CBSE Class 9 Science Chapter 7: Diversity in Living Organisms Revision Notes

The Basis of Classification and Evolutionary Connections

The classification of living organisms is not arbitrary; it is based on evolutionary relationships and structural complexities. In 1969, Robert Whittaker proposed the Five Kingdom Classification, which divides all living organisms into Monera, Protista, Fungi, Plantae, and Animalia. The primary characteristics used for this division include:

1. Cell Type: Whether the cells are prokaryotic (lacking a defined nucleus and membrane-bound organelles) or eukaryotic (having a true nucleus).
2. Body Organization: Whether the organism is unicellular or multicellular.
3. Mode of Nutrition: Whether they synthesize their own food (autotrophic) or depend on others (heterotrophic).

This classification mirrors evolution. Charles Darwin first introduced the concept of evolution in his book The Origin of Species in 1859. Organisms with older, simpler body designs are termed primitive (lower) organisms, while those with more recent, complex structural changes are called advanced (higher) organisms. Thus, classification acts as a direct map of evolutionary history.

Essential Terminology Glossary

Prokaryotes

Organisms that lack a well-defined nucleus and membrane-bound cell organelles (e.g., bacteria in Kingdom Monera).

Eukaryotes

Organisms with cells containing a membrane-bound nucleus and specialized organelles.

Lichen

A symbiotic, mutually beneficial association between an alga (autotroph) and a fungus (heterotroph).

Coelom

The main fluid-filled body cavity located between the body wall and the digestive tract, lined by mesoderm.

Bilateral Symmetry

A body design where the left and right halves of the body have the same design (e.g., humans, arthropods).

Triploblastic

Organisms having a body derived from three embryonic germ layers: ectoderm, mesoderm, and endoderm.

Notochord

A long, rod-like support structure that runs along the back of chordates, separating the nervous tissue from the gut.

Major Differences: Non-Chordates vs. Chordates

Taxonomic Hierarchy and Binomial Nomenclature

1. —
2. —
3. —
4. —
5. —
6. —
7. —
8. —
9. —

Must Remember Key Points

• Kingdom Monera contains unicellular, prokaryotic organisms like bacteria, blue-green algae (cyanobacteria), and mycoplasma.
• Kingdom Protista contains unicellular, eukaryotic organisms; they use appendages like cilia or flagella for locomotion.
• Kingdom Fungi consists of saprophytic, eukaryotic organisms with cell walls made of a tough complex sugar called chitin.
• Bryophytes are called the 'amphibians of the plant kingdom' because they require water to complete their sexual life cycle.
• Pteridophytes are the first terrestrial plants to possess specialized vascular tissues (xylem and phloem) for water and food conduction.
• Gymnosperms bear naked seeds (non-flowering, e.g., Pinus), whereas Angiosperms bear seeds enclosed inside fruits (flowering plants).
• Arthropoda is the largest phylum in the animal kingdom, characterized by jointed appendages and an open circulatory system.
• Warm-blooded organisms (Aves and Mammals) can maintain a constant body temperature, whereas cold-blooded ones (Pisces, Amphibia, Reptilia) depend on environmental temperatures.

Board Exam Traps & Writing Cues

1. Scientific Names Trap: Never forget to underline the Genus and Species separately when writing them in exams. For example, write Homo sapiens with individual underlines. Do not draw a single continuous line underneath both words!

2. Bryophyte vs. Pteridophyte: Examiners love asking about vascular tissues. Remember: Bryophytes do NOT have specialized vascular systems, whereas Pteridophytes are the first to develop them.

3. Coelom Classification: Pay close attention to phylum-level differences: Platyhelminthes are acoelomate (no cavity), Nematodes are pseudocoelomate (false cavity), and Annelids onwards are true coelomates. This is a very common multiple-choice and short-answer target.

Quick Revision Check

• Why are bats and whales classified as mammals despite not looking like terrestrial quadrupeds? Bats and whales are mammals because they possess mammary glands for producing milk to nourish their young, are warm-blooded, have a four-chambered heart, and possess hair/sweat glands (vestigial or reduced in whales) on their body.
• What is the primary difference between Gymnosperms and Angiosperms? Gymnosperms bear naked seeds that are not enclosed inside fruits (e.g., pines, deodar), whereas Angiosperms are flowering plants whose seeds develop inside an ovary, which later matures into a fruit.
• How do bilateral symmetry and radial symmetry differ? In bilateral symmetry, the body can be divided into identical left and right halves along only one plane (e.g., humans). In radial symmetry, the body can be divided into identical halves by any plane passing through the central axis (e.g., starfish).
• Identify the phylum of an organism that has a chitinous exoskeleton, jointed appendages, and an open circulatory system. The organism belongs to the Phylum Arthropoda.

Frequently Asked Questions