Biology / AS level
The cardiac cycle coordinates atrial and ventricular contraction with pressure-sensitive valves.
The cardiac cycle coordinates atrial and ventricular contraction with pressure-sensitive valves. Electrical excitation begins in pacemaker tissue and spreads through a conduction system; valves open because of pressure differences rather than active pulling.
Haemoglobin’s cooperative oxygen binding supports loading at high oxygen partial pressure and unloading in respiring tissues. Carbon dioxide is transported mainly after conversion to hydrogencarbonate, with additional dissolved and haemoglobin-associated forms. Vessel structure matches pressure, return and exchange roles.
Heart rate is 70 beats/min and stroke volume is 70 cm³/beat. Find cardiac output.
Multiply rate by volume per beat: 70×70=4900 cm³/min, or 4.9 dm³/min.
Using the worked example as supplied data, predict the effect of changing one condition. Draw a labelled model, record your reasoning and identify a variable that would need controlling. No human, animal or microbial experiment is required.
No exact PhET model is claimed for this topic. Use diagrams and supplied-data reasoning instead.
An appropriate pressure difference
Valve movement responds passively to pressures on its two sides.
4900 cm³/min
Multiply rate by volume per beat: 70×70=4900 cm³/min, or 4.9 dm³/min.
No
Oxygen loading and unloading respond to local partial pressure and conditions, especially in exchanging tissues.