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Date November 2019 Marks available 7 Reference code 19N.2.HL.TZ0.7
Level Higher level Paper Paper 2 Time zone TZ0 / no time zone
Command term Explain Question number 7 Adapted from N/A

Question

Outline the reasons for the differences in blood concentrations between the renal artery and the renal vein.

[4]
a.

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

[4]
b.

Explain the control mechanism of the heart rate.

[7]
c.

Markscheme

a. urea/waste products lower in vein due to excretion «in urine»/ultrafiltration but not reabsorption ✔

b. oxygen lower in vein due to use in cell respiration/in kidney tissue ✔

c. carbon dioxide higher in vein due to production by cell respiration/excretion by kidney cells ✔

d. glucose lower in vein due to use in cell respiration «by kidney tissue» ✔

e. sodium/chloride/ion concentrations changed due to production of hypertonic/hypotonic urine
OR
sodium/chloride/ion concentrations lower due to removal of excess ✔

f. ion/solute concentrations lower in vein than artery if ADH has been secreted
OR
ion/solute concentrations in vein vary depending on amount of water reabsorbed in the collecting duct ✔

g. drug/toxin concentrations lower in vein due to excretion in urine ✔

Accept any point given as the converse.

Each mark point includes a difference and reason for it.

a.

a. IA, i for one set of gametes/parental genotype ✔

b. IB, i for the other set of gametes/parental genotype ✔

c. «genotypes of offspring are» IAIB, IAi, IBi, ii ✔

d. «phenotypes of offspring are» AB, A, B, O ✔

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

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

b.

a. sinoatrial node/SAN is a specialized group of muscle cells
OR
sinoatrial node/SAN is located in the right atrium ✔

b. acts as a pacemaker/controls the heart rate
OR
initiates/generates the heart beat/starts the cardiac cycle ✔

c. sends out electrical signal/impulses/depolarisations ✔

d. electrical signal stimulates contraction «of heart muscle» ✔

e. signal passes through walls of atria/passes to AV node ✔

f. then through walls of the ventricles ✔

g. medulla «oblongata of brain» can change/increase/decrease the rate ✔

h. through nerves/named example of nerve/autonomic/sympathetic/ parasympathetic nervous system ✔ In mph, only accept vagus nerve for slowing heart rate and sympathetic nerve for accelerating it.

i. one nerve increases the rate and the other decreases it ✔

j. epinephrine/adrenaline increases heart rate/force of contraction ✔

k. epinephrine/adrenaline prepares the body for vigorous activity/is part of fight or flight response ✔

c.

Examiners report

[N/A]
a.
[N/A]
b.
[N/A]
c.

Syllabus sections

Core » Topic 6: Human physiology » 6.2 The blood system
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