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Detailed Chapter Notes - Diversity in living organisms, Class 9, Science Notes - Class 9

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Biodiversity refers to all the diverse plants, animals and micro organisms present on earth.

Biological diversity or biodiversity is the occurrence of diverse or varied forms of living beings which differ from one another in external appearance, size, colour pattern, internal structure, nutrition, behaviour, habitat, etc.

They range in size from microscopic bacteria, hardly a few micrometers in size, to Blue Whale (about 30 m in length) and Redwood trees (Sequoia) of California (about 100 m in height). Similarly some pine trees (e.g. Pinus) live for thousands of years while many insects like mosquitoes have a life span of a few days. There are transparent jelly fishes and worms on one hand to brightly coloured birds and flowers on the other hand.

It is estimated that there are at least 10 million different species of plants and animals living today, but only 1.7 million have been described so far worldwide.

Detailed Chapter Notes - Diversity in living organisms, Class 9, Science Notes - Class 9


Do you know ?

Term "Biodiversity" was coined by " Walter G. Rosen" in 1986.

Megadiversity : The warm and humid tropical regions of the earth between the tropic of Capricorn and the tropic of Cancer, are rich in diversity of plant and animal life. This is called the region of "megadiversity".

There are 12 megadiversity centres in the world, which are rich in biodiversity.

Countries are - Brazil, Colombia, Ecuador, Peru, Mexico, Zaire, Medagascar, Australia, China, Indonesia, Melaysia and India.



Classification is the arrangement of organisms into groups and subgroups on the basis of their similarities and dissimilarities.



Taxonomy: : The science dealing with identification, nomenclature and classification of organisms is called taxonomy systematics

Term "Taxonomy" was given  by - > A.P. de Candolle

Father of Modern Taxonomy - > Carolus Linnaeusor .

Importance of classification :

The bewildering variety of life around us has evolved on earth. In order to make relevant groups to study, variety of life forms, we classify organism.

Classification makes the study of different type of organisms easy and systematic.

From classifiction, we can know all life forms together and as a whole.

Classification reveals the inter-relationship among organisms.

It helps in understanding the other branches of life sciences.

Hierarchy :- Hierachy is a system of classification into which taxonomic categories are arranged in descending order.

Category :- Plants and animals are ranked in an arrangement of known categories. Such as Kingdom, Phylum (for animals) or Division (for plants), Class, Order, Family, Genus and Species.

Taxon :- Taxon is defined as a unit of classification of organisms which can be recognised to a definite category at any level of classification e.g. fishes, insects etc.

Kingdom → Largest Group

Phylum (for animals) / Division (for plants)





                        Species → Lowest group




Classification and Evolution

Charles Darwin first described the idea of evolution in 1859 in his book, "The Origin of Species".

Darwin suggested that organisms are related to each other by descent. They had common ancestors from which they gradually evolved into their present form.

The ancestral forms were simple and are called 'primitive' and primitive organisms have evolved into advanced orgamisms which are more complex.

This process of gradual change from simple life forms to complex life forms is called 'Evolution'.

Nomenclature : (The naming of organisms)

Binomial Nomenclature : Binomial nomenclature was proposed by Carolus Linnaeus. According to his the name of any organism consists of two words.

The first word denoting the name of 'genus' and second word denoting 'species'.

First letter of generic name must be written in capital lettter whereas species name is started with small letter.

Scientific name is generally derived from Greek or Latin words.

The binomial names are printed in italics and underlined separately when written.


Examples :

Potato - Solanum tuberosum

Tiger - Panthera tigris


Do you know ?

