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š¬ Think about it
A single brick can't make a house, but bricks build walls, walls build rooms, and rooms build a house. Living bodies are organised step by step too. What are these steps? Let's find out.
How is the body of a living organism organised?
How is a living body built up, level by level?
Cell
The basic unit of life
↓
Tissue
A group of similar cells
↓
Organ
Tissues doing a major job
↓
Organ System
Organs working together
↓
Organism (the whole living body)
- A cell is the basic unit of life.
- Similar cells form a tissue; tissues form an organ.
- Organs form an organ system; systems make a whole organism.
Can you give an example of these levels in the human body?
| Level | Example in the human body |
|---|---|
| Cell | Muscle cell |
| Tissue | Muscle tissue |
| Organ | Stomach |
| Organ system | Digestive system |
| Organism | The whole human being |
- Muscle cells join to form muscle tissue.
- Muscle tissue helps form an organ like the stomach.
- The stomach is part of the digestive system in the body.
What is a multicellular organism?
Is the body made of one cell or many?
Living organisms
One cell or many
Unicellular
Just one cell
Does every job alone
Example:
Bacteria
Amoeba
Protozoa
Yeast
Multicellular
Many cells, from one egg
Cells share the work
Example:
Humans
Animals
Plants
Mould
- It is a living being made of many cells.
- Its life begins from a single cell (the egg).
- That cell divides again and again to form the whole body.
Example:
Plants, animals, and humans are all multicellular organisms.
Important Points
- These levels show how simple cells build a complex living body.
- The life of a complex organism begins from one single cell, the egg.
š Ever heard of ...
- The yolk of an ostrich egg is a single cell.
- It is the largest known cell in the living world.
- It measures about 130–170 mm across.
Important Definitions
- Tissue — A group of similar cells working together.
- Organ — Different tissues organised to do a major job.
- Organ system — Several organs working together for a major function.
- Multicellular organism — A living being made up of many cells.
