Notes on Chapter 7: Diversity in Living Organisms-Class 9 Science | CBSE Class 9 Biology Notes
The world around us is filled with a huge variety of living things — from tiny bacteria to tall trees and giant animals. To study and understand this vast diversity, scientists classify organisms into different groups based on their similarities and differences.
In this article, “Notes on Chapter 7: Diversity in Living Organisms-Class 9 Science“, you’ll learn how living beings are organized into a hierarchical classification system, starting from Kingdom Monera to Kingdom Animalia. This chapter also explains the five-kingdom classification and key characteristics of each group.
These notes provide clear, exam-focused explanations of every concept simply, making it easier for you to revise quickly and score better in CBSE Class 9 Science exams.
What is Biodiversity?
Biodiversity is the variety of all living organisms found on Earth.
What is a Megadiversity region?
The tropical regions of the earth, between the tropic of Cancer and the tropic of Capricorn, are rich in diversity of plant and animal life. These areas are known as regions of megadiversity.
Need for Classification
We cannot study millions of life forms one by one—it would take too long! Instead, we look for similarities among organisms to group them into classes. This makes studying life much easier and more organized.
Why do we classify organisms?
- To make the study of living organisms easier and systematic.
- To understand relationships among different groups.
- To identify and name organisms correctly.
- To understand relationships and evolution among organisms.
Early Classification Attempts
The Greek thinker Aristotle tried classifying animals based on their habitat:
- Animals living on land
- Animals living in water
- Animals living in the air
Problem with this method: Animals in the same habitat can be completely different. For example, the sea has corals, whales, octopuses, starfish, and sharks—they share only their habitat but are otherwise very different from each other.
What Does “Characteristic” Mean?
A characteristic is a particular form or function of an organism. Examples:
- Having five fingers on each hand (form)
- Ability to run (function)
Basis of Classification
Scientists classify organisms based on several fundamental characteristics:
| Basis | Example / Explanation |
|---|---|
| Cell type | Prokaryotic (no nucleus) or Eukaryotic (with nucleus) |
| Body organisation | Unicellular (one cell) or Multicellular (many cells) |
| Mode of nutrition | Autotrophic (make own food) or Heterotrophic (depend on others) |
| Presence of cell wall | Present in plants, absent in animals |
| Level of body organisation | Simple (sponges) → Complex (vertebrates) |
Classification and Evolution
What is Evolution?
Evolution is the process where life forms accumulate changes in their body design over time. These changes help organisms survive better in their environment.
- Charles Darwin first described evolution in 1859 in his famous book The Origin of Species.
“Primitive” vs. “Advanced” Organisms
Organisms with an ancient body design that haven’t changed much over time are called “primitive” or “lower” organisms.
Organisms that have acquired their body designs relatively recently are called “advanced” or “higher” organisms
Hierarchy of Classification
Carolus Linnaeus is known as the father of taxonomy.
Biologists classify all living organisms on the basis of a hierarchy of characteristics from large groups to smaller groups. The levels are:
- Kingdom (largest group)
- Phylum (for animals) / Division (for plants)
- Class
- Order
- Family
- Genus
- Species (smallest group – the basic unit)
What is a Species?
A species includes all organisms that are similar enough to breed with each other and produce offspring.
Biologists Robert Whittaker (1959) proposed the Five Kingdom Classification:
- Monera
- Protista
- Fungi
- Plantae
- Animalia
These kingdoms are based on:
- Cell structure
- Mode of nutrition
- Source of nutrition
- Body organization
Carl Woese later divided Monera into two groups:
- Archaebacteria (or Archaea)
- Eubacteria (or Bacteria)
Characteristics of the Five Kingdoms of Living Organisms – Class 9 Science Notes
1. Kingdom Monera
- These organisms are prokaryotic.
- They are unicellular.
- Some of them have cell walls, while some do not.
- Their mode of nutrition can be autotrophic or heterotrophic.
Examples: Bacteria, Cyanobacteria (blue-green algae), Mycoplasma.
2. Kingdom Protista
- These organisms are unicellular eukaryotic organisms.
- Some have cilia or flagella that help in movement.
- Their mode of nutrition can be autotrophic or heterotrophic.
- Most members live in water.
- Reproduction mostly occurs through cell division.
Examples: Unicellular algae, diatoms, and protozoans (Amoeba, Paramecium, Euglena)
3. Kingdom Fungi
- These organisms are heterotrophic eukaryotes
- They absorb food from dead or decaying organic matter. Hence, they are called saprophytes.
