Define the term centre of mass.

The diagram shows a gymnast performing a piked somersault.

[Source: www.gymdrills4profs.com.]

Explain the manipulation of the moment of inertia during the flight and landing phases.

The diagram shows skeletal muscle.

[Source: HENNING DALHOFF/SCIENCE PHOTO LIBRARY.]

Identify the parts labelled A and B.

A:

B:

Describe the sequence of excitation of the heart muscle.

A beginner participated in a seven-week tennis programme. Each week, they recorded their successful serves out of 50 attempts. Identify the type of learning curve represented by the data.

the point around which the mass of a body is evenly distributed

OR

the point which the body is balanced in all directions / OWTTE;

the manipulation of moment of inertia directly affects the gymnast's angular velocity in order to conserve angular momentum throughout the skill

OR

rotating objects have angular motion, moment of inertia and angular velocity work inversely to conserve angular momentum once an object is in motion;

the moment of inertia of a rotating object can be changed by redistributing the mass of the object about the axis of rotation <enabling the gymnast to perform a somersault>;

at the start of the flight phase, the gymnast begins flexes their hips to reduce their moment of inertia;

the reduction in moment of inertia increases angular velocity, this allows the somersault to be executed;

prior to landing they extend their hips to increase moment of inertia;

increasing moment of inertia reduces rotation / slows the gymnast for landing;

A: myofibril;

B: actin;

electrical impulse is generated by the sinoatrial (SA) node;

impulse travels across atria <exciting the tissue> and arrives at the AV/VA/atrioventricular node;

AV/VA node delays the impulse <0.1 sec> to allow time for atria to contract and force blood into ventricles;

impulse passes from the AV/VA node to the AV/VA bundle / bundle of His <into the bundle branches>;

impulse conducted rapidly through Purkinje fibres that spread along ventricle walls;

once stimulated the ventricles contract/pressure in ventricles forces blood out through main arteries leaving heart;

MPs can only be awarded in correct sequence order.

positive <acceleration>;

Most candidates attempted this question and were able to provide a suitable definition of centre of mass. Some candidates confused centre of gravity with centre of mass and further review of this concept would be beneficial for candidates.

It appeared that candidates either knew the concept or didn't, scoring either 4 marks or 0 marks. Candidates who struggled to access marks confused the relationship between angular momentum, angular velocity and moment of inertia or contradicted themselves. In terms of understanding the requirements of the question most candidates referred to the image and used this to break down their response to the question which was pleasing to observe.

Many candidates attempted this question and a large proportion were able to identify actin filament. However, candidates struggled with identifying myofibril. Many identifying muscle fibre or myofilament, further review of the structure with exposure to varying images may be beneficial to candidates.

The fewest number of candidates attempted this question in section A. The question did not refer to intrinsic or extrinsic regulation which may be common trigger words for candidates. The question was specifically focusing on the sequence of excitation of the heart muscle. Most candidates were able to outline the role of the SA node. Fewer were able to list the conducting structures along the sequence of excitation. Some confused the bundle of His with the AV node. Many candidates were unable to describe the sequence. Therefore, further practice of describing the sequence is required. Lists were a common occurrence.