The cell is the basic structural and functional unit of all living organisms. Some organisms (like bacteria and amoeba) are made of a single cell, while others (like humans and plants) are made of many cells. Cells were first described by Robert Hooke in 1665.
Parts of a Cell and Their Functions
| Organelle | Function |
|---|---|
| Cell membrane | Controls movement of substances into and out of the cell (selectively permeable) |
| Cell wall (plants only) | Provides support, strength and a fixed shape; made of cellulose |
| Nucleus | Controls all cell activities; contains genetic material (DNA) |
| Cytoplasm | Site of many chemical reactions; holds organelles in place |
| Mitochondria | Site of aerobic respiration; releases energy (“powerhouse” of the cell) |
| Chloroplast (plants only) | Contains chlorophyll; site of photosynthesis |
| Vacuole | Stores cell sap; large and permanent in plant cells, small and temporary in animal cells |
| Ribosomes | Site of protein synthesis |
Differences Between Plant and Animal Cells
- Plant cells have a cell wall; animal cells do not.
- Plant cells contain chloroplasts for photosynthesis; animal cells do not.
- Plant cells have a large permanent vacuole; animal cells have small, temporary vacuoles.
- Plant cells are usually regular/rectangular in shape; animal cells are irregular/rounded.
Exam tip: When asked to draw a cell, always label the parts and use a sharp pencil with clear, thin lines. Marks are awarded for labels as well as the drawing.
Summary
The cell is the basic unit of life. Plant and animal cells share the nucleus, cytoplasm, cell membrane and mitochondria, but only plant cells have a cellulose cell wall, chloroplasts and a large vacuole. Knowing the function of each organelle is essential for WAEC.
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