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Basis of Classification: Levels of Organisation, Practice Problems and FAQs

Earth, the only planet with life, with millions of varieties of living forms. Just imagine how the situation would be if you need to count the characteristics of each and every creature on Earth individually! Tedious know?

To avoid this, it is extremely crucial to classify animals for better understanding of living species and the newly discovered species. Now the question arises! How to classify? 

We know that the thickness of a sheet and the length of a stick can’t be compared. We need to find out common parameters for comparison. Similarly, animals also have certain common characteristics which can actually form the basis of classification in distinguishing them. 

Let’s understand and analyse one of the most common bases of classification, i.e., levels of organisation. We will also peep inside the way in which levels of organisation help distinguishing organisms and creating groups out of them. 

different species of animals

Table of Contents:

Introduction to Levels of Organisation

The animal bodies are composed of cells which are arranged and grouped into different orders of complexities in different organisms. This is called the level of organisation.


Examples of Different Levels of Organisation

Digestive System

Different organs which are grouped together to perform digestion and absorption of nutrients form the digestive system. There are two types of digestive system:

  • Incomplete Digestive System

Digestive system that has only a single opening which performs functions of both the mouth and anus is called an incomplete digestive system. Example: Digestive system in Platyhelminthes.

open digestion system in flatworm

  • Complete Digestive System

Digestive system that has two different openings, one for ingestion (mouth) and the other for egestion (anus) is called a complete digestive system. Example: Digestive system in humans.

complete digestive system in humans

Circulatory System 

Group of organs that helps in the transport of blood and various metabolic products in an animal body constitute the circulatory system. There are two types of circulatory system:

  • Open circulatory System

In an open circulatory system, the blood flows through the sinuses and body cavities and the cells and tissues are directly bathed in the blood. Example: Circulatory system in arthropods.

open circulatory system in arthropods

  • Closed Circulatory System

In a closed circulatory system, the transport of blood occurs through blood vessels and capillaries. Example: Circulatory system in humans.

closed circulatory system in humans

Practice Problems of Basis of Classification

Question1. Heart and blood vessels in humans are a part of which organ system?

  • Digestive system
  • Circulatory system
  • Respiratory system
  • Organ system

Answer: In human beings, the heart primarily helps in pumping blood to various body parts through blood vessels. Hence, heart and blood vessels together form the circulatory system in humans.

Hence, the correct option is b.

Question2. Earthworms and humans are similar in having _________________ while snails are not.

Answer: Earthworms and humans belong to phylum Annelida and Chordata respectively. They are similar in having a closed circulatory system. Snails belong to phylum Mollusca which don’t have a closed circulatory system. 

Question3. Which of the following is commonly observed in lower phyla?

  • Incomplete digestive system
  • Complete digestive system
  • Closed circulatory system
  • Both b and c

Answer: Incomplete digestive system is the type of digestive system which is characterised by the presence of a single opening for both ingestion and egestion. It is observed in the members of the lower phyla like Coelenterata, Platyhelminthes.

Hence, the correct option is a.

Question4. A newly discovered organism, X, is composed of tissues, not organised into organs. It is likely to fall under which of the following phyla?

  • Coelenterata or Platyhelminthes
  • Coelenterata or Ctenophora
  • Porifera or Coelenterata 
  • Platyhelminthes or Aschelminthes

Answer: The level of organisation in which cells performing similar functions and having structural relatedness are grouped together to form tissues is termed the tissue level of body organisation. It is observed in the members of phylum Coelenterata and Ctenophora. Hence, the newly discovered organism, X, is likely to be a coelenterate or ctenophore.

Hence, the correct option is b.

FAQs of Basis of Classification

Question 1:- Incomplete digestive system is a feature of which phylum?

Answer: In an incomplete digestive system, there is only one opening, for both intake and elimination of food. That particular opening serves both as the mouth and anus. It is observed in flatworms that belong to Platyhelminthes.

Question 2:- Circulatory system is first observed in a complete state which of the following phylum?

Answer: In a closed circulatory system, the blood flows through closed blood vessels and a network of capillaries. The cells are not in direct contact with the blood. It is observed to be in a completed state in the members of phylum Annelida.

Question 3:- Define organ system level of body organisation?

Answer: The level of organisation in which organs, involved to achieve a particular function, form the organ system is termed as organ system level of body organisation. It is observed in the members of higher phyla from phylum Aschelminthes to Chordata.

Question 4:- Name the five levels of the organisation.

Answer: There are five levels of organisation which are as follows:

  • Cellular level of organisation
  • Tissue level of organisation
  • Organ level of organisation
  • Organ system level of organisation
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