On the diagram, label a pair of antagonistic muscles.

State the function of the structure labelled A.

Explain the role of ATP in the contraction of skeletal muscle.

biceps and triceps correctly labelled; (biceps = muscle on right, triceps = muscle on left)
Both needed for mark.

(cartilage is hard but flexible) able to absorb mechanical shocks / allows bones to pivot or move smoothly

ATP binds to myosin heads;
ATP binding causes cross bridges to break/heads detach from binding site;
ATP broken down/hydrolysed to ADP + Pi, causing myosin heads to change angle/become “cocked”;
myosin heads attach to binding sites on actin filament further along sarcomere;
ADP + Pi released and myosin heads push actin filament along/power stroke occurs;
Allow ONE mark if there is a general understanding of the role of ATP in the sliding of filaments but without specific details.

Most candidates could label “antagonistic muscles” on the diagram, but very few could name them.

Many thought that structure A was simply the joint, and gave superficial responses such as “helps the arm to bend”, which did not gain any marks. Others said incorrectly that A was synovial fluid.

This challenging question proved to be a good differentiator for the more able candidates, as a lot of understanding and detail were required in order to gain the marks.