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Question 19N.2.SL.TZ0.6

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Date November 2019 Marks available [Maximum mark: 15] Reference code 19N.2.SL.TZ0.6
Level SL Paper 2 Time zone TZ0
Command term Explain, Outline Question number 6 Adapted from N/A
6.
[Maximum mark: 15]
19N.2.SL.TZ0.6
(a)

Outline how cuts in the skin are sealed to prevent blood loss.

[4]

Markscheme

a. platelets respond to/detect skin/blood vessel damage ✔

b. platelets release clotting factors ✔

c. clotting factors trigger a chain/cascade of reactions ✔

d. «leading to» formation of thrombin ✔

e. thrombin causes fibrinogen conversion into fibrin ✔

f. blood clot seals the wound due to fibrin network of fibres ✔

Accept answers presented as a flow chart.

(b)

Outline how two parents could have a child with any of the four ABO blood groups.

[4]

Markscheme

a. «first set of» gametes/parental genotype IA, i ✔

b. «other set of» gametes/parental genotype IB, i ✔

c. «genotypes of offspring are respectively» IAIB, IBi, IAi, ii ✔ All four correct required.

d. «phenotypes of offspring are respectively» AB, B, A, O ✔ All four correct required linked to genotypes

Award marks only for the first grid if more than one drawn;
e.g. of Punnett grid

Answers can be given in a Punnett grid or in prose.

Accept the four possible blood groups of the offspring anywhere in the answer.

(c)

Explain how ventilation and lung structure contribute to passive gas exchange.

[7]

Markscheme

a. air carried through trachea AND bronchi/bronchioles AND alveoli ✔ All three required in correct order.

b. alveoli increase the surface area/thin walled for gas exchange ✔

c. gas exchange carried out through type I pneumocytes ✔

d. type II pneumocytes secrete surfactant to reduce surface tension ✔

e. moist surface/surfactant allows gases to diffuse in solution ✔

f. ventilation/moving blood maintains concentration gradients of oxygen and carbon dioxide ✔

g. between air in alveoli and blood in «adjacent» capillaries
OR
oxygen diffuses from alveoli to capillaries and carbon dioxide from capillaries to alveoli ✔ OWTTE

h. external intercostal muscles/diaphragm contract during inspiration ✔

i. lowering air pressure «in lungs»/increasing thorax volume ✔

j. relaxation of external intercostal muscles/diaphragm enable «passive» expiration ✔

k. internal intercostal «and abdominal muscles» contract «to force» expiration ✔

l. expiration due to increasing air pressure «in lungs»/decreasing thorax volume ✔

Accept correctly annotated diagram.

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