2.7.2Inquiry Process
Identify Blood Vessels- Skills — IB Biology HL Revision Notes & Topical Questions
5 min read 5 parts Lesson 74 of 160
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.
Section 1 of 5Clues in a Transverse Section
Relative thickness is a more reliable clue than colour or absolute size.
Artery
- Artery Appears round with a thick wall, a small lumen and often a wavy inner lining because the elastic tissue has recoiled.
Vein
- Vein Appears thinner walled and often irregular or collapsed, with a larger lumen compared with the artery next to it.
Capillary
- Capillary Appears as a tiny tube with a wall just one cell thick and red blood cells passing through in single file.
Companions
- Companions In tissue sections an artery and its accompanying vein often lie side by side, which makes comparison easy.
Section 2 of 5Step-by-Step Identification
1
Look at the overall shape: is the section round and regular or flattened and irregular?
2
Compare the thickness of the wall with the width of the lumen.
3
Look for layers of muscle and elastic tissue, which are thick in arteries and thinner in veins.
4
Check the lumen width: a large open lumen suggests a vein, while a very small tube with one-cell wall suggests a capillary.
5
State your conclusion with two or more features as evidence, linking them to function.
Section 3 of 5Measuring and Calculating
Measuring and Calculating
Magnification
- Magnification Calculate magnification by dividing the measured image length by the real length, or use the scale bar if one is given.
Actual size
- Actual size Actual size equals measured size divided by magnification, so a 24 mm image at ×60 represents 0.4 mm.
Wall to lumen ratio
- Wall to lumen ratio Dividing wall thickness by lumen diameter gives a number that is larger in arteries than in veins.
Units
- Units Convert measurements to the same unit, such as micrometres, before dividing.
| Vessel | Wall thickness (mm) | Lumen diameter (mm) | Ratio |
|---|---|---|---|
| Artery | 1.2 | 3.0 | 0.40 |
| Vein | 0.3 | 4.5 | 0.07 |
Section 4 of 5Worked Example
Question
- In a micrograph the wall of an artery measures 6 mm and its lumen measures 15 mm.
- The magnification is ×5.
- Calculate the actual wall thickness and the wall to lumen ratio.
- Actual wall thickness = 6 ÷ 5 = 1.2 mm.
- Actual lumen diameter = 15 ÷ 5 = 3.0 mm.
- Ratio = 1.2 ÷ 3.0 = 0.40.
Answer The wall is 1.2 mm thick and the wall to lumen ratio is 0.40.
Section 5 of 5Exam Checklist & Tips
2.7.2 – Key Points for the Exam
- Transverse section A cut at right angles to the long axis of a structure.
- Wall to lumen ratio Wall thickness divided by lumen diameter, used to compare vessels.
- Scale bar A line on an image that represents a known real length.
- Micrograph An image taken through a microscope.
Common Mistakes
- Using colour alone to decide between artery and vein;
- stained sections do not follow the red and blue convention.
- Measuring wall thickness at an angle rather than across the wall.
- Forgetting to convert units before calculating magnification.
- Giving only one feature as evidence rather than relating wall, lumen and function.
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