Lesson overview
Cells under the microscope: What does a microscope reveal inside a cell?
Peel the skin of an onion, stain it and lower a coverslip. Focus the microscope from low to high power, compare cheek cells and a pondweed leaf, then measure one onion cell.
Suggested sequence
- Lesson 1 · Plant and animal cells. Plant, animal and bacterial cells: what a microscope shows and what each structure does. Read together (10–15 min), show or explore the experiment (10 min), practise with self-checking (15–20 min).
- Lesson 2 · Specialised cells and organisation. New cells from cell division, specialised cells and the levels from cell to organism. Read together and discuss (15–20 min), practise with self-checking (20–25 min).
- Lesson 3 · Magnification. Magnification and actual size, in millimetres and micrometres. Read together (10–15 min), show or explore the experiment (10 min), practise with self-checking (15–20 min).
- End of module · final check. 4 new questions, 20–30 min, without hints or notes; pupils check their answers once they have answered them all.
- One to two weeks later · return questions. 5 questions, 15 min, lesson closed.
Learning goals
Part 1: Plant and animal cells
- Describe and compare the structure of a plant cell and an animal cell (2.1.1)
- Describe the structure of a bacterial cell (2.1.2)
- Identify cell structures in diagrams and images of plant, animal and bacterial cells (2.1.3)
- Describe the functions of the structures in plant, animal and bacterial cells (2.1.4)
Part 2: Specialised cells and organisation
- State that new cells are produced by division of existing cells (2.1.5)
- State the functions of specialised cells and relate their features to them (2.1.6)
- Describe the levels of organisation: cell, tissue, organ, organ system, organism (2.1.7)
Part 3: Magnification
- State and use the formula magnification = image size ÷ actual size; calculate magnification and actual size using millimetres (2.2.1, 2.2.2)
- Calculate sizes and magnification with millimetres and micrometres, converting between the two units (2.2.3)
Misconceptions to listen for
- “The cell wall controls what enters the cell.” — The cellulose wall is like a strong net: water and dissolved substances pass through it. The thin membrane inside it is the layer that controls entry and exit.
- “The nucleus decides what enters the cell.” — The nucleus controls the cell’s activities through its DNA, but substances actually cross the cell membrane.
- “Mitochondria make energy.” — Energy cannot be made. Aerobic respiration in the mitochondria releases energy that was stored in food.
- “Chloroplasts are in every cell.” — Only plant cells in green parts have chloroplasts; onion skin and root cells have none, and animal cells never do.
- “The circular DNA is the bacterium’s nucleus.” — A bacterium has no nucleus: its DNA lies loose in the cytoplasm as one loop.
- “Plasmids are where a bacterium makes proteins.” — Proteins are made on ribosomes. Plasmids are small rings of DNA that carry a few extra genes.
- “The outline of each cheek cell is a cell wall.” — Animal cells have no wall. The outline you see is the cell membrane, the thin layer round every cell.
- “An animal cell has no membrane, because you cannot see a wall.” — Every cell has a membrane. In a cheek cell it is the outline itself; in a plant cell it is pressed against the inside of the wall.
- “Animal cells have no membrane, because they have no wall.” — Every cell has a membrane. A plant cell has a wall as well, outside its membrane.
- “Animal cells have no nucleus.” — Nearly all animal cells have a nucleus; your cheek cells each had one. (Red blood cells are a special exception.)
Scope
The structure and functions of plant, animal and bacterial cells (2.1.1–2.1.4) through a microscope practical: preparing an onion-skin slide, focusing from low to high power, and comparing cheek cells and a pondweed leaf. Part 2 covers cell division, specialised cells and levels of organisation (2.1.5–2.1.7); part 3 magnification and units (2.2.1–2.2.3).