Diversity in the living world class 11 is the first unit in biology syllabus. It is an important chapter weightage wise. In this chapter, you will learn about the diverse living organisms that inhabit the Earth from Taxonomy perspective. You will have an in-depth understanding of the classification, properties, attributes and exceptional features of living organisms. Moreover, the concepts learned from this chapter will help to give an insight into further chapters in biology. Therefore, it is important to comprehend the concepts and theories of this chapter.
What is Diversity in the Living World?
The world is dominated by a plethora of living organisms living in the land, water, ice, desserts, etc. Every living organism is unique with respect to structure, body functions, genetic make-up and so on. The living organisms found in different habitats have different structural organs or functions developed as per the conditions of their habitat. Organisms have evolved to adapt to their changing environments. Different types and classes of organisms inhabiting different environments is known as biodiversity. Regions that are warm and humid have more diverse organisms and are called mega-biodiversity.
Humans have evolved from apes. But now they don’t look similar in any way. Also, every individual is different from the other. Every individual has a different skin colour, hair colour, eyes, and most important of all is the genetic makeup. Which means, genes of every individual are different.
Thus, to identify better, we have created groups of organisms that somehow look similar and have some functional and structural similarities. This is known as classification. There are various factors that influence the classification of organisms. It is majorly carried out on the basis of the following criteria -
Presence of nucleus
Body design which implies the make-up of cells or the presence of single or multiple cells
Level of the organization in bodies of organisms carrying out photosynthesis
In animals – an organization of one’s body parts, development of body, specialized organs for different functions, organs systems.
The classification of organisms is done by two methods. One is classifying them into plants and animals and the other one which is a five-kingdom system is a more detailed and organized classification of organisms:
Two - Kingdom Classification - The two-kingdom classification system was proposed by Carolus Linnaeus. He classified organisms into two categories- plants and animals.
Five - Kingdom Classification - This broad and organized classification system was proposed by Whittaker. He divided the organisms into five different classes that are -
Hierarchy of Classification
Carolus Linnaeus also arranged the organisms into different taxonomic groups at different levels. These taxonomic groups in a serial order are as follows -
Characteristics of Five Kingdoms
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These are unicellular prokaryotes.
The organisms lack a true nucleus.
They may or may not contain a cell wall.
They may be heterotrophic or autotrophic in nature.
For example- Bacteria, Cyanobacteria
Unicellular and eukaryotic organisms come under this group.
They exhibit an autotrophic or heterotrophic mode of nutrition.
They show the presence of pseudopodia, cilia, or flagella for locomotion.
For example- amoeba, paramecium
These are multicellular, eukaryotic organisms.
They possess a saprophytic mode of nutrition which involves chemoheterotrophic extracellular digestion.
The cell wall in these organisms is made up of chitin.
They live in a symbiotic relationship with blue-green algae.
For example- Yeast, Aspergillus
These are multicellular, eukaryotic organisms.
The cell wall of these organisms is made up of cellulose.
They are heterotrophs and prepare their own food by means of photosynthesis.
Kingdom Plantae is subdivided into- Thallophyta, Bryophyta, Pteridophyta, Gymnosperms, Angiosperms.
For example- Pines, ferns, palm tree, mango tree, etc.
These are multicellular, eukaryotic organisms but they do not show the presence of cell walls.
They are heterotrophs or organisms who cannot prepare their own food.
Both simple and complex organisms are seen in this group and it’s a very broad group of organisms.
The organisms are genetically diverse.
They exhibit an organ-system level of organization.
It is subdivided into different phyla such as Porifera, Coelenterata, Echinodermata, Chordata, Annelids, etc.
For example- Earthworms, Hydra, etc.
1. What is Evolution? How is it Connected to the Classification of Organisms?
Life on Earth started billions of years ago. Smaller and simpler life emerged first and as the environmental changes occurred, simple organisms developed complex functions and changed into complex organisms to survive with the changing climate. This is known as evolution. Charles Darwin better explained the phenomenon of the emergence of life and its evolution in his works and writings. He has also put forward theories on how life emerged and the basis of continuity of life, the concept of survival of fittest, and so on.
Evolution is connected to classification because of two major inferences drawn from the theory of evolutions-
Lower organisms are the one who has not changed over a period of time and they continue to survive with their basic and primitive body structures.
Higher organisms are relatively recent and have developed complex body functions to survive and reproduce and produce more healthy progenies to continue their race.
2. What is the Two-kingdom Classification? What are its Limitations?
Two kingdom classification was given by Carolus Linnaeus. He classified organisms into two categories- plants and animals.
The limitations of two-kingdom classification are as follows-
As per this classification system, organisms are either plants or animals. But primitive organisms that evolved first were neither of the two.
Fungi is a different class of organisms with different structure, physiology and way of reproduction.
The classification fails to divide lower organisms into either of the groups.
Class of decomposers is not well defined as per this system