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1.3.10Additional lessons

Drawing Cells- Skills — IB Biology SL Revision Notes & Topical Questions

5 min read 6 parts Lesson 4 of 142

📚 IB Biology SL Hub / Topical Revision
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Part 1 of 6Purpose of a Drawing

1.3.10 Drawing Cells- Skills
Purpose of a Drawing
Record
  • A drawing records what was seen, so that observations can be checked later when the specimen is no longer available.
Selection
  • Only the clear and important features are drawn, which helps focus on the structures that matter.
Honesty
  • Draw only what you see, not what you think should be there, because a drawing is evidence.
Cell drawing
  • A cell drawing shows individual cells at high power, while a plan diagram shows tissue layers at low power.

Part 2 of 6Drawing Conventions

Materials
  • Use a sharp HB pencil and a good eraser on plain white paper.
Lines
  • Use clear, continuous single lines with no sketching or shading, and make proportions accurate.
Size
  • The drawing should fill much of the available space so that fine detail can be shown clearly.
Title
  • Give the drawing a title, and state the magnification at which the observations were made.
Scale bar
  • A line of known actual length can be added to show the scale of the drawing.

Part 3 of 6Labelling

1
Draw each label line with a ruler so that it is straight, and make it touch the structure being named.
2
Keep label lines from crossing each other, and do not use arrowheads on them.
3
Place the labels in a neat column at the side of the drawing, level with the top of the page.
4
Add short annotations that state the function of key organelles or the cell as a whole.
5
Check that the title, magnification and all labels are present before finishing.

Part 4 of 6Cells and Plans

Cells and Plans
High power drawing
  • Individual cells and their organelles are drawn with accurate outlines, including features such as the nucleus.
Plan diagram
  • Low power drawing of tissue regions, showing the layers and boundaries only, with no individual cells drawn.
Electron micrographs
  • Interpret the ultrastructure, such as a prokaryotic cell or plant cell, and draw clear outlines of organelles.
Scale
  • Include a scale bar or magnification, so a reader can work out real sizes from the drawing.

Part 5 of 6Worked Example

Question

  • A scale bar in a drawing is 4.0 cm long and is labelled 20 µm.
  • The drawn cell is 8.0 cm wide.
  • Find the magnification and the real width of the cell.

  1. Convert 4.0 cm to micrometres: 4.0 × 10 000 = 40 000 µm.
  2. Magnification = 40 000 ÷ 20 = 2000.
  3. Convert the drawn width8.0 cm = 80 000 µm.
  4. Actual width = 80 000 ÷ 2000 = 40 µm.

Answer The magnification is ×2000 and the cell is 40 µm wide.

Part 6 of 6Exam Checklist & Tips

1.3.10 – Key Points for the Exam

  • Biological drawing A line drawing of the features observed in a specimen.
  • Plan diagram A low power drawing that shows the arrangement of tissues but not cells.
  • Annotation A note on a drawing that describes or explains a feature.
  • Scale bar A line on an image that represents a known actual length.
  • Magnification The ratio of image size to actual size.

Common Mistakes

  • Shading or colouring the drawing, which hides detail and is not allowed in biological drawings.
  • Drawing cells inside a plan diagram; only tissue boundaries are shown in a plan.
  • Crossing label lines or using arrowheads, which makes it unclear what each label points to.
  • Leaving out the title or magnification, which makes the drawing impossible to interpret.

Last updated:

Cambridge 9700 AS Biology Core Formula

Magnification Triangle & Unit Conversion

Formula: M = I / A  ⇔  A = I / M  ⇔  I = M × A

Units: 1 mm = 1,000 μm = 1,000,000 nm.
Rule: Convert Image size (ruler mm) to μm by ×1,000 before dividing by Actual size.