The cell: the unit of life
The cell is the basic unit of life. All living things are made of cells. Most cells are far too small to see without a microscope. Some organisms, like bacteria, are a single cell; a human has about 37 trillion.
| Part | Animal cell | Plant cell |
|---|---|---|
| Cell membrane | yes | yes |
| Nucleus | yes | yes |
| Cytoplasm | yes | yes |
| Mitochondria | yes | yes |
| Cell wall | no | yes |
| Chloroplasts | no | yes (in green parts) |
| Large permanent vacuole | no (small ones) | yes |
Using the microscope
A light microscope has two lenses that magnify. The total magnification is the eyepiece magnification multiplied by the objective magnification. Focus first with the low-power lens and the coarse-focus knob, then move to a stronger lens and use the fine-focus knob.
A cell is 0.05 mm across. Choose the lenses and see how large the image appears.
Focus on a specimen and practise the correct procedure. Label the parts of a cell
Drag each label to the right organelle.
From cells to organisms
Cells of the same kind form a tissue (for example muscle tissue). Different tissues form an organ (for example the heart). Organs working together form an organ system (for example the circulatory system) and the systems make up the whole organism.
Key terms
- Cell
- The basic unit of life.
- Organelle
- A part inside a cell with a particular job.
- Tissue
- A group of similar cells doing the same job.
- Organ
- A group of tissues working together.
Summary
- All living things are made of cells.
- Plant cells have a cell wall, chloroplasts and a large vacuole; animal cells do not.
- Total magnification = eyepiece × objective.
- Cells → tissues → organs → organ systems → organism.