Basic Unit of Organism

 Key Concepts

• Living cell
• Unicellular
• Multicellular

Introduction

Living things are organisms that have a life and can grow, respire, require food to get energy, and die. Humans, plants, animals, and microorganisms are living organisms. Non-living things do not have a life span. They do not respire as they do not require food for energy. Water, soil, air are examples of non-living things. 

Living organisms 

Non-living organisms 

All living organisms, whether plants, animals, or microorganisms, are made up of a basic unit called a cell. The cell is the smallest unit of living things that can carry out the basic processes of life. The tiny bacteria and the large blue whale are made of cells. We cannot see the cells with our naked eyes.

Scientists use microscopes that enlarge objects. Stains (dyes) are used to color parts of the cell to study the structure. In 1665, Robert Hooke first discovered and observed the cell. All living organisms differ in shape and size because they vary in size, shape, and number of cells in their body. The egg of a hen represents a single cell and is big enough to be seen by the naked eye, and we do not need a microscope to observe it. 

Classification of organisms  

The number of cells is billions and trillions. The human body has trillions of cells that differ in shape and size. The organism can be of 2 types based on the number of cells in its body.  

Organisms made of more than one cell in which each cell is specific for certain functions are called multicellular organisms. 

Some organisms’ bodies are made up of only a single cell and can carry out all life processes are known as unicellular organisms.  

Example: Microorganisms like an Amoeba, yeast, plasmodium, paramecium, E. coli, euglena. 

Unicellular organisms 

The shape of the cell 

The shape of the cells is different in living organisms. For example, animal cells are usually round, while plant cells are rectangular in shape. Bacteria like E. coli are rod-like, and nerve cells are long and branched.

 

Size and functions of cell  

The size of the cell is not related to the size of the body of the animal or plant. The size of the cell is concerned with its function. For example, nerve cells, both in the whale and mouse, are long and branched. They perform the same function, that of the transfer of messages. ‘Red blood cells- to transfer gases. White blood cells- to protect against diseases. Guard cells- to open and close stomata in plants. Sperm cells- to transfer genetic material. Muscle cells- to show movement.’ 

Summary

• The cell is the smallest unit of living things that can carry out the basic processes of life.
• Robert Hooke first discovered and observed the cell in 1665.
• Scientists use microscopes that enlarge objects. Stains (dyes) are used to color parts of the cell to study the structure.
• Organisms made of more than one cell and each cell-specific for certain functions are called multicellular organisms.
• Some organisms’ bodies are made up of only a single cell and can carry out all life processes; these are known as unicellular organisms.
• The size of the cells is not related to the size of the body of the animal or plant.
• The size of the cell is not related to the size of the body of the animal or plant. The size of the cell is concerned with it’s function.