Carolus Linnaeus proposed scientific name of plants in his book "Species Plantarum" (1753).
For animals' scientific name - "Systema Naturae" (1758).
Trinomial Nomenclature : Founder - Streekland
In this system, first name denoting - genus ; second to species and third to the subspecies.
e.g. Scientific name of 'crow' - Corvus splendens
Indian crow  - >  Corvus splendens splendens
Sri Lankan crow - >  Corvus splendens protegatus
[International Code of Biological Nomenclature] - Book of rules for nomenclature of organisms.
Artificial system : It based on habit, habitat and a few morphological characters.
e.g. Aristotle classified living organisms on the basis of habitat into water, land and air.
Theopharastus grouped plants on the basis of their habits into trees,shrubs, undershrubs and herbs.
Natural Systems : It based on natural affinities.
e.g. Bentham and Hooker's classification of seed plants.
Phylogenetic Systems :
Based on evolutionary relationships of organisms.
e.g. Engler and Prantl's classification of flowering plants.


Kingdom systems :

1. Two Kingdom Classification :

First suggested by Carolus Linnaeus in 1758.

Living organisms have been divided into two kingdoms.

Three Kingdom Classification:  Proposed by  Ernst Haeckel in 1886. He suggested a third Kingdom - Protista for unicellular organisms.
Four Kingdom Classification : Given by Copeland. He included Kingdom-Monera (Mychota) for prokaryotes.

(i) Kingdom Plantae - All the plants constitute kingdom planate. The kingdom includes bacteria, lichens, fungi, algae, bryophytes, ferns, gymnosperms and angiosperms.

(ii) Kingdom Animalia - All the animals constitute kingdom animalia. The kingdom animalia includes protozoans, sponges, Hydra, Jelly Fish, worms, insects, spiders, octopus, star fish, fishes, frogs, salamanders, lizards, snakes, birds and mammals.


Drawbacks in two kingdom classification :-

Certain organisms did not strictly fit either under plant or animal kingdom like :Euglena and Viruses.


Five kingdom classification :

This concept was propounded by Robert H. Whittaker in 1969.

On the basis of cell structure, complexity in organisms and type of nutrition, he divided living organisms into 5 kingdoms.(i) Monera, (ii) Protista, (iii) Fungi, (iv) Plantae, (v) Animalia.




Carl Woese (1977, 1994) has divided the kingdom monera into archaebacteria (= archea) and eubacteria (or bacteria). All other kingdom are included in his superkingdom of eukarya.

Characteristic of five kingdoms

1. Kingdom - Monera :

Prokaryotic Nature : The genetic material is not organised into a nucleus. It lies directly inside the cytoplasm and is called nucleoid.

Membrane Bound Cell Organelles. Membrane bound

cell organelles like mitochondria, Golgi apparatus, plastids, lysosomes, are absent.

Unicellular Nature : Monerans are basically unicellular.

In filaments and colonies the cells are similar and independent.

Mode of nutrition is either autotrophic (Blue-green algae) or heterotrophic(Mycoplasma and most bacteria).

Some organisms have cell wall (in bacteria) while other lacking (in Mycoplasma)




Examples :

Blue Green Algae (Cyanobacteria) Anabaena, Nostoc.

Bacteria (Vibrio cholerae, Clostridium botulinum, Escherichia coli)

Mycoplasma (Produces diseases in humans, animals and plants).

2. Kingdom - Protista :

Organisms are unicellulareukaryotic organization.

There is a true nucleus and membrane bound other cell organelles.

Cell wall : Some protists are covered with cell wall (most photosynthetic protists) while others do not possess it (e.g., protozoan protists).

Mode of nutrition is either autotrophic (algae and diatomes) or heterotrophic(protozoans).

Some organisms have cilia (e.g. Paramecium) ; flagellum (e.g. Euglena) andpseudopodia (e.g. Amoeba) for locomation.

Sexual reporduction is present but an embryo stage is absent.




Examples : Unicellular algae ChlamydomonasChlorella

Diatoms PinnulariaNavicula

Dinoflagellates Gonyaulax, Noctiluca

Protozoa Amoeba, Plasmodium, Euglena, Paramecium



Photosynthetic nutrition occurs in unicellular algae (e.g., dinoflagellates, diatoms) and  Euglena like organisms. They are the major producers of aquatic systems.
Holozoic nutrition is animal like nutrition where solid food particles are ingested. It is found in protozoan protists.
In absorptive nutrition, liquefied digested food is absorbed. It occurs in parasites and saprophytes.

