Diversity in Living Organisms – Study module with Revision Notes

Revision Notes — Diversity in Living Organisms

Overview: Diversity in living organisms refers to the enormous variety of living forms found in nature. This diversity is observed in the shape, size, structure, mode of nutrition, habitat, behaviour and other biological features. Classifying this diversity helps scientists study organisms systematically, identify relationships and make sense of the natural world.

1. Need for Classification

Classification is the process of arranging organisms into groups or categories on the basis of similarities and dissimilarities. The major reasons for classification are:

• To provide a systematic order for naming and identifying organisms.
• To show evolutionary relationships among organisms.
• To make study and communication easier by grouping similar organisms together.
• To help in predicting characteristics of newly discovered organisms by placing them in existing groups.

2. Early Systems and Limitations

Early classification proposed simple two-kingdom systems (Plants and Animals). This system grouped organisms broadly but failed to account for microorganisms, fungi, and other life forms that did not fit neatly into either group. As knowledge of microscopic life and details of cell structure increased, more refined systems became necessary.

3. Five-Kingdom Classification

The five-kingdom system, widely used at the school level, divides organisms into the following kingdoms:

1. Monera: Unicellular prokaryotic organisms (bacteria, blue-green algae/ cyanobacteria). They lack membrane-bound nucleus and organelles.
2. Protista: Mostly unicellular eukaryotes (e.g., Amoeba, Paramecium, Euglena). They have a true nucleus and organelles.
3. Fungi: Multicellular or unicellular eukaryotic organisms (e.g., yeast, mushrooms). They are heterotrophic, absorb nutrients and have cell walls made of chitin.
4. Plantae: Multicellular, photosynthetic organisms with cell walls made of cellulose (e.g., mosses, ferns, flowering plants).
5. Animalia: Multicellular, heterotrophic organisms without cell walls (e.g., sponges, insects, mammals).

Each kingdom is characterised by certain defining features such as cell type, mode of nutrition, body organisation and reproduction.

4. Hierarchical Classification

The hierarchical system arranges organisms into successive categories. The major taxonomic ranks — from broad to specific — are:

Kingdom > Phylum (Division for plants) > Class > Order > Family > Genus > Species

For example, the housefly has a classification that becomes more specific at each rank. The species is the basic unit; organisms of the same species can interbreed and produce fertile offspring.

5. Basis of Classification

Organisms are classified on the basis of many characters such as:

• Cell structure (prokaryote/eukaryote)
• Body organisation (unicellular/multicellular)
• Mode of nutrition (autotrophic/heterotrophic/parasite)
• Reproduction (sexual/asexual)
• Presence of cell wall and chemical composition
• Morphology, anatomy and life cycles

6. Plant Kingdom — Major Groups (Overview)

The plant kingdom is divided into groups showing increasing complexity. A brief overview of major plant groups is given below.

• Algae: Simple photosynthetic organisms; can be unicellular or multicellular (e.g., Chlamydomonas, Spirogyra, Ulothrix). They live in aquatic habitats and show a variety of reproductive strategies.
• Bryophytes: Non-vascular plants (mosses, liverworts). They lack true roots, stems and leaves and are usually found in moist habitats.
• Pteridophytes: Vascular plants reproducing via spores (e.g., ferns). They have true roots, stems and leaves.
• Gymnosperms: Seed-producing plants where seeds are not enclosed in fruits (e.g., pines, cedars).
• Angiosperms: Flowering plants producing seeds enclosed in fruits. They are the most advanced and diverse group (divided further into monocots and dicots).

7. Animal Kingdom — Major Groups (Overview)

Animals are classified into major groups (phyla) based on body organisation, symmetry, presence of body cavity, segmentation and other features. A brief list of important phyla:

• Porifera: Sponges — simplest animals with pores and channels.
• Coelenterata/Cnidaria: Jellyfish, hydra — radial symmetry and specialized stinging cells.
• Platyhelminthes: Flatworms — bilateral symmetry and flattened body.
• Nematoda: Roundworms — cylindrical bodies with complete digestive tract.
• Annelida: Segmented worms (earthworm) — segmentation and closed circulatory system.
• Arthropoda: Insects, spiders, crustaceans — jointed appendages and exoskeleton.
• Mollusca: Snails, octopus — soft-bodied, often with shell.
• Echinodermata: Starfish — radial symmetry in adult stage and water vascular system.
• Chordata: Animals with notochord at some stage (includes fishes, amphibians, reptiles, birds, mammals).

8. Viruses, Bacteria and Lichens

Bacteria (Monera): Microscopic prokaryotes with diverse modes of nutrition: autotrophs (photosynthetic bacteria), heterotrophs, decomposers and some pathogens.

Viruses: Acellular entities; contain either DNA or RNA and require host cells to reproduce. Viruses do not fit neatly into the five-kingdom scheme; they are studied separately due to their acellular nature.

Lichens: Symbiotic association between a fungus and an alga or cyanobacterium. Lichens are important bioindicators of air quality.

9. Distinguishing Features & Examples

Learning characteristic features and a few representative examples for each major group is the quickest way to prepare for examinations. Below are compact notes to memorise:

10. Diagrams to Practice

Draw and label the following to score marks in diagram-based questions:

• Structure of Amoeba (showing pseudopodia, nucleus, contractile vacuole).
• Structure of a typical flowering plant (label root, stem, leaf, flower parts).
• Life cycle/sketch of alternation of generations (simple schematic for plants).
• Representative animal body plan (earthworm segmentation, insect body parts).

11. Quick Revision Checklist (Very Useful before exams)

1. Understand the five kingdoms and their main features.
2. Memorise distinguishing features and examples for major plant and animal groups.
3. Be able to explain why classification is required and limitations of old systems.
4. Practise labelling diagrams and writing short definitions (e.g., taxonomy, species).
5. Go through NCERT textbook exercises and sample questions; write answers in point form.

12. Important Terms & Definitions

13. Sample Questions (Practice)

14. How to Study This Chapter Effectively

• Read NCERT text carefully and underline definitions and examples.
• Create a table summarising characteristics and examples of each kingdom — tables are quick to memorise.
• Use flowcharts to represent hierarchical classification — visual memory helps retention.
• Practice drawing labelled diagrams — even simple neat sketches fetch marks.
• Solve NCERT exercise questions and attempt one sample long answer every week.

15. Common Mistakes & How to Avoid Them

• Mixing up features of fungi and plants — remember fungi are heterotrophic and have chitin in cell wall.
• Forgetting to mention one or two key distinguishing characters in short answer questions — always list features pointwise.
• Poor labelling in diagrams — practise neat labels and use arrows clearly.

16. Sample Answer Template (for long/structured answers)

17. Revision Activities & Practical Ideas

• Visit a local pond or garden and observe algae, mosses and flowering plants; note distinguishing features.
• Collect images or draw simple diagrams for one representative from each major group and make a flashcard set.
• Make a two-column table: Group | Key features | Example — use as a one-page revision sheet.

18. Final Tips Before the Exam

• Make a one-page summary that includes kingdom names, 2–3 features each and 1 example each.
• Memorise key definitions and practice at least three diagrams neatly.
• Attempt previous year/sample questions under timed conditions to manage time during exams.

Prepared as an NCERT-aligned study module for CBSE Class 9 — Chapter 13: Diversity in Living Organisms. Use this HTML directly within the WordPress editor (Text/HTML mode).