Diversity in Living Organisms Class 9 Notes

Diversity in Living Organisms Class 9 Notes – A summary and revision notes for Class 9 Science Chapter 7, Diversity in Living Organisms, are provided here. The entire chapter’s major points, revision comments, pictures, and diagrams are included in the notes. Students studying science with the NCERT Textbook and looking for a quick approach to learn the crucial facts will find these notes useful.

Diversity in Living Organisms Class 9 Notes

What is Diversity?

The diversity of life on Earth, is also known as biodiversity, refers to ecosystems of earth, the wide variety of species, and genetic variations found in both the animal kingdoms and plant. This diversity is essential to the health of ecosystems and the services they provide, pollination, temperature regulation and including soil formation.


Living things can adapt to their environment through the gradual process of evolution in order to survive. As a result, the ecosystem becomes more diverse and new species are eventually created.

What is the Basis of Classification?

Studying each living thing separately might be difficult because of the huge variety of living things. Animals and plants were divided into categories and subcategories to facilitate the study. Animals that lived in water or on land were separated into two groups by Aristotle according to their habitat.

The restrictions of Aristotle’s classification, which divided creatures into aquatic and terrestrial species based on their habitat, were insufficient. From small organisms like sea horses to enormous ones like whales, both land and marine settings are home to a diversity of animals and plants. It was therefore a poor method of classification.

Modern classification of living organisms considers various interrelated characteristics, starting with the nature of the cell. Some of these characteristics include:

  • The presence of a nucleus and membrane-bound organelles in eukaryotic cells, which enables efficient cellular processes and allows for multicellular organisms.
  • The arrangement of cells in an organism, whether they are single or grouped together to form a single entity with division of labor among cells.
  • The ability of organisms to produce their own food through photosynthesis, which affects their body design.
  • The level of organization of the body in photosynthetic organisms (plants).
  • The development and organization of the body in animals, including specialized organs for different functions.

Classification and Evolution

In 1859, Charles Darwin published a book called “Origin of Species” in which he presented his theories of evolution. According to these theories, all living organisms have evolved from single-celled organisms. Simple body designs appeared early in evolutionary history, leading to more intricate designs, resulting in a vast diversity of life forms. All organisms are interconnected due to their common ancestry, and the closer evolutionary relationship between two organisms is also used as a basis for classifying them.

The Hierarchy of Classification Groups

Biologists, including Ernst Haeckel (1894), Robert Whittaker (1969), and Carl Woese (1977), have attempted to divide all living organisms into broad categories referred to as kingdoms. Whittaker’s classification, which includes five kingdoms: Monera, Protista, Fungi, Plantae, and Animalia, is widely used and is based on the organisms’ cell structure, mode of nutrition, and body organization. Woese’s modification, which divides the Monera into Archaebacteria (or Archaea) and Eubacteria (or Bacteria), is also in use.

Whittaker’s Five Kingdom Classification
whittakers classification
Whittaker’s Classification
Further Levels of Classification

Additional categorization is performed by naming the subgroups at various levels as outlined in the following scheme.

further levels of classification
Further Levels of Classification
  1. Kingdom: The highest level of classification, consisting of a number of phyla or divisions (in the case of plants) with similar characteristics.
  2. Phylum/Division: A level of classification consisting of a number of classes with similar characteristics.
  3. Class: A level of classification consisting of a number of orders with similar characteristics.
  4. Order: A level of classification consisting of a number of families with similar characteristics.
  5. Family: A level of classification consisting of a number of genera with similar characteristics.
  6. Genus: A level of classification consisting of a number of species with similar characteristics.
  7. Species: The lowest level of classification, consisting of a number of organisms with similar characteristics that can interbreed and produce a fertile offspring.
  • These are unicellular organisms that lack a defined nucleus or membrane-bound organelles.
  • Some organisms in this group have a cell wall.
  • They can obtain nutrition either by producing their own food (autotrophic) or by acquiring it from their surroundings (heterotrophic).
  • Members of this group include bacteria, blue-green algae or cyanobacteria, and some types of protozoa and fungi.
  • Group: Unicellular eukaryotic organisms.
  • Some use appendages (cilia or flagella) for movement.
  • Both autotrophic and heterotrophic feeding modes are possible.
  • Examples include unicellular algae, diatoms, and protozoans.
  • Group: Heterotrophic eukaryotic organisms.
  • Some use decaying organic material as food and are called saprotrophs.
  • Others require a living host organism for food and are called parasites.
  • Some can become multicellular at certain stages in their lives.
  • They have cell walls made of chitin.
  • Examples include yeasts, molds, and mushrooms.
  • Group: Multicellular eukaryotes with cell walls.
  • They use chlorophyll for photosynthesis and are autotrophs.
  • All plants are included in this group.
  • Group: Multicellular eukaryotes without cell walls.
  • They are heterotrophs, meaning they consume other organisms for food.
  • Examples include animals, including humans.

