1.3 Unit of Life – Cells
In brief:The cell is the basic unit of life. All living things are made of one or more cells. Animal and plant cells share many organelles but have key differences.
The cell is the basic structural and functional unit of all living things. All cells arise from pre-existing cells (cell theory).
Cell Theory (Schleiden, Schwann, Virchow):
1. All living things are made of one or more cells
2. The cell is the basic unit of life
3. All cells arise from pre-existing cells
Microscopy:
• Light microscope: magnification up to ~1,500×. Can view living cells. Uses visible light and glass lenses.
• Electron microscope: magnification up to ~500,000×. Much higher resolution. Uses electron beams. Cannot view living cells (specimen must be dead and in a vacuum).
Key differences between plant and animal cells:
• Plant cells only: cell wall (cellulose), chloroplasts (photosynthesis), large central vacuole (turgor pressure)
• Animal cells only: centrioles (cell division), lysosomes (more prominent), small vacuoles
• Both have: cell membrane, cytoplasm, nucleus, mitochondria, ribosomes, ER, Golgi apparatus
Animal cell
Wikimedia Commons (public domain / CC)
Plant cell
Wikimedia Commons (public domain / CC)
Key Cell Organelles and Their Functions
Plant Cell vs Animal Cell
Plant Cell
- Cell wall (cellulose)
- Chloroplasts
- Large central vacuole
- Regular, fixed shape
- Starch for energy storage
Animal Cell
- No cell wall
- No chloroplasts
- Small vacuoles
- Irregular shape
- Glycogen for energy storage
- Centrioles present
Key Points
- 1Levels of organisation: cell → tissue → organ → organ system → organism.
- 2Light microscope: lower magnification, can view living cells.
- 3Electron microscope: much higher magnification and resolution, views fine detail of organelles.
- 4Plant cell only: cell wall, chloroplast, large central vacuole.
- 5Animal cell only: centrioles (in some), small vacuoles.
- 6Both: cell membrane, cytoplasm, nucleus, mitochondria, ribosomes, endoplasmic reticulum, Golgi apparatus.
Learning Outcomes
- Describe the complexity of multicellular organisms
- Compare the structure of prokaryotic and eukaryotic cells
- Investigate, using primary data gathered with a light microscope and secondary data gathered from scanning electron microscope imagery, the structures and organelles of animal and plant cells and relate them to their functions