Cells and Cell Biology
What you must understand
Every living thing is built from cells, and the cell is the smallest unit that can carry out all life processes. You need to know the shared features of all cells (cell membrane, cytoplasm, genetic material, ribosomes) and the differences between prokaryotic cells (bacteria: no nucleus, no membrane-bound organelles, circular DNA, often a cell wall and plasmids) and eukaryotic cells (plant, animal, fungal, protist: DNA enclosed in a nucleus, membrane-bound organelles).
Learn the functions of the main organelles: nucleus (controls activity, holds chromosomes), mitochondria (aerobic respiration releases energy), ribosomes (protein synthesis), rough and smooth endoplasmic reticulum (protein transport and lipid synthesis), Golgi apparatus (modifying and packaging proteins), lysosomes (digestion of worn parts), chloroplasts (photosynthesis), vacuole (storage and turgor), and cell wall (support, made of cellulose in plants, chitin in fungi, peptidoglycan in bacteria).
Traps examiners set
- Saying plant cells have "no mitochondria" - they have them; they simply also have chloroplasts.
- Confusing the cell wall (support, fully permeable) with the cell membrane (selective control of entry and exit).
- Calling a bacterial cell "simple" and then claiming it lacks ribosomes - it has them.
- Mixing up magnification and resolution; resolution is the ability to distinguish two close points.
Worked rule of thumb
Magnification = image size ÷ actual size. Always convert to the same units first: if a 0.05 mm object is drawn 10 mm wide, magnification = 10 ÷ 0.05 = ×200. Rearrange the same equation to find actual size when magnification is given.