Diversity in Living Organisms

Classification of organisms helps us to:

• Study a large variety of organisms systematically
• Understand similarities and differences among organisms
• Identify organisms easily
• Trace evolutionary relationships
• Predict characteristics of newly discovered organisms

The characteristic that affects the basic body design and functions of an organism should be preferred.

Fundamental characteristics like cell structure or mode of nutrition are chosen over superficial ones like colour or habitat.

Organisms are grouped into five kingdoms based on:

• Type of cell (prokaryotic or eukaryotic)
• Number of cells (unicellular or multicellular)
• Presence or absence of cell wall
• Mode of nutrition (autotrophic or heterotrophic)
• Level of body organisation

The major divisions in Plantae are:

• Thallophyta
• Bryophyta
• Pteridophyta
• Gymnosperms
• Angiosperms

These divisions are based on:
• Level of body differentiation
• Presence of vascular tissues
• Presence of seeds
• Whether seeds are naked or enclosed

In plants, classification is mainly based on:
• Body differentiation
• Presence of vascular tissues
• Seed formation

In animals, classification is based on:
• Body symmetry
• Type of body cavity (coelom)
• Segmentation
• Presence of notochord

Vertebrates are classified into subgroups based on:

• Presence of jaws
• Type of respiration (gills or lungs)
• Body covering (scales, feathers, hair)
• Reproductive methods (egg-laying or giving birth)
• Number of heart chambers

The main vertebrate classes are:
Pisces, Amphibia, Reptilia, Aves, and Mammalia.