Class 9 Biology Notes – Chapter Number 3  BIODIVERSITY

Class 9 Biology Notes – Chapter Number 3  BIODIVERSITY


Question#1) Define Biodiversity?

Answer: Biodiversity: The term “biodiversity” has been derived from ‘bio’ and ‘diversity’.  Biodiversity is a measure of the variety of organisms present in different ecosystems or earth surface.

Flora: Diversity of plants in an ecosystem is called flora.

Fauna: Diversity of animals in an ecosystem is called flora.

Question#2) How many kinds of Organisms inhabiting the earth nowadays?

Answer: At least 10 million kinds of organisms inhabit the Earth but less than one third of these have been studied and cataloged (put in record) by biologists.

Question#3) Write a note on Origin of life?

Answer: The origin of life is not well known to science, though limited evidence suggests that until 600 million years ago, all life consisted of bacteria and similar unicellular organisms.

Question#4)Relate the Importance of biodiversity with natural ecosystem through examples.

Answer: Importance of Biodiversity: Biodiversity provides food for humans for example some vegetable plants, fruits, etc. A significant proportion of drugs are derived, directly or indirectly, from biological sources. For example some anti-cancerous drugs are obtained from Taxus bacata . A wide range of industrial materials e.g. building materials, fibers, dyes, resins, gums, adhesives, rubber and oil are derived directly from plants.

Biodiversity plays important role in making and maintaining ecosystems. It plays a part in regulating the chemistry of our atmosphere and water supply. Biodiversity is directly involved in recycling nutrients and providing fertile soils.

Question#5) Define Taxonomy and Classification? How are taxonomy and systematic related?

Answer: Taxonomy: The branch of biology deals with the identification, nomenclature and classification of living organisms is called taxonomy.

Classification: The arrangement of organisms into groups and sub groups on the basis of similarities is called classification.

Systematics: The branch of biology that deals with classification and also traces the evolutionary history of organisms is known as systematics.

Question#6) Explain the aims, principles and need of biological classification keeping in view its historical background?

Answer: Need and importance of Biological classification keeping in view its historical background: There is a large collection of very dissimilar forms of organisms, found on Earth. Over 1.5 million types of animals and over 0.5 million types of plants are known to biologists and these are only a small percentage of the total types estimated to live on Earth. They range in complexity from small and simple bacteria to large and complex human beings. Some of them live in sea, some on land; some walk, others fly, and still others are stationary. Each has its own way of life i.e. getting food, avoiding unfavorable environmental conditions, finding a place to live, and reproducing its kind. When there are so many diverse kinds of organisms, it becomes difficult to learn about the characteristics of each.

To study such a large collection, biologists classify the organisms into groups and subgroups and for this task they require some system. Biological classification is a method by which biologists divide organisms into groups and subgroups.

Aims and Objectives: –

The aims and objectives of classification are as under: –

  1. i) Determine similarities and differences between organismsso that they can be studied easily.
  2. ii) Arrange organisms according to similarities and differences.

iii) Identify the organisms on the basis of structure and prominent features.

  1. iv) Finds out inter relationship of organisms.
  2. V) To find the evolutionary relationships among organisms.

Basis and Principles of Classification
The classification of organisms is based on such features or characters, which are similar in one kind of organisms and different in different kind of organisms. These characters may be about internal morphology, (anatomy), external morphology, physiology, cell structure, especially the number of chromosomes and chemical composition (especially of proteins) and embryology of the organisms. These characters help in study of intra specific (within the same species) and intra specific (between different) species differences. The presence of similar characters in different organisms indicates their common ancestry. This similarity because of common ancestral origin is called Homology e.g. arm of a monkey, flipper of a whale and wing of a bat show homology. They are dissimilar apparently but their internal structure (arrangement of bones and muscles) is same. These organs are called homologous organs. Due to this homology, we can, say that monkey, whale and bad had common ancestors and are placed in same large group “vertebrate”. This homology is proved to be very helpful in classification.


Question#7) what is meant by taxonomic hierarchy? Also write a comprehensive note on species (basic unit of classification).

Answer:Taxonomic Hierarchy: The groups into which organisms are classified are known as taxonomic categories or taxa (singular “taxon”).   “OR”  Any group in the taxonomic categories or taxanomic classification is termed as taxon. A ladder like structure formed by taxanomic categories is known as Taxanomic hierarchy. All organisms are divided into five kingdoms. So kingdom is the largest taxon. On the basis of similarities, each kingdom is further divided into smaller taxa in the following way:



  • Phylum (Division: for plants and fungi):A phylum is a group of related classes.
  • Class:A class is a group of related orders.
  • Order:An order is a group of related families.
  • Family:A family is a group of related genera.
  • Genus:A genus is a group of related species.
  • Species:A species consists of similar organisms.


Members of lower taxon resemble one another more than the members of a higher taxon. Table below illustrates the classifications of humans (Homo sapiens) and pea (Pisum sativum).


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