Euglena and its relatives perform photosynthesis in light. In dark and in the presence of organic matter, they switch over to saprophytic nutrition. Such a dual nutrition is called mixotrophic nutrition.
Organisms with mixotrophic nutrition are called plant-animals.

3. Kingdom - Fungi

These are non-green (lacking chlorophyll)eukaryotic, organisms.

They may be unicelluar (e.g. Yeast) or Multicellular (most fungi).

The body of a multicellular and filamentous fungus is called mycelium and is composed of several thread like structures termed as hyphae.

Heterotrophic mode of nutrition is found.


Fungi are heterotrophic with absorptive nutrition. Most of them are decomposers (hence kingdom of
multicellular decomposers) or saprophytes which feed on organic remains by first secreting digestive enzymes and then absorbing the digested materials. A few fungi are also parasitic. Fungi show progressive reduction in sexuality. An embryo stage is absent.

Food is gained by either saprophytically (from dead organic matter) or parasitically (from other living tissues).

Cell Wall contain - Chitin.

Reserve food material - Glycogen.

Examples : Yeast, Rhizopus (Bread mould), PenicilliumMucor, Mushroom (Agaricus) ; Smut (Ustilago).


4. Kingdom - Plantae

Plants are multicellular, eukaryotes with cellulosic cell wall.

They are autotrophs i.e. prepare own food by photosynthesis.

5. Kingdom - Animalia

Animals are multicellular, eukaryotes without Cell Walls.

They are heterotrophic.

                                                                          Kingdom - Plantae


Characteristics : Plantae includes multicellular, eukaryote organisms with cellulosic with cell wall.

A mature plant cell commonly possess a single large central vacuole.

Plastids are found in all plants. Some plastids posses photosynthesis pigment. They are called chloroplasts.

Plants are autotrophic in nature because they are able to perform photosynthesis with the help of chlorophyll present in chloroplasts.

Reserve food is starch.

Do you know ?

Eichler (1883) divided the kingdom plantae into two subkingdoms, cryptogamae and phanerogamae.
Subkingdom : Cryptogamae (Gk. cryptos – hidden, gamous – marriage). The reproductive organs are inconspicuous. Flowers and seeds are absent. The embryo, if present is naked. Plants of subkingdom cryptogamae are also called lower plants, flowerless and seedless plants. There are three divisions in this subkingdom – Thallphyta, Bryophyta, Pteridophyta.
Subkingdom Phanerogamae (Gk. phaneros – visible, gamous – marriage). The plant which possess visible and well differentiated reproductive organs are called phanerogams. The plants of subkingdom phanerogamae have well differentiated and evident reproductive organs like seeds. Therefore, they are also called seed plants. Phanerogamae has single division of spermatophyta.


  Cryptogamae Phanaerogamae
1 It contains seedless plants. It contain seed plants.
2 It has both vascular and nonvascular p lants. It possesses only vascular plants.
3 An external water is required for fertilization. An external water is not required.

Bases of Classification

On the basis of differentiation of plant body.

On the basis of conducting tissue.

On the basis of ability to bear seeds and seed are enclosed within fruits.

Following plant groups are included in kingdom-Plantae


1. Thallophyta

Main plant body is gametophyte.

Plant body is not differentiated into root, stem and leaves, called thallus.

These are found in marine, fresh water and moist land.

They have not mechanical and conducting tissue.

Asexual reproduction generally take place by spores.

Sex organs are simple single-celled, (the male sex organs are called as antheridia and female sex organ called oogonia) and their is no embryo formation after fertilization.



Examples :

Green algae - Spirogyra, Ulothrix, Cladophora, Chara, Ulva, Chlorella

Brown algae - Laminaria, Fucus, Sargassum.

Red Algae - Polysiphonia



  Algae Fungi
1 Photosynthetic pigments are present. Photosynthetic pigments are absent.
2 Algae are autotrophic. Fungi are heterotrophic.
3 Most of the algae are aquatic. Most of the fungi are terrestrial.
4 The cell wall is made of cellulose. The cell wall is made of chitin.
5 Algae contain starch as a stored food material. l Fungi contain glycogen and oil as a stored food material.

