characteristics:

• mostly multicellular,
• non-green,
• heterotrophic,
• cell wall present.

Examples:

• mushroom,
• yeast,
• bread mould.

Fungi play important roles in decomposition and nutrient recycling.

 

Kingdom Plantae

Kingdom Plantae includes multicellular green organisms capable of photosynthesis.

Characteristics:

• chlorophyll present,
• autotrophic nutrition,
• cell wall present.

Plants prepare food using sunlight.

Plants are extremely important because they produce oxygen and form the base of food chains.

 

Kingdom Animalia

Kingdom Animalia includes multicellular heterotrophic organisms.

Characteristics:

• no cell wall,
• active movement,
• complex organ systems.

Examples:

• insects,
• fishes,
• birds,
• mammals.

Animals depend directly or indirectly on plants for food.

 

Classification of Plants

Plants are classified based on:

• body structure,
• presence of vascular tissues,
• seed formation,
• and reproductive structures.

 

Thallophyta

Thallophytes have simple plant body without roots, stems, or leaves.

Examples:

• algae.

These plants are mostly aquatic.

 

Bryophyta

Bryophytes are called amphibians of the plant kingdom.

They live on land but require water for reproduction.

Examples:

• mosses,
• liverworts.

Bryophytes lack well-developed vascular tissues.

 

Pteridophyta

Pteridophytes possess vascular tissues.

Examples:

• ferns.

They reproduce through spores instead of seeds.

 

Gymnosperms

Gymnosperms are seed-producing plants with naked seeds.

Examples:

• pine,
• cycas.

Seeds are not enclosed within fruits.

 

Angiosperms

Angiosperms are flowering plants producing seeds enclosed within fruits.

Examples:

• mango,
• rose,
• wheat.

Angiosperms are the most advanced and diverse plant group.

 

Monocots and Dicots

Angiosperms are divided into:

• monocots,
• dicots.

Monocots:

• one cotyledon,
• parallel venation.

Dicots:

• two cotyledons,
• reticulate venation.

 

Classification of Animals

Animals are classified based on:

• body symmetry,
• body cavity,
• segmentation,
• and level of organisation.

 

Porifera

Porifera includes simple aquatic animals with pores on their body.

Examples:

• sponges.

These are among the simplest multicellular animals.

 

Coelenterata

Coelenterates possess a body cavity and tentacles.

Examples:

• Hydra,
• jellyfish.

They show radial symmetry.

 

Platyhelminthes

These are flatworms with bilateral symmetry.

Examples:

• tapeworm,
• planaria.

Many are parasitic.

 

Nematoda

Nematodes are cylindrical worms.

Examples:

• roundworms.

Some cause diseases in humans.

 

Annelida

Annelids are segmented worms.

Examples:

• earthworm,
• leech.

Segmentation improves movement efficiency.

 

Arthropoda

Arthropods are the largest animal group.

Characteristics:

• jointed legs,
• exoskeleton.

Examples:

• insects,
• spiders,
• crabs.

 

Mollusca

Molluscs have soft bodies.

Examples:

• snail,
• octopus.

Some possess hard shells.

 

Echinodermata

Echinoderms possess spiny skin.

Examples:

• starfish,
• sea urchin.

They are exclusively marine.

 

Pisces

Pisces are fishes.

Characteristics:

• aquatic,
• gills for respiration,
• fins for movement.

 

Amphibia

Amphibians live both on land and in water.

Examples:

• frogs,
• salamanders.

They require water for reproduction.

 

Reptilia

Reptiles possess dry scaly skin.

Examples:

• snakes,
• lizards,
• crocodiles.

Most reptiles lay eggs.

 

Aves

Aves are birds.

Characteristics:

• feathers,
• wings,
• warm-blooded.

Birds are adapted for flight.

 

Mammalia

Mammals possess mammary glands.

Characteristics:

• hair present,
• warm-blooded,
• most give birth to young ones.

Examples:

• humans,
• cows,
• whales.

 

Evolution and Classification

Classification also reflects evolutionary relationships.

Organisms sharing more similarities are believed to have common ancestors.

Thus, classification helps scientists study evolution scientifically.

 

Binomial Nomenclature

Scientific naming uses binomial nomenclature.

Each organism receives:

• genus name,
• species name.

Example:

• Homo sapiens.

This system was developed by Carolus Linnaeus.

Scientific names are universal and avoid confusion.

 

Importance of Classification

Classification:

• organises biological knowledge,
• helps identification,
• shows relationships,
• and supports scientific communication.

Modern biology depends heavily on classification systems.