- Their cell wall is made of chitin (a tough, complex sugar).
- Some fungi live with blue-green algae in a relationship called symbiotic. These combined life forms are called lichens.
- Reproduction occurs by Asexual spores.
- The body is often made of thread-like structures called hyphae.
Examples: Yeast, Mushroom, Penicillium.
4. Kingdom Plantae
- These are multicellular eukaryotes.
- They have cell walls made of cellulose.
- They are autotrophs and use chlorophyll for photosynthesis.
- The body is usually well-differentiated into roots, stems, and leaves.
- Reproduction occurs through seeds or spores.
Examples: Algae, Ferns, Pines, Mango Tree.
5. Kingdom Animalia
- These organisms are multicellular eukaryotes
- They do not have cell walls
- They are heterotrophs,
- A well-developed nervous and muscular system helps in movement.
- Reproduction is usually sexual, and most animals are motile.
- The body shows complex organization and specialized organs.
Examples: Human, Dog, Fish, Bird.
Summary Table of Five Kingdom
Divisions of Kingdom Plantae – Class 9 Science Notes
How Plants Are Classified
Plants are classified based on several important features:
- Whether the plant body has well-differentiated, distinct parts
- Whether the plant has special tissues to transport water and other substances
- Whether the plant can bear seeds
- Whether the seeds are enclosed within fruits
The five main divisions are Thallophyta, Bryophyta, Pteridophyta, Gymnosperms, and Angiosperms.
1. Thallophyta (Algae)
- These plants do not have well-differentiated body parts
- They lack clear roots, stems, and leaves.
- The plants in this group are commonly called algae.
- Most of them live in water (aquatic).
- A thallus-like body performs all basic functions.
- Vascular tissues (xylem and phloem) are absent.
- Chlorophyll are present.
- Reproduction mainly takes place by spores.
Examples: Spirogyra, Ulothrix, Chara.
2. Bryophyta (Mosses)
- These plants are called the “amphibians of the plant kingdom“, as can live both in water and on land
- Their body has stem-like and leaf-like structures, but true roots are absent.
- They do NOT have specialized tissues (Vascular tissues) for transporting water.
- The anchoring structure is called a rhizoid.
- Reproduction occurs by spores.
- The plants are generally found in moist and shady habitats.
Examples: Marchantia, Funaria (Moss), Riccia.
3. Pteridophyta (Ferns)
- These plants have a well-differentiated body with roots, stems, and leaves.
- They have specialised Vascular tissues (xylem and phloem).
- Reproduction takes place by spores.
- The plants prefer damp and shady areas.
- The life cycle shows a clear alternation of generations.
Examples: Fern, Marsilea, Horsetail.
Define Spores.
The thallophytes, the bryophytes and the pteridophytes have naked embryos that are called spores.
Define Cryptogamae
The word “Cryptogamae” comes from two Greek words:
- “Kryptos” → hidden
- “Gamos” → marriage (or reproductive organs)
Cryptogamae are plants with hidden reproductive organs. They do not produce flowers or seeds. They reproduce by spores.
Define Phanerogams
The word “Phanerogamae” comes from the two Greek words:
- “Phaneros” → visible
- “Gamos” → marriage (reproductive organs)
Plants with well-developed reproductive tissues that make seeds are called phanerogams.
What are seeds?
- Seeds are the result of the reproductive process.
- They consist of the embryo along with stored food, which serves for the initial growth of the embryo during germination.
Phanerogams are divided into two groups : gymnosperms and angiosperms, based on whether seeds are naked or enclosed in fruits
4. Gymnosperms (Naked Seed Plants)
The word “ Gymnosperms ” comes from the two Greek words:
- “gymno” → naked
- “sperma” → seed.
- These plants bear naked seeds. Seeds are not enclosed within fruits.
- They are usually woody, evergreen and perennial in nature.
- The body shows a well-developed vascular system.
- The plants do not bear flowers.
- Reproduction takes place through cones that bear seeds openly.
Examples: Pine, Cycas, Deodar.
5. Angiosperms (Flowering Plants)
The word “ Angiosperms ” comes from the two Greek words:
- “angio” → covered
- “sperma” → seed.
- These plants have seeds that develop inside fruits.
- These are flowering plants.
- Their seeds have structures called cotyledons (seed leaves)
- Angiosperms are divided into two main groups based on the number of cotyledons:
🌾 Monocots → Seeds with one cotyledon.
🌻 Dicots → Seeds with two cotyledons.
- Vascular tissues are fully developed in these plants.