The Five Kingdom classification



Plants are classified based on the presence or absence of distinct body parts, such as roots, stems, and leaves, which is the first level of classification. The second level is based on whether the plant body has specialized tissues for transporting water and nutrients. Further classification depends on whether the plant can produce seeds and if those seeds are enclosed in fruits.

Thallophyta or Algae – Algae are simple-bodied plants that are most frequently found in water. They don’t have the stems, roots, and leaves found in other plants. Spirogyra, Ulothrix, Cladophora, and Chora are a few types of algae.

Bryophyta – These are referred to as the amphibians of the plant kingdom because they share characteristics of both algae and more complex plants. They have a slightly differentiated body structure that includes stem and leaf-like structures, but lack specialized tissues for transporting water and nutrients. Examples of such plants are moss (Funaria) and Marchantia.

Pteridophyta – Plants that have a well-differentiated body structure consisting of roots, stems, and leaves with specialized tissues for transporting water and nutrients are classified as vascular plants. Examples of vascular plants include Marsilea, ferns, and horsetails.

Gymnosperms – Plants that belong to this group have naked seeds and are typically perennial, woody, and evergreen. They are classified as gymnosperms, meaning “naked seed.” Examples of gymnosperms include pines and deodar.

Angiosperms – The Greek terms “angio,” which means covered, and “sperma,” which means seed, are the source of the English word “angiosperm.” Because angiosperms produce flowers that turn into fruits, they’re also known as flowering plants some times.

Classification of plants

classification of plants
Classification of plants


Animals are eukaryotic, multicellular, and heterotrophic organisms that lack cell walls and are typically mobile. They are categorized based on the degree and type of differentiation in their body design.

PORIFERA – Animals with pores or holes all over their bodies are known as porifera. These organisms are sessile, meaning they stay affixed to a surface. Their bodies have a complex network of canals that aid in the circulation of water that carries food and oxygen in. These creatures have a skeleton or exterior hard coating covering their bodies.

