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State the contributions made by Jansen, Hooke, Von Leeuwenhoek, Schleiden, Schwann, and Virchow
- Jansen - Invented compound microscope
- Hooke - Examines cork with improved compound microscope
- Von Leeuwenhoek - Observes unicellular organisms and nuclei
- Schleiden - Says all plants made of cells
- Schwann - Proposed cell theory with Schleiden. (All made of identical cells)
- Virchow - Omnis cellula e cellula
State three advantages of light microscopes
- Specimens can be alive
- Faster
- Cheaper
- Easier to maintain
- Smaller
- More colourful
State two advantages of electron microscopes
- Higher resolution
- Greater magnification
Define Organelle
A structure inside a cell that carries out a particular function.
Compare the relative sizes of cells, cell membrane thickness, viruses, bacteria, organelles , molecules, using appropriate SI units
- Molecules - 1 nm
- Membrane thickness - 10 nm
- Viruses - 100 nm
- Bacteria - 1 micrometre
- Organelles - 10 micrometres
- Cells - 100 micrometres
NB. 100 nm = 1 micrometre
Explain the importance of the surface area to volume ratio as a factor limiting cell size
- Rate of metabolism of a cell is a function of its mass/volume
- Rate of exchange of materials (nutrients and waste) and energy is a function of its surface area
- As a cell grows in size, the rate of chemical exchange with the extracellular environment might be inadequate to maintain cell as the cytoplasm is to far from the cell membrane.
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