Examples: Sunflower, Rose, Mango, Rice.
What are cotyledons?
- Cotyledons are “seed leaves”
- They often emerge and turn green when seeds germinate
- They represent a bit of pre-designed plant in the seed
Types of Angiosperms:
Summary Table: Divisions of Plantae
Characteristics of Major Classes of Kingdom Animalia – Class 9 Science Notes
Animals share the following basic features:
- They are eukaryotic.
- They are multicellular.
- They are heterotrophic.
- Their cells do not have cell walls.
- Most animals can move from place to place.
They are divided into several groups based on body structure, symmetry, body cavity, and level of development.
The Ten Major Animal Groups
1. Porifera (Sponges)
The word “Porifera” means organisms with holes or pores.
- These animals are non-motile (cannot move).
- They attach to solid surfaces like rocks.
- Their body has holes all over that lead to a canal system, which circulates water. This water brings in food and oxygen.
- They have a hard outer layer or skeleton for protection.
- Their body has very minimal tissue differentiation.
- They are commonly called sponges.
- They are mainly found in marine (sea)habitats.
Examples: Sycon, Spongilla, Euplectella
2. Coelenterata (Cnidaria)
- These animals live in water.
- They have a body cavity (coelom).
- Their body is made of two layers of cells (diploblastic):
- Outer layer (outside of body)
- Inner layer (inside lining)
- Some species live in colonies (like corals), while others are solitary (like Hydra).
- The body shows radial symmetry.
Examples: Hydra, Jellyfish, Sea anemone
3. Platyhelminthes (Flatworms)
- They are bilaterally symmetrical (left and right halves are mirror images)
- They are triploblastic ( the body has three layers of cells).
- There is some degree of tissue formation.
- They do NOT have a true body cavity (coelom)
- Their body is flattened from top to bottom (dorsiventrally), so they are called flatworms.
- They are either free-living or parasitic.
Examples:
- Free-living: Planaria
- Parasitic: Liver fluke, tapeworm
4. Nematoda (Thread-like)
- These animals are bilaterally symmetrical and triploblastic.
- Their body are cylindrical rather than flattened.
- They have tissues but no real organs
- They have a pseudo-coelom (false body cavity)
- Most are parasitic worms that cause diseases
Examples:
- Ascaris (roundworm/pinworm in intestines)
- Wuchereria (filarial worms causing elephantiasis)
4. Annelida (Segmented Worms)
- These animals are bilaterally symmetrical and triploblastic.
- They have a true body cavity (coelom). This allows true organs to develop inside the body.
- The body shows extensive organ differentiation.
- Their body is divided into segments. Segments are arranged one after another from head to tail — known as metameric segmentation.
- These animals are found in freshwater, marine water, and on land.
Examples: Earthworm, Leech, Nereis.
6. Arthropoda (Jointed-Leg Animals)
The word Arthropoda means “jointed legs”.
- This is the largest group of animals in the animal kingdom.
- These animals are bilaterally symmetrical and segmented.
- They have an open circulatory system ( meaning blood does not flow in well-defined blood vessels ).
- The body cavity is filled with blood.
- They have jointed legs.
Examples: Prawn, Butterfly, Housefly, Spider, Scorpion, Crab.
6. Mollusca (Soft-bodied Animals)
- These animals are bilaterally symmetrical.
- The coelomic cavity is present but reduced in size.
- The body shows very little segmentation.
- They have an open circulatory system
- They have kidney-like organs for excretion.
- They have a muscular foot for moving around,
Examples: Snail, Mussel, Octopus, Pila, Unio.
8. Echinodermata (Spiny-Skinned Animals)
The word “Echinodermata” comes from two Greek words: “Echinos” means hedgehog, and “Derma” means skin. Thus, these are spiny-skinned organisms.
- These are exclusively free-living marine animals.
- They are triploblastic and have a true coelomic cavity.
- They have a unique water-driven tube system for movement.
- They also have a hard calcium carbonate structure that they use as a skeleton.
- The body shows radial symmetry in adults and bilateral symmetry in larvae.
Examples: Starfish, Sea urchin, Sea cucumber.
9. Protochordata (Primitive Chordates)
- These animals are bilaterally symmetrical, triploblastic, and have a coelom.
- They have a notochord at least at some stage in their life.
- The notochord is a rod-like supporting structure that runs along the back of the animal. It separates the nerve tissue from the gut and provides support for muscle attachment for ease of movement.
- The notochord may not extend through the entire body or may be present only in certain life stages.
