| Date | November 2016 | Marks available | 2 | Reference code | 16N.2.SL.tz0.3 |
| Level | Standard Level | Paper | Paper 2 | Time zone | time zone 0 |
| Command term | Outline | Question number | 3 | Adapted from | N/A |
Question
List one type of blood cell.
State the receptor in the aorta which responds to carbon dioxide and pH levels in the blood.
Outline the role of cholinesterase in muscle contraction.
Explain the role of myosin in muscle contraction after adenosine triphosphate (ATP) is broken down and releases energy.
Markscheme
erythrocytes/red blood cells ✔
leucocytes/white blood cells ✔
platelets/thrombocytes ✔
Any correct name of a type of white blood cell would be accepted, eg neutrophils, monocytes, eosinophils and basophils.
«peripheral» chemoreceptors ✔
degrades/breaks down Acetylcholine/Ach «within 5 milliseconds» ✔
immediately repolarizes the membrane ✔
stops synaptic transmission of impulse
OR
allows the muscle to relax ✔
myosin head tilts toward actin to attach to exposed binding site «to form a cross-bridge» ✔
myosin head drags actin and myosin filaments in opposite directions/performs a power stroke/generation of force ✔
pulling of the actin filament past the myosin results in muscle/sarcomere/Z line shortening ✔
the myosin head detaches from the actin when an ATP molecule binds to the myosin head ✔
repeated attachments and power strokes cause the filaments to slide/contract past one another ✔
H-zone disappears «and thus shortens» ✔
Examiners report
Another strong question for many candidates, with most candidates responding with erythrocytes. Very few candidates identified platelets.
Generally candidates answered this accurately; however there were a number of candidates who confused this for the sinoatrial node.
Many candidates scored 1 mark for this question identifying that cholinesterase is the enzyme which breaks down acetylcholine. However, there is still a misconception that cholinesterase is a neurotransmitter. Cholinesterase is also known as acetylcholinesterase.
Overall this question was answered well, although many candidates failed to recognise the specific focus of this question and discussed the synapse and depolarisation of the muscle and changes to troponin and tropomyosin which were irrelevant to this question.
