This is one of the few topics where marks are given for what you leave out. A plan diagram shows tissue layers, not cells — so a beautifully detailed drawing of individual palisade cells, complete with chloroplasts, can score badly. Learn the rules and this becomes one of the easiest marks in the paper.
📚 What you need to know
You must be able to identify these in a dicotyledonous leaf: cuticle, upper and lower epidermis, palisade mesophyll, spongy mesophyll, air spaces, chloroplasts, guard cells, stomata and vascular bundles (xylem and phloem).
A plan diagram is drawn at low magnification and shows tissue layers only — no individual cells.
Use a sharp pencil, draw clear continuous lines, and do not shade.
Draw what you actually see, in accurate proportions, big enough to fill at least half the space.
Label lines: use a ruler, no arrowheads, lines must stop at the structure, must not cross, and labels are written horizontally.
What a plan diagram looks like
Compare this with the detailed cross-section on the previous page. Same leaf, same layers, but every individual cell has been left out on purpose.
The thing students find hardest is trusting that less is more here. If you catch yourself drawing chloroplasts, stop — you are drawing a high-power detail diagram, not a plan diagram, and the mark scheme will not reward it.
The rules, in two lists
The arrowhead rule catches people out most often, because arrows feel helpful. In a plan diagram a plain line that simply stops at the tissue is what is wanted.
Drawing it, step by step
🧩 A method that works under exam pressure
Look before you draw. Identify the top and bottom surfaces first — the palisade layer is always on the upper side, and stomata are usually on the lower side.
Draw the outer boundaries. Two long horizontal lines for the top and bottom of the section, sized to fill at least half the space available.
Add the tissue boundaries in order, working down: cuticle, upper epidermis, palisade, spongy, lower epidermis, cuticle. Keep the proportions as you actually see them.
Add the vascular bundle as a single outlined region, with a line separating xylem from phloem if visible.
Mark the stoma in the lower epidermis, showing the two guard cells either side of the pore.
Label last, using a ruler, horizontal writing, and lines that stop at the structure without crossing each other.
The most useful instruction on the whole page: draw what you actually see, not what a textbook diagram looks like. Real sections are uneven, and examiners are checking whether you observed the specimen or reproduced a memory.
Worked examples
WORKED EXAMPLE
A student draws a plan diagram of a leaf section but includes individual palisade cells with chloroplasts inside them, and shades the vascular bundle. Explain two ways the drawing does not meet the requirements of a plan diagram. [2]
Fault 1A plan diagram shows tissue layers enclosed by lines. Individual cells and their contents should not be drawn.Fault 2Shading is not permitted in a biological drawing — regions are distinguished by outlines and labelsDrawing it too small would be a third fault if the diagram fills less than half the space.
WORKED EXAMPLE
A micrograph of a leaf section is shown with one surface bearing a thicker waxy layer and several stomata on the opposite surface. State which surface is the upper epidermis and justify your answer. [2]
Step 1: use the stomataMost stomata are found in the lower epidermis, so the surface with the stomata is the underside.Step 2: state the answerThe surface with the thicker cuticle and no stomata is the upper epidermisThe palisade layer sitting directly beneath it confirms it.
💡 Exam tip
Read the command word. “Plan diagram” means layers only; “high power drawing” means individual cells.
Fill at least half the space provided. Small drawings lose marks even when accurate.
Use a ruler for every label line, and write labels horizontally even when the structure is not.
Never add arrowheads, and never let two label lines cross.
Get the proportions right — if the spongy layer is thicker than the palisade in the specimen, draw it that way.
Orientate correctly: palisade at the top, stomata at the bottom. Getting this the wrong way round undermines every label.
⚠ Common mix-up
Drawing individual cells in a plan diagram. The single most common error, and it is easy to avoid.
Shading to show different tissues. Use outlines and labels instead.
Using arrowheads on label lines. Plain ruled lines that stop at the structure.
Drawing the palisade layer at the bottom. It sits just below the upper epidermis.
Sketching from memory. Draw the specimen in front of you, uneven bits included.
Labelling at an angle to follow the structure. All labels are written horizontally.
Up next: Determining Stomatal Density — counting stomata on a nail varnish cast, and turning that count into a number per square millimetre.
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