AP Board Class 9 Biology Chapter 5 Diversity in Living Organisms

When we look at the world, we see a lot of diverse living organisms among us. However, we don’t know all the organisms that are present and it is quite impossible to know also as there are so many types and categories. However, in chapter 5 of AP board class 9 biology textbook students will study about the diversity present among several living organisms, learn how to classify them as well as understand terms like evolution and nomenclature.


Classification is defined as the systematic study of organisms that are present in nature. The main aim of classification is to help us easily explore the diversity of life forms and it also gives us an idea about evolution. There are several factors that need to be considered for classifying all organisms. They are:

i. Whether they are made of eukaryotic or prokaryotic cells.

ii. In terms of cell organization. Whether it is solitarily or in colonies (unicellular or multicellular).

iii. In terms of preparation of food (autotrophs or heterotrophs).

Classification system

The classification system has been changed a couple of times since its inception.

First, there was the two kingdom classification given by Carolus Linnaeus in 1758. He classified the living organisms into two groups namely animals and plants.

Then in 1959, the five-kingdom classification was established by H. Whittaker. He classified the living organisms into five kingdoms which are Kingdom Plantae, Kingdom Fungi, Kingdom Protista, Kingdom Monera, and kingdom Animalia.

However, in 1977, Carl Woese further divided kingdom Monera into Eubacteria (or Bacteria) and archaebacteria (or Archae).

Hierarchy of Classification

Plants and animals are basically ranked in an arrangement of known categories. These categories include;

  1. Kingdom
  2. Phylum(Animals) / Division(Plants)
  3. Class
  4. Order
  5. Family
  6. Genius
  7. Species

Diversity in Plants

Plants are usually classified under Kingdom Plantae (Plant Kingdom) and it is usually based on what kind of body structure they have or whether specialized tissues for transport is present or absent and finally whether the plant has the ability to bear seeds. Plants are divided into Thallophytes, Bryophyte, Pteridophyta, Gymnosperms and Angiosperms accordingly.

Diversity in Animals

Animals Kingdom are classified under Animalia and it consists of different phyla. The classification of animals is usually based on the characteristics of the organism like whether it is multicellular, eukaryotic, has a cell wall or heterotrophic. However, each phylum has organisms that have common characteristics but it usually shifts from the simplest to the most complex. The various classifications are Porifera or sponges, Coelenterata, Ctenophores, Platyhelminthes, Nematode, Mollusca, Annelida, Arthropoda, Echinodermata, Hemichordata, Chordata.


Nomenclature is the process of naming organisms with a distinctive scientific name. Nomenclature helps in providing a uniform way of identifying the vast diversity of life present in the world.

Question 1: What is Taxonomy and name the father of taxonomy.

Answer: Taxonomy is a subject that deals with the identification, nomenclature, and classification of organisms. The father of taxonomy is Carolus Linnaeus.

Question 2: Define Evolution.

Answer: Evolution is the process of acquiring change. During evolution, a new species is developed from an old species with gradual changes.

Question 3: Why do living organisms need to be classified into different categories?

Answer: The primary reason for classification of organisms is that it helps in better understanding of the specific organism that is to be studied. Further classification helps to study these organisms in a more systematic manner and in a much easy way. It also helps in focusing on the main aspects as well cover a large number of organisms.

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Practise This Question

Rahul was working on an experiment on the cells of onion peel. While observing the cells under the microscope, he finds many cells with thin thread like structures in their nucleus known as 'A'. In few other cells there were thick conspicuous X shaped structures called 'B' and in such cells he couldn't find the nuclear membrane. What is A and B?