Coelenterata (Cnidaria)
  • Coelenterates are aquatic animals.
  • They are named after the presence of a cavity in their body, which is known as a coelom.
  • The body of coelenterates is composed of two layers of cells.
  • The outer layer of cells forms the surface of the body, while the inner layer lines the coelom.
  • Some common examples of coelenterates include Hydra and jellyfish.
  • Flatworms have a body that is bilaterally symmetrical, which means the left and right halves of their body have the same structure.
  • They are referred to as triploblastic since they have three layers of cells, which can differentiate into various tissues.
  • Flatworms lack a true internal body cavity or coelom, which means they don’t have a well-developed space for organs to reside in.
  • Their body is flattened from top to bottom, which is why they are called flatworms.
  • Flatworms can be either free-living or parasitic.
  • Planaria and liver flukes are examples of flatworms.
  • Nematodes have a cylindrical body shape, rather than a flattened one.
  • They exhibit bilateral symmetry and are triploblastic, meaning they have three germ layers (endoderm, mesoderm, and ectoderm) in their embryos.
  • Nematodes have tissues, but no well-defined organs. However, they do have a body cavity called a pseudo-coelom, which is not fully lined with mesodermal tissue like a true coelom would be.
  • Some nematodes are parasitic and can cause diseases, such as filarial worms that cause elephantiasis, or roundworm and pinworm species that live in the intestines of animals (including humans).
  • Annelids are triploblastic with bilateral symmetry and a real body cavity.
  • Organ packaging and significant organ differentiation are made possible by the presence of a genuine coelom.
  • Annelids have repeated units of segments that are lined up from head to tail, showing segmental differentiation.
  • Freshwater, marine, and land habitats are just a few of the places where annelids can be found, Earthwormsand leeches are examples of Annelida.
  • The largest group of animal are arthropods.
  • They are bilaterally symmetrical and segmented, and have jointed legs, which give the phylum its name (arthropod = jointed legs).
  • Arthropods have an open circulatory system, meaning that blood is not enclosed in well-defined blood vessels. The coelomic cavity is blood-filled.
  • Arthropods include a wide variety of familiar examples, such as prawns, butterflies, houseflies, spiders, scorpions, and crabs.
  • Mollusks have limited segmentation and a small coelomic cavity, yet they also show bilateral symmetry.
  • They have kidney-like excretory organs and an open circulatory system.
  • In addition to having a foot for propulsion, mollusks frequently have a protective shell or other covering.
  • Snails and mussels are two examples of mollusks.
  • Echinoderms are spiny-skinned organisms, named after the Greek words for “hedgehog” and “skin”.
  • They are exclusively free-living marine animals and are triploblastic with a coelomic cavity.
  • Echinoderms use a peculiar water-driven tube system for moving around and have hard calcium carbonate structures that serve as a skeleton.
  • Examples of echinoderms include sea-stars and sea urchins.
  • Protochordates are triploblastic, bilaterally symmetrical creatures possessing a coelom.
  • The notochord, a long rod-like support structure that runs along the animal’s back and serves as a location for muscles to attach for simple movement, is a special characteristic of these animals.
  • It’s possible that the notochord is not always present or for the entirety of the animal’s life.
  • Marine creatures known as protochordates include Balanoglossus, Herdmania, and Amphioxus.
  • Vertebrates have a true vertebral column and internal skeleton, allowing for a different distribution of muscle attachment points for movement.
  • Vertebrates and all chordates have complex differentiation of their body tissues and organs and are bilaterally symmetrical, triploblastic, segmented, and coelomic.
  • All chordates possess certain features, including a notochord, a dorsal nerve cord, paired gill pouches, and being triploblastic and coelomate.

Vertebrates are grouped into five classes.

  • Cyclostomata – Cyclostomes are a type of jawless vertebrate with an elongated, eel-like body, circular mouth, slimy and scaleless skin. They are ectoparasites or borers of other vertebrates. Lampreys and Hagfish are examples of cyclostomes.
  • Pisces – Fish are aquatic animals that have scales/plates covering their skin and use gills to obtain oxygen dissolved in water. They have a streamlined body with a muscular tail used for movement, are cold-blooded, and have a two-chambered heart. Fish lay eggs and come in many varieties, with some having skeletons made entirely of cartilage, like sharks, and others having a skeleton made of both bone and cartilage, like tuna or rohu.
  • Amphibia – Amphibians are a group of animals that have mucus glands in their skin, lack scales, and have a three-chambered heart. They can respire through gills or lungs and lay eggs. They are found both in water and on land, with frogs, toads, and salamanders being some examples of amphibians.
  • Aves – This describes birds, which are warm-blooded, lay eggs, have a four-chambered heart, feathers for an outside covering, and modified forelimbs for flight. They breathe through lungs.
  • Mammalia – Mammals are warm-blooded animals with a four-chambered heart and skin that has hairs, sweat and oil glands. They produce milk to nourish their young through mammary glands. Most mammals give birth to live young, but some, like the platypus and the echidna lay eggs, and others, like kangaroos give birth to poorly developed young.

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