Cell – Structure and Functions
All living organisms on Earth are made up of tiny units called cells. The cell is the basic structural and functional unit of life. Just as a building is made of bricks, the bodies of living organisms are made up of cells.
1. Discovery of the Cell
In 1665, Robert Hooke observed a thin slice of cork under a microscope and discovered small box-like structures which he named cells.
Later, Antonie van Leeuwenhoek observed living cells in pond water using a powerful microscope and called them “animalcules”.
These discoveries led to the development of cell theory, which states that all living organisms are made of cells.
2. The Cell
A cell is the smallest unit of life capable of performing all essential functions for survival.
Examples of Cell Shapes- Nerve cells – long and branched
- Muscle cells – elongated
- Red blood cells – round and disc-shaped
3. Number of Cells in Organisms
Unicellular OrganismsThese organisms consist of a single cell performing all life processes.
- Amoeba
- Paramecium
- Bacteria
These organisms consist of many cells that work together.
- Humans
- Animals
- Plants
4. Shape and Size of Cells
Cells come in many shapes and sizes depending on their function.
- Nerve cells can be very long.
- Muscle cells are elongated.
- Plant cells are rectangular.
- Bacteria have some of the smallest cells.
5. Parts of a Cell
A typical cell has three main parts:
- Cell membrane
- Cytoplasm
- Nucleus
6. Cell Membrane
The cell membrane is the outer boundary of the cell that separates it from the environment.
Functions- Protects the cell
- Gives shape to the cell
- Controls movement of substances
It is semi-permeable, allowing some substances to pass through.
7. Cytoplasm
The cytoplasm is the jelly-like substance inside the cell membrane.
Functions- Holds organelles in place
- Supports chemical reactions
- Helps in cell metabolism
8. Nucleus
The nucleus is the control center of the cell.
Functions- Controls cell activities
- Regulates growth and reproduction
- Stores genetic information (DNA)
9. Plant Cells
Important Features- Cell Wall – provides strength and protection
- Vacuole – stores water and nutrients
- Chloroplast – contains chlorophyll for photosynthesis
10. Animal Cells
- No cell wall
- Smaller vacuoles
- No chloroplasts
- Usually round or irregular in shape
11. Comparison Between Plant and Animal Cells
- Plant cells have a cell wall, animal cells do not.
- Plant cells contain chloroplasts, animal cells do not.
- Plant cells have a large vacuole, animal cells have smaller ones.
12. Importance of Cells
- Provide structure to organisms
- Carry out metabolism
- Store genetic information
- Enable growth and development
- Allow reproduction
Conclusion
The cell is the fundamental unit of life and forms the building block of all living organisms. The discovery of cells by scientists such as Robert Hooke and Antonie van Leeuwenhoek revolutionized biology. Understanding cells helps us learn how organisms grow, function, and reproduce.