Biological drawings

25 min

Why draw when you can photograph?

Every student has a phone camera somewhere nearby, so why do biology exams still ask you to draw a specimen? Because drawing forces you to look. A photograph records everything, including dirt, shadows and air bubbles; a drawing records what you have understood: which lines are real edges, which parts matter, and how big they are compared with each other. Robert Hooke's drawings of cork cells in 1665 and the botanists' drawings of Nyungwe's plants today follow the same principle.

Definition

Biological drawing: an accurate, clearly labelled line drawing of a specimen, made from direct observation, with a title and a statement of magnification. It is a scientific record, not a work of art.

Label line (leader line): a straight, ruled line joining a label to the part it names.

A good drawing and a poor one

Figure 1: The same specimen drawn well and badly. The numbered faults in the poor drawing are explained below.

Faults in the poor drawing: (1) sketchy, doubled outlines instead of one clean line; (2) shading; (3) arrowheads on label lines, and label lines that cross; (4) labels written at angles, in mixed capitals and sizes; (5) the drawing is small, and it has no title and no magnification.

Rule	Reason
Use a sharp HB pencil and plain paper.	Pencil can be rubbed out; a sharp point gives thin, precise lines.
Draw large: at least half a page.	Details are clear and can be labelled without crowding.
Use single, clean, continuous lines.	Each line should show one real edge; sketchy lines hide where the edge is.
Do not shade or colour.	Shading hides detail and can be mistaken for real structures.
Keep the proportions accurate.	Parts must be the right size compared with one another.
Rule label lines with a ruler; no arrowheads; lines must not cross.	Each label must point clearly and exactly to one part.
Print labels horizontally, in a neat column to one side.	Labels are easy to read and do not cover the drawing.
Add a title with the view and the magnification.	The reader knows what was drawn, from which side, and how large it really is.
Draw only what you see.	A drawing is a record of observation, not of a textbook diagram you remember.

Worked example 1: stating the magnification of your drawing

Niyonzima measures a bean seed: 14 mm long. His drawing of it is 70 mm long. What does he write in the title?

\text{magnification} = \frac{\text{length of drawing}}{\text{actual length}} = \frac{70\ \text{mm}}{14\ \text{mm}} = 5

Answer: "A bean seed: external view (×5)". Measure the same line on the specimen and on the drawing, usually the greatest length.

Worked example 2: drawing what you see under a microscope

Under the ×10 objective, Umutoni sees about sixty onion epidermis cells. Her first attempt shows all sixty, each the size of a grain of rice, with the nuclei shaded black. How should she improve it?

Draw fewer cells, larger: three or four neighbouring cells, filling at least half the page, are enough to show their shape and how they fit together.
Show the real structures with clean lines: the cell walls, and the nucleus of each cell drawn as an outline, not a black blob.
Label "cell wall", "cytoplasm" and "nucleus" with ruled lines, in a column to the right.
Title and magnification: for example "Onion epidermis cells, surface view, as seen at ×100" (her microscope's magnification, since she drew what she saw at that setting).

Answer: a few large, accurate, labelled cells are worth far more than many tiny, shaded ones.

Warning

Do not draw the textbook. A common mistake is to draw a neat diagram remembered from a book instead of the actual specimen on the bench. Examiners check that the drawing matches the specimen they gave you: its shape, the number of parts, even a torn edge. Draw what is in front of you.

Drawing in Rwandan classrooms and exams

In national examinations you may be asked to draw a specimen such as a seed, a flower, a leaf or an insect, label it and state its magnification; marks are given for each rule in the table. The same skill is used by field scientists recording new plant species in Nyungwe, where a careful drawing can show features that a photograph blurs. Practise on specimens from home: a bean seed, a maize grain, a hibiscus flower cut in half.

Perfect Biological Drawings (D Biology Classroom). It is aimed at older students, but the rules are exactly the same: watch for line quality, label lines and the title.

Tip

Memory hook: "Big, clean, ruled, titled." Draw it big, keep the lines clean, rule the label lines, and give it a title with the magnification.

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Practice: biological drawings

Why should a biological drawing be done in pencil, not pen?
List four rules for label lines and labels.
Why is shading not allowed in a biological drawing?
A maize grain is 10 mm long and your drawing is 80 mm long. What magnification do you write in the title?
Your drawing of a leaf is 150 mm long and the magnification is ×0.5. How long is the real leaf?
Write a suitable title for a drawing of a hibiscus flower cut in half lengthways, drawn twice its real size.
A classmate's drawing is excellent, but she added colour to make the petals look real. Evaluate this choice.

Show answersHide answers

Pencil can be rubbed out to correct mistakes, and a sharp pencil gives thin, precise lines.
Any four: ruled with a ruler; no arrowheads; lines must not cross; lines touch the part they name; labels printed horizontally; labels in a neat column to one side.
It hides detail and can be mistaken for real structures; a drawing should show edges with clean lines only.
$\frac{80\ \text{mm}}{10\ \text{mm}} = 8$ , so ×8.
$\text{actual length} = \frac{150\ \text{mm}}{0.5} = 300\ \text{mm}$ , that is 30 cm: the drawing is smaller than the leaf, so the magnification is less than 1.
For example: "Hibiscus flower: half-section (longitudinal section) ×2".
It breaks the rules of biological drawing: colour (like shading) can hide detail and is not needed to show structure. The drawing should show the petals with clean outlines; colour belongs in art, not in a scientific record.

Key points

Draw large, in sharp pencil, with single clean lines and no shading or colour.
Rule label lines without arrowheads, never crossing, with labels printed horizontally to one side.
Give a title with the view and the magnification: drawing size ÷ actual size.

1Why draw when you can photograph?

2A good drawing and a poor one

3Drawing in Rwandan classrooms and exams

Why draw when you can photograph?

A good drawing and a poor one

Drawing in Rwandan classrooms and exams