Eukaryotic cells, found in animals, plants, fungi and protists, have their genetic material enclosed in a nucleus. Prokaryotic cells, such as bacteria, are much smaller and have no nucleus: their DNA is a single loop in the cytoplasm, often with extra small rings called plasmids. Both have cell membranes, cytoplasm and ribosomes, where proteins are made.
Light microscopes magnify up to about ×2000; electron microscopes have a much higher resolution, so they reveal small structures like ribosomes and the inside of mitochondria. Magnification = image size ÷ real size. Units must match: 1 mm = 1000 µm. Cell sizes are often written in standard form, for example a bacterium is about 1 × 10⁻⁶ m long.
Worked example
A cell image is 5 mm long and the real cell is 50 µm. What is the magnification?
- Convert to the same units: 5 mm = 5000 µm.
- Magnification = image ÷ real = 5000 ÷ 50.
Answer:The magnification is ×100.
Key words
- eukaryotic
- cell with a nucleus
- prokaryotic
- cell without a nucleus, e.g. bacteria
- plasmid
- small ring of DNA in bacteria
- resolution
- the ability to tell two close points apart
New questions every time.
NGSS-referenced: HS-LS1-1