Cell structure and function
Cell structure and function is assessed through organelle recognition, structure-function links, and practical microscopy calculations. You must distinguish eukaryotic and prokaryotic cells, explain compartmentalisation, and use magnification and resolution correctly.
Organelles and compartmentalisation
- The nucleus stores DNA and controls transcription; mitochondria and chloroplasts have double membranes and their own DNA.
- Rough endoplasmic reticulum folds proteins; the Golgi modifies, sorts and packages them; lysosomes contain hydrolytic enzymes.
- Ribosomes are non-membrane-bound sites of translation; prokaryotic ribosomes are 70S, eukaryotic cytoplasmic ribosomes are 80S.
- Prokaryotes lack membrane-bound organelles and a true nucleus; their cell wall contains peptidoglycan.
Microscopy
Magnification = image size / actual size. Resolution is the smallest separation at which two points are distinct; electron microscopes have higher resolution than light microscopes because they use shorter wavelengths. A scale bar can be used to estimate actual size when magnification is unknown.
Worked example
An image of a cell is 40 mm long and the actual cell is 20 micrometres. Convert: 20 micrometres = 0.02 mm. Magnification = 40 / 0.02 = x2000. The reasoning depends on matching units before dividing.
Traps
Do not confuse magnification with resolution. Do not say all plant cells have chloroplasts. Ribosomes are not membrane-bound. A cell wall is not the same as a cell membrane.