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Date May 2018 Marks available 4 Reference code 18M.2.SL.TZ1.6
Level Standard level Paper Paper 2 Time zone Time zone 1
Command term Explain Question number 6 Adapted from N/A

Question

Outline the role of the parts of an alveolus in a human lung.

[4]
a.

Explain how antibiotic resistance can evolve in bacteria, such as those causing pneumonia.

[4]
b.

Many diseases are caused by bacteria and other pathogens. Explain, using examples, how other factors can lead to disease in humans.

[7]
c.

Markscheme

a. the (spherical) wall of an alveolus maximizes/allows gas exchange 

b. pneumocytes I (optimize) gas exchange 

c. pneumocytes II produce surfactant 

d. adjacent capillaries enclose alveolus for efficient gas exchange with blood 

e. surfactant reduces surface tension/prevents collapse of alveolus

f. (alveolar) macrophages/phagocytes help with defense/homeostasis/response to foreign substances

a.

a. antibiotic resistance exists as a genetic variation (within the population) 

b. (antibiotic resistance) may occur from transfer of genetic material
OR
(antibiotic resistance) may occur through mutation 

c. resistance is specific to one antibiotic 

d. only bacteria with resistance gene reproduce in the presence of antibiotic 

e. frequency of resistant bacteria increases in population 

f. resistant population replaces non-resistant over time

b.

Since this question is open-ended here is how it may be marked:
For any non-pathogenic disease being addressed, look for the following components
● name of disease/condition.
● factor/category e.g.: genetic, lifestyle, environmental, psychological, multi-factoral.
● description/symptoms of disease.
● cause of disease.

At least 2 of these qualities must be present to earn any marks for a disease or category/factor
For this question use the unlettered tick. Award 4 MAX if only one condition is explained.

Sample answers:
e.g.
cystic fibrosis 

genetic 

multiple lung infections/sticky mucus allows opportunistic bacterial infections of lungs / patients lack lipases/cannot digest fat/do not “thrive” 

recessive (autosomal) allele / homozygous recessive subjects display cystic fibrosis phenotype / chloride channels are faulty 

e.g.
rickets 
environmental / lifestyle / nutritional 
bones are soft/do not calcify 
lack of vitamin D

c.

Examiners report

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

Syllabus sections

Core » Topic 6: Human physiology » 6.3 Defence against infectious disease
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