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Date	May 2018	Marks available	3	Reference code	18M.2.SL.TZ1.3
Level	Standard level	Paper	Paper 2	Time zone	Time zone 1
Command term	Explain	Question number	3	Adapted from	N/A

Question

Using the Punnett grid, explain how two parents can have children with any of the different ABO blood groups.

[3]

Distinguish between the structure of arteries and the structure of veins.

[3]

Explain how cuts in the skin are sealed by blood clotting.

[2]

Markscheme

a. correct gametes of one parent as I^A AND i in header line/column
AND
correct gametes of other parent as I^B AND i in header column/line

b. correct corresponding genotypes in inner squares as I^AI^B, I^Ai, I^Bi, ii

c. corresponding phenotypes of children identified as AB, A, B and O

d. ratio of phenotypes is 1:1:1:1 OWTTE

Allow ECF.

a. arteries have thicker (muscular) walls/layer/tunica (media)
OR
veins have thinner (muscular) walls/layer/tunica (media)

b. arteries have no valves
OR
veins have valves

c. arteries have thicker elastic layer
OR
veins have thinner elastic layer

d. arteries have a smaller lumen/bore
OR
veins have a larger lumen/bore

Accept answers presented in a table.

a. clotting factors released from platelets

b. clotting process involves a cascade/series of reactions

c. produces thrombin