2.6.6Inquiry Process
Drawing Leaf Structure- Skills — IB Biology HL Revision Notes & Topical Questions
5 min read 5 parts Lesson 68 of 160
Part 1 of 5Tissues in a Dicot Leaf Section
Work from the top surface of the leaf downwards.
1
The waxy cuticle covers the upper epidermis and reduces water loss without blocking light.
2
The upper epidermis is a single transparent layer that protects the tissues below.
3
The palisade mesophyll, just beneath, has tall cells packed with chloroplasts for photosynthesis.
4
The spongy mesophyll has rounded cells and large air spaces that allow gas movement.
5
The lower epidermis contains stomata with guard cells, and veins (vascular bundles) pass through the middle with xylem above phloem.
Part 2 of 5Rules for Biological Drawings
Use a sharp pencil
- Draw clear, continuous single lines with no shading, sketching or overlapping, so every structure can be identified.
Plan diagram
- A plan diagram shows the outlines of tissues only and does not draw individual cells.
High-power diagram
- A detailed drawing of a small area shows cell walls and the shapes of cells, drawn with accurate proportions.
Labels
- Label lines are ruled with a ruler, touch the structure, never cross each other, and are placed at the side of the drawing.
Title and scale
- Add a title, the magnification or a scale bar, and keep the drawing large enough to fill at least half the space.
| Diagram type | Shows | Does not show |
|---|---|---|
| Plan | Tissue boundaries | Individual cells |
| High-power | Cell detail | Whole section |
Part 3 of 5Interpreting Magnification
Interpreting Magnification
Magnification
- Magnification equals the size of the image divided by the actual size of the specimen.
Scale bar
- A bar of known real length drawn on the diagram lets the viewer calculate sizes without a formula.
Units
- Convert millimetres to micrometres by multiplying by 1000 before comparing sizes.
Annotations
- Notes added to labels can state the function, such as 'palisade layer: most chloroplasts, photosynthesis'.
Part 4 of 5Worked Example
Question
- A leaf cross-section drawing is 90 mm wide.
- The actual section is 1.5 mm wide.
- Calculate the magnification.
- Magnification = image size ÷ actual size.
- Both must use the same units90 mm and 1.5 mm.
- 90 ÷ 1.5 = 60.
Answer The magnification is ×60.
Part 5 of 5Exam Checklist & Tips
2.6.6 – Key Points for the Exam
- Plan diagram A low-power drawing that outlines the distribution of tissues without showing cells.
- Palisade mesophyll The upper photosynthetic layer of tall, tightly packed cells rich in chloroplasts.
- Vascular bundle A vein containing xylem and phloem.
- Magnification How many times larger an image is than the real object.
Common Mistakes
- Shading or colouring a biological drawing, which is not allowed.
- Drawing cells in a plan diagram; only tissue outlines are needed.
- Allowing label lines to cross or end without touching the structure.
- Putting phloem above xylem in the vascular bundle; xylem is normally nearer the upper surface.
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