Cells and Tissues

Cells and Tissues - Definition, Difference

Think about the different organisms we have read about. 

Now let us list a few;

• Amoeba
• Rose plant
• Cockroach
• Crow
• Dog
• Mango tree
• Elephant
• Human being

What is common between all these organisms?

They are all living

And what is a common factor in all living organisms?

They are composed of cells .

In organisms like Amoeba, Paramoecium , Euglena etc. a single cell is responsible for all the life supporting processes like respiration, digestion, movement, excretion etc.

They are single celled or unicellular organisms .

On the other hand, organisms like animals, plants and human beings are made of multiple cells and are multicellular organisms .

Millions of cells work are responsible for the life supporting processes in multicellular organisms

They are grouped to perform specialised functions

For example:

In animals - 

• Muscle cells contract and relax to cause movement
• Nerve cells carry messages
• Blood flows to transport oxygen, food, hormones and waste material

In plants-

• Vascular tissues conduct food and water from one part of the plant to other parts

Cells that are responsible for a particular function are grouped together.

A group of cells that are similar in structure and/or work together to achieve a particular function forms a tissue .

Example - Blood, Phloem, Muscles

This means, there is division of labour in multicellular organisms, as a group of cells called tissues are specialised for different activities .

So the levels of organisation in organisms are: