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Getting started: cells and the light microscope
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Every living thing is made of cells. At KS3 you met animal and plant cells and used a microscope. GCSE builds straight on this, so let us make it solid.
Cells are the building blocks
All living things are made of cells. Some organisms are a single cell (unicellular); you are made of trillions (multicellular).
Animal and plant cells both have:
Nucleus: contains genetic material and controls the cell.
Cytoplasm: where most chemical reactions happen.
Cell membrane: controls what goes in and out.
Mitochondria: where aerobic respiration happens.
Animal and plant cells both have:
Nucleus: contains genetic material and controls the cell.
Cytoplasm: where most chemical reactions happen.
Cell membrane: controls what goes in and out.
Mitochondria: where aerobic respiration happens.
Extra parts in plant cells
Plant cells also have:
Cell wall: made of cellulose; supports the cell.
Chloroplasts: where photosynthesis happens.
Permanent vacuole: filled with cell sap; keeps the cell firm.
Cell wall: made of cellulose; supports the cell.
Chloroplasts: where photosynthesis happens.
Permanent vacuole: filled with cell sap; keeps the cell firm.
Using a light microscope
1. Put the slide on the stage. A stain (iodine for onion cells, methylene blue for cheek cells) makes parts such as the nucleus easier to see.
2. Start with the lowest-power objective lens: it shows a wider area, so the cells are easier to find.
3. Focus with the coarse focusing knob, then sharpen with the fine focusing knob. Then switch to a higher-power lens and refocus with the fine knob.
Total magnification = eyepiece lens magnification × objective lens magnification
2. Start with the lowest-power objective lens: it shows a wider area, so the cells are easier to find.
3. Focus with the coarse focusing knob, then sharpen with the fine focusing knob. Then switch to a higher-power lens and refocus with the fine knob.
Total magnification = eyepiece lens magnification × objective lens magnification
A student uses a ×10 eyepiece lens and a ×40 objective lens. What is the total magnification?
- Total magnification = eyepiece × objective
- = 10 × 40
Answer: ×400
Animal and plant cells share a nucleus, cytoplasm, cell membrane and mitochondria; plant cells add a cell wall, chloroplasts and a permanent vacuole. Total magnification = eyepiece × objective.
The interactive lesson includes the diagrams for this topic.
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