2. Bryophyta

Bryophytes are also known as amphibians of plant kingdom.

These are the simplest and the most primitive land plant.

They have flat plant body which differentiate in to stem and leaf like structure.

Main plant body is gametophyte which attach to substratum by means of rhizoids.

Sex organs are multicellular and jacketed. Male sex organs are called antheridia while female sex organs are called archegonia.


Examples :

Liver wort - Riccia and Marchantia

Horn wort - Anthoceros

Moss - Funaria



3. Pteridophyta -

Main plant body is sporophyte which is differentiated into root, stem and leaves.

Vascular tissues, xylem and phloem, appear for the first time in pteridophyta.

They produces spores inside sporangia.

Gametophyte is a small but independent stage in life cycle.

Sex Organs are multicellular and jecketed like those of bryophytes male antheridia, female archegonia.

Male gametes need water for fertilization.

Seeds are absent.


Examples :

Club moss - Selaginella, Lycopodium

Horse tails - Equisetum

Ferns - Marsilea, Azolla, Adiantum,

Dryopteris, Pteris and Pteridium.


Spermatophyta (Gk. sperma seed, phyton plant)

Characteristics : Main plant body is a sporophyte which is differentiated into stem, leaves and roots.

Vascular tissues are well-developed throughout the plant body.

Sporangia occur over modified leaves called sporophylls. Sporophylls are aggregated to form cones or flowers.

Male and female gametophytes are distinct. They are small and dependent on the sporophyte for their nutrition.

Male gametophytes or pollen grains reach near the female sex organs through an external agency of wind, water or animals. The process is called pollination. Fertilization occurs with the help of a pollen tube. An external water is not required.

After fertilization plants produce seeds which contains embryo along with stored food. On germination each seed forms a new plant.

Spermatophyta or phanerogams are classified into two groups (Gymnosperm, Angiosperm) on the basis of naked or enclosed seeds.




4. Gymnosperm : 

Gymno- naked and sperm - seeds.

Plants are evergreen, woody and perennial. They are trees and shrubs.

Sporophylls are aggregated to form cones. There are separate male and female cones.

They bear naked seed. The seeds are not enclosed inside fruits. Instead they lie exposed over the megasporophylls.

Xylem lack vessels and phloem lack companion cells in Gymnosperm.


Examples :

Cycadae - Cycas

Coniferae - Pinus (Pines), Cedrus (deodar),Ginkgo.


5. Angiosperm -

 Angio- covered and sperm - seed.

Characteristics : Plants are deciduous or evergreen, annual

biennial or perennial herbs, shrubs or trees.

These are called flowering plant. Sporophylls are aggregated to form flowers. Flowers may be unisexual or bisexual.

Pollination occurs by wind, water and animals.

The plants of this group produce seeds inside an organ called ovary, which is modified in to fruit.

Endosperm is a new food storing structure which is generally triploid and is formed by fusion of three nuclei (triple fusion).

Embryo is present in the seed and bear leafy or fleshy structures called cotyledons (seed leaves)

Cotyledons represent a bit of pre-designed plant in the seed.


In angiosperms, a seed may have one or two cotyledons. On the basis of cotyledon number, angiosperms have been divided into two classes, dicotyledoneae and monocotyledoneae.


Class Dicotyledoneae :

It is a class of angiosperms in which seeds possess tow cotyledons. The plants of this class are commonly called dicots or dicotyledonous plants. Some other characters are reticulate venation, tap root system, pentamerous or tetramerous flowers. eg. Gram, Pea, Mustard, Ipomoea.


Class Monocotyledoneae :

The members of class monocotyledoneae of angiosperms are characterised by the occurrence of a single cotyledon in their seeds. They are commonly called monocots or monocotyledonous plants. Other characters of monocots are parallel venation, fibrous root system, trimerous flowers. eg. Lily, Coconut, Wheat, Maize, Grass, Bamboo, Paphiopedilum.



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