Revision:Cell Theory 2

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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

1. Specimens can be alive
2. Faster
3. Cheaper
4. Easier to maintain
5. Smaller
6. More colourful

State two advantages of electron microscopes

1. Higher resolution
2. 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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