Drawing Cells: Skills — IB Biology HL Revision Notes & Topical Questions

Question

• A drawn palisade cell is 60 mm long.
• The scale bar beside it is 20 mm long and represents 10 µm.
• Find the actual length of the cell and the magnification.

1. The scale bar shows that 20 mm on the page equals 10 µm in the specimen, so 2 mm equals 1 µm.
2. Actual length = 60 mm ÷ 2 mm per µm = 30 µm.
3. Convert the scale bar to the same unit: 20 mm = 20 000 µm.
4. Magnification = 20 000 ÷ 10 = 2000, and checking with the cell gives 60 000 µm ÷ 30 µm = 2000.

Answer

• Actual length 30 µm;
  • magnification ×2000

1.4.10 – Key Points for the Exam

• Biological drawing A labelled line diagram of observed specimens.
• Plan diagram An outline drawing showing the distribution of tissues without individual cells.
• Annotation A note added to a label that explains function or adaptation.
• Scale bar A line of known actual length drawn on a diagram or micrograph.

Common Mistakes

• Shading or colouring a drawing; use only clean outlines.
• Crossing label lines or adding arrowheads, which makes it unclear what is being labelled.
• Drawing individual cells in a plan diagram, which should show only tissue boundaries.
• Adding structures that should be present in theory but cannot actually be seen.