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Date May 2017 Marks available 8 Reference code 17M.2.SL.TZ2.5
Level Standard level Paper Paper 2 Time zone Time zone 2
Command term Explain Question number 5 Adapted from N/A

Question

Draw a molecular diagram of an amino acid to show its general structure.

[3]
a.

Outline the role of ribosomes in translation.

[4]
b.

Some blood proteins are involved in defence against infectious disease. Explain the roles of named types of blood proteins in different defence mechanisms.

[8]
c.

Markscheme

a. COO– or COOH group at one end 

b. NH2 or NH3+ at the other 

c. CH in middle with H or R group attached

If shown expanded, then carbonyl oxygen must attach to C
If shown non-expanded, N of amine group must attach to C

a.

a. translation is the production of polypeptides/proteins 

b. mRNA binds to the ribosome 

c. tRNA binds to the ribosome 

d. at the site where its anti-codon corresponds to the codon on the mRNA

OWTTE

e. amino acids of «consecutive tRNAs» bind by a peptide link «in the ribosomes» 

f. the ribosome moves along the mRNA
OR
continues with elongation of polypeptide chain

Accept annotated diagrams of the process.

b.

a. clotting factors «are proteins» that initiate the clotting cascade/process 

b. fibrin «is a protein that» permits blood clotting
OR
allows the formation of a clot 

c. «the protease» thrombin converts fibrinogen to fibrin  

OWTTE

d. fibrin forms a mesh/clot that prevents the entry of pathogen/antigen into the blood 

e. antibodies are «specific» proteins that lymphocytes make 

f. each antibody corresponds to a specific pathogen/antigen
OR
antibodies are specific «to certain pathogens/antigens» 

g. antibodies create specific immunity 

h. plasma cells produce large amounts of «specific» antibodies
OR
memory cells retain the ability to produce «specific» antibodies 

i. immunoglobulins are antibodies against pathogens 

j. enzymes in phagocytic white blood cells may digest pathogens

Accept annotated diagrams of the process.

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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