Cell KS3
What is a Cell?
A cell is the smallest unit of life. All living things (plants, animals, fungi, bacteria) are made of cells.
Some organisms are just one cell (like bacteria). Others, like humans, are made of trillions of cells!
How Do We See Cells?
We use a light microscope to view cells.
Microscopes magnify tiny things, allowing us to:
- Observe the cell shape
- Identify parts (organelles) inside the cell
- Draw and label what we see
Main Parts of a Cell & Their Functions
| Organelle | Function |
|---|---|
| Cell membrane | Controls what enters and leaves the cell |
| Cytoplasm | Jelly-like fluid where chemical reactions happen |
| Nucleus | Contains DNA and controls the cell |
| Mitochondria | Where respiration happens (energy is released) |
| Vacuole | Stores water and nutrients (mainly in plant cells) |
| Cell wall | Gives structure and strength to plant cells |
| Chloroplasts | Absorb sunlight for photosynthesis in plant cells |
Plant vs Animal Cells
Diffusion
Diffusion is when particles move from an area of high concentration to low concentration.
For example:
- Oxygen diffuses into cells
- Carbon dioxide diffuses out of cells
Unicellular Organisms
These are organisms made of one single cell.
Examples:
- Amoeba – changes shape to move and catch food
- Euglena – uses sunlight (like plants) but can move (like animals)
They have special structures to survive, such as flagella (tails), cilia (tiny hairs), or vacuoles.
Levels of Organisation in Living Things
Living organisms are organised like this:
Cells → Tissues → Organs → Organ Systems → Organism
Example in humans:
- Muscle cell → Muscle tissue → Heart (organ) → Circulatory system → Human