- Define and explain Using Microscopes in your own words
- Use key terms such as magnification accurately
- Apply what you have learned to new examples and questions
- Avoid the common mistakes learners make with this topic
This lesson focuses on Using Microscopes: learn how light microscopes work and practise calculating magnification.
Learn how light microscopes work and practise calculating magnification.
Key ideas
Microscopes and magnification
A light microscope uses light and glass lenses to magnify specimens up to about 1500 times. Electron microscopes reach far higher magnifications and resolution but cannot view living cells. Magnification is calculated with: magnification = image size ÷ real size. Always convert both measurements to the same units before dividing, for example millimetres to micrometres (1 mm = 1000 μm).
Specialised cells
Cells differentiate to suit their function. Root hair cells have long hairs that increase surface area for absorbing water. Sperm cells have a streamlined head, many mitochondria for energy, and a tail for swimming. Red blood cells have no nucleus, leaving maximum space for haemoglobin to carry oxygen, and a biconcave shape that increases surface area. A cell's structure always matches its job.
Key term — magnification: How many times larger an image appears compared with the real object, calculated as image size divided by real size.
A drawing of a cell measures 15 mm across. The drawing was made at ×100 magnification. What is the real width of the cell in micrometres?
Use the formula: real size = image size ÷ magnification. Divide: 15 mm ÷ 100 = 0.15 mm. Convert millimetres to micrometres: 0.15 × 1000 = 150 μm.
Answer: The cell is 150 μm wide.
- Confusing magnification with resolution Magnification makes things bigger; resolution makes them clearer. A blurry image magnified 1000 times is still blurry.
- Forgetting to convert units Image size and real size must be in the same units before dividing. Convert millimetres to micrometres first (multiply by 1000).
Practice
40 ÷ 200 = 0.2 mm.
Mitochondria release energy by respiration. The sperm needs large amounts of energy to swim towards the egg, so many mitochondria supply it.
Losing the nucleus leaves more space for haemoglobin, so each cell can carry as much oxygen as possible.
Any two of: growth (increasing cell number); repair of damaged tissue; replacement of worn-out cells.
Quick check
Which of these best defines "magnification"?
Why does a root hair cell have a long hair-like extension?
Oxygen moves from the air in the lungs into the blood. Explain why, using the term concentration gradient.
- Using Microscopes: learn how light microscopes work and practise calculating magnification.
- Microscopes and magnification: A light microscope uses light and glass lenses to magnify specimens up to about 1500 times.
- resolution: The ability to distinguish two separate points; a microscope with higher resolution gives a sharper, clearer image.
- Watch out for: confusing magnification with resolution