IB Biology HL B3.2 Transport questions

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Question 1

Multiple choiceMedium1 mark

Wall thickness and lumen diameter were measured from four vessel micrographs. Which specimen is most consistent with an artery?

01002003004005006007008009001000020406080100120140160Lumen diameter / µmWall thickness / µmPQRS
Show answer and explanation

Answer: D. Arteries have a thicker wall relative to lumen diameter than veins. The wall-thickness-to-lumen-diameter ratios are P: 150/1000 = 0.15, Q: 30/300 = 0.10, R: 40/800 = 0.05 and S: 80/400 = 0.20. S has the greatest relative wall thickness.

A: chooses P by comparing absolute wall thickness alone; its wall is 150 µm, but its ratio is 0.15.
B: chooses Q by using the smallest lumen diameter alone rather than comparing wall thickness relative to diameter.
C: chooses R by reversing the criterion and selecting the smallest wall-to-lumen ratio.
Remember: identify an artery by its relatively thick wall, not by absolute wall thickness alone.

Question 2

Paper 2Hard16 marks

Histology technicians are testing whether vessel type can be identified from transverse micrographs. Specimen A has been independently identified as an artery and specimen B as a vein. Wall thickness and lumen diameter were measured in three micrographs of each specimen.

SpecimenWall thickness / mm (micrographs 1, 2, 3)Lumen diameter / mm (micrographs 1, 2, 3)
A0.48, 0.50, 0.523.0, 3.1, 3.2
B0.38, 0.40, 0.426.0, 6.2, 6.4

The relative wall thickness index is calculated as:

mean wall thicknessmean lumen diameter×100%\frac{\text{mean wall thickness}}{\text{mean lumen diameter}}\times 100\%
(a)

Calculate the relative wall thickness index for specimens A and B. Give each answer to one decimal place and show your working.

[4]
(b)

Describe the structural difference between specimen A and specimen B indicated by your results.

[3]
(c)

A further unknown specimen, C, is examined in three transverse micrographs. Its wall thickness measurements are 0.58, 0.60 and 0.62 mm; its lumen diameters are 7.8, 8.0 and 8.2 mm.

Calculate the relative wall thickness index for specimen C, giving your answer to one decimal place.

[2]
(d)

Identify specimen C as an artery or a vein. Explain why comparing only its absolute wall thickness with that of specimen A could lead to a different conclusion.

[3]
(e)

A colleague proposes using a universal cutoff of 10.0%: any vessel with an index above 10.0% is an artery and any vessel with an index below 10.0% is a vein. Evaluate this proposal using the results for A, B and C, and suggest one way to test the cutoff before using it to identify further micrographs.

[4]

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