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Date May 2017 Marks available 3 Reference code 17M.2.HL.TZ1.6
Level Higher level Paper Paper 2 Time zone Time zone 1
Command term Describe Question number 6 Adapted from N/A

Question

Defence occurs on the micro and macro levels.

Describe the functioning of immunoglobulins.

[3]
a.

Outline how antibiotics offer protection from certain forms of infectious disease.

[4]
b.

Coughing to clear the airways is accomplished by muscle contractions. Explain muscle contraction.

[8]
c.

Markscheme

a. «immumoglobulins are/function as» antibodies 

b. variety of binding sites / variable regions for binding 

c. specific to antigens on bacteria/viruses/pathogens 

d. constant region aids destruction of the bacteria/virus/pathogen 

e. attracts phagocytes/macrophages to engulf pathogen 

f. bursting pathogen cells/agglutination/neutralizing toxins/other example of the action of antibodies

Award marks for an annotated diagram.

a.

a. protect against/kill/inhibit growth of microorganisms/bacteria/prokaryotes 

b. bacteria/prokaryote processes blocked but not processes in eukaryotes/other organisms 

c. block metabolic pathways/DNA replication/DNA transcription/translation/ribosome functioning/cell wall formation 

d. do not protect against viruses as they have no metabolism/are non-living 

e. antibiotics fail to protect if bacteria have resistance 

f. can be used in humans/animals because antibiotics do not affect eukaryotic cells/bacterial metabolism is different

b.

a. myofibrils «in muscle fibers/cells» 

b. sarcomeres «are the repeating units in muscle/myofibrils» 

c. sarcomeres arranged end to end / sarcomeres shorten during muscle contraction 

d. actin and myosin/overlapping protein filaments/diagram to show sarcomere with actin and myosin overlapping 

e. dark and light bands «in sarcomeres»/diagram to show this/light bands narrower when muscle is contracted 

f. thick filament is myosin and thin filament is actin/diagram to show this 

g. nerve impulses stimulate contraction/cause depolarization of sarcolemma/T-tubules/trigger release of calcium from sarcoplasmic reticulum 

h. calcium ions released from sarcoplasmic reticulum/bind to troponin 

i. troponin causes tropomyosin to move/exposes binding sites on actin 

j. myosin «heads» form cross bridges with/bind to actin 

k. myosin heads move/change angle/swivel/cock / myosin heads cause the power stroke 

l. myosin filaments pull actin towards center of sarcomere/more overlap between actin and myosin/Z-lines move closer 

m. ATP is used «to provide energy»/cause cross-bridges to break/cause movement of myosin heads/cause filaments to slide/cause muscle contraction 

n. intercostal/abdominal/diaphragm muscles contract «to cough»

Marks can be awarded for any point made clearly on an annotated diagram.

c.

Examiners report

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Syllabus sections

Core » Topic 2: Molecular biology » 2.4 Proteins
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