2.6.6Additional lessons
Drawing Leaf Structure: Skills — IB Biology SL Revision Notes & Topical Questions
5 min read 5 parts Lesson 32 of 142
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 5Tissues to Show in a Leaf Section
In a plan diagram you show the arrangement of tissues, while in a cell drawing you show individual cells.
Cuticle and epidermis
- Cuticle and epidermis The upper and lower epidermis are single layers of cells, with the waxy cuticle as the outer layer on top.
Palisade mesophyll
- Palisade mesophyll A layer of elongated, closely packed cells below the upper epidermis that contain many chloroplasts.
Spongy mesophyll
- Spongy mesophyll Rounded, loosely packed cells with large air spaces between them near the lower surface.
Vascular bundle
- Vascular bundle A vein showing xylem and phloem, usually in the middle of the leaf.
Stomata and guard cells
- Stomata and guard cells Gaps in the epidermis, each bordered by two guard cells containing chloroplasts.
Part 2 of 5Drawing Method
1
Use a sharp pencil and draw clear, continuous lines, without shading or colouring.
2
Draw only what you can see, and use at least half of the page to give a large, clear drawing.
3
In a plan diagram show tissues as outlines without drawing individual cells.
4
Add label lines ruled with a ruler that touch the structure, with no arrowheads and no crossing lines.
5
Give the drawing a title and a scale or magnification, and state the type of section shown.
| Tissue | Position | Key feature |
|---|---|---|
| Upper epidermis | Top surface | Single layer, covered by cuticle |
| Palisade mesophyll | Below upper epidermis | Tall cells, many chloroplasts |
| Spongy mesophyll | Below palisade | Air spaces |
| Lower epidermis | Bottom surface | Stomata and guard cells |
Part 3 of 5Magnification and Scale
Magnification and Scale
Formula
- Formula Magnification = size of image ÷ actual size, with both measured in the same units.
Scale bar
- Scale bar A line on the drawing marked with the real length that it represents, which allows direct reading of size.
Unit conversion
- Unit conversion 1 mm = 1000 µm, so convert to the same unit before dividing.
Checking drawings
- Checking drawings Compare proportions, such as the thickness of palisade and spongy layers, with the micrograph.
Part 4 of 5Worked Example
Question
- In a drawing, the leaf section measures 84 mm across its thickness.
- The actual leaf thickness is 0.21 mm.
- Calculate the magnification.
- Magnification = image size ÷ actual size.
- Both are in millimetres84 mm ÷ 0.21 mm.
- 84 ÷ 0.21 = 400.
Answer The magnification is ×400.
Part 5 of 5Exam Checklist & Tips
2.6.6 – Key Points for the Exam
- Plan diagram A low-power drawing that shows the tissues and their arrangement, without individual cells.
- Magnification How many times larger the image is than the real object.
- Palisade mesophyll The upper mesophyll layer rich in chloroplasts.
- Guard cell A cell that controls the opening of a stoma.
Common Mistakes
- Drawing individual cells in a plan diagram, which should show only tissues.
- Using shading or colour in an examination drawing.
- Writing label lines that cross or have arrowheads.
- Dividing actual size by image size when calculating magnification.
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