- All protochordates are marine animals.
Examples: Balanoglossus, Herdmania, Amphioxus.
10. Vertebrata (Animals with Backbone)
- These animals have a true vertebral column (backbone) and an internal skeleton. This allows better muscle attachment for movement.
- Vertebrates are bilaterally symmetrical, triploblastic, coelomic, and segmented.
- They show complex differentiation of tissues and organs.
All chordates (including vertebrates) possess the following features:
(i) have a notochord
(ii) have a dorsal nerve cord
(iii) are triploblastic
(iv) have paired gill pouches
(v) are coelomate ( a body cavity )
Examples: Fish, Frog, Snake, Bird, Human.
Vertebrates are grouped into five classes: Pisces, Amphibia, Reptilia, Aves, and Mammalia.
Summary Table: Classes of Animalia
Sub-Classes of Vertebrata – Class 9 Science Notes
Vertebrates are divided into five major sub-classes: Pisces, Amphibia, Reptilia, Aves, and Mammalia.
1. Pisces (Fish)
- These are fish, and they are exclusively aquatic animals.
- The skin is covered with scales or plates.
- They breathe using gills (get oxygen from water)
- The body is streamlined, and a muscular tail is used for movement.
- They are cold-blooded animals ( body temperature changes with the environment).
- The heart has two chambers (one atrium and one ventricle).
- They lay eggs.
Types:
- Some have skeletons made entirely of cartilage (sharks, rays)
- Some have skeletons made of bone and cartilage (rohu, tuna)
Examples: Shark, Rohu, Tuna, Catfish.
2. Amphibia (Frogs and Salamanders)
- These animals are called amphibians because they can live both in water and on land.
- They do NOT have scales.
- They have mucus glands in their skin.
- Their heart has three chambers.
- They breathe through gills or lungs.
- They lay eggs.
- They are cold-blooded animals
Examples: Frog, Toad, Salamander.
3. Reptilia (Reptiles)
- These animals are cold-blooded.
- They have scales on their body.
- They breathe through their lungs.
- Most reptiles have a three-chambered heart, but crocodiles have a four-chambered heart.
- They lay eggs on land with tough coverings (unlike amphibians).
Examples: Snake, Lizard, Turtle, Crocodile.
4. Aves (Birds)
- These animals are warm-blooded( meaning their body temperature stays constant regardless of the surroundings).
- They have a four-chambered heart
- They lay eggs.
- Their body is covered with feathers.
- Their two forelimbs are modified into wings for flight.
- They breathe through their lungs.
- All birds fall in this category.
Examples: Crow, Pigeon, Sparrow, Parrot, Eagle.
5. Mammalia (Mammals)
- Mammals are warm-blooded animals with four-chambered hearts.
- They have mammary glands that produce milk to feed their young ones.
- Their skin has hair, sweat glands, and oil glands.
- Most mammals give birth to live young ones (viviparous).
- However, a few mammals lay eggs, such as: Platypus and Echidna
- Some mammals, like kangaroos, give birth to very poorly developed young ones.
- They are found in all types of habitats — land, air, and water.
- The body shows highly developed organ systems.
Examples: Humans, cows, dogs, cats, whales, bats, rats.
Summary Table: Sub-Classes of Vertebrata
Special Note: Carolus Linnaeus
Who was he?
- Carolus Linnaeus (1707-1778) was born in Sweden.
- He was a doctor by profession.
His Contribution:
- He published the famous book “Systema Naturae”
- He is known as the “father of modern taxonomy”.
NCERT Notes for Class 9 Science
- Chapter 1 Matter in Our Surroundings Class 9 Notes
- Chapter 2 Is Matter Around Us Pure Class 9 Notes
- Chapter 3 Atoms and Molecules Class 9 Notes
- Chapter 4 Structure of the Atom Class 9 Notes
- Chapter 5 The Fundamental Unit of Life Class 9 Notes
- Chapter 6 Tissues Class 9 Notes
- Chapter 7 Diversity in Living Organisms Class 9 Notes
- Chapter 8 Motion Class 9 Notes
- Chapter 9 Force and Laws of Motion Class 9 Notes
- Chapter 10 Gravitation Class 9 Notes
- Chapter 11 Work, Power And Energy Class 9 Notes
- Chapter 12 Sound Class 9 Notes
- Chapter 13 Why Do we Fall ill Class 9 Notes
- Chapter 14 Natural Resources Class 9 Notes
- Chapter 15 Improvement in Food Resources Class 9 Notes