The incidence of coronary heart disease (CHD) was investigated among 14 000 people. Baseline measurements of the waist to hip ratio and body mass index (BMI) were collected from the participants. After six years, evidence of CHD was identified in follow-up interviews. The bar chart shows the results for the men only.

Deduce with a reason whether the waist to hip ratio or the BMI most clearly correlates to incidence of CHD.

Explain how electrical signalling in the heart leads to ventricular contraction

Waist to hip ratio as increasing ratio shows increasing CHD incidence/increasing BMI does not

Reason required

Cardiac muscle transmits electrical signals
OR
cardiac muscle is myogenic

SA node initiates signal

Signal spreads over atria

Reaches the AV node

Signal passes through bundle of His/Purkinje fibres

Signal delayed at AV node/bundle of His

Delay allows ventricles to fill «as atria contract»

Conducting fibers spread signal across ventricle walls

Ventricles contract

Both parts (a) and (b) were well answered.

Both parts (a) and (b) were well answered with many full mark answers explaining how electrical signalling leads to ventricular contraction.