Q4. Define a cardiac cycle and the cardiac output. (NCERT Exercise 12)
The cardiac cycle is the sequence of events in the heart, cyclically repeated, made up of the systole and diastole of both the atria and the ventricles. The cardiac output is the volume of blood pumped out by each ventricle per minute, the stroke volume times the heart rate, about 5000 mL in a healthy person (NCERT page 200).
Q5. Write the differences between open and closed systems of circulation. (NCERT Exercise 7b)
In an open system, as in arthropods and molluscs, blood from the heart passes through large vessels into open spaces or body cavities called sinuses. In a closed system, as in annelids and chordates, blood always circulates in a closed network of vessels, so its flow can be regulated more precisely (NCERT page 197). Beyond the NCERT text: cephalopod molluscs, such as octopuses and squid, have a closed system (Villanueva and colleagues, Frontiers in Physiology, 2017).
Q6. Draw a standard ECG and explain the different segments in it. (NCERT Exercise 14)
See the figure on this page. The P-wave is the depolarisation of the atria, leading to their contraction; the QRS complex is the depolarisation of the ventricles, which starts ventricular contraction shortly after Q; the T-wave is the repolarisation of the ventricles, and NCERT associates its end with the end of systole (NCERT page 201).
Q7. Assertion: the semilunar valves open during ventricular systole. Reason: ventricular pressure exceeding the pressure in the pulmonary artery or aorta forces them open. Are both true, and does the reason explain the assertion?
Both are true, and the reason explains the assertion (NCERT page 200).