The heart and mammalian circulationEdexcel A-Level Biology B: Mind map

Exam questions on The heart and mammalian circulation

1. A bony fish has a heart with one atrium and one ventricle. Blood leaves the heart, passes through the narrow capillaries of the gills, and then flows on to the capillaries of the body tissues before returning to the heart. A mammal has a heart with four chambers, and its blood returns to the heart after the lungs before it is sent to the body.
   Explain why blood reaches the body tissues of the fish at a lower pressure than blood reaches the body tissues of the mammal.2 marks
2. In a resting adult the heart beats 75 times per minute, and the left ventricle ejects 70 cm³ of blood with each beat. During each cardiac cycle the pressure in the left ventricle first rises above the pressure in the left atrium, and a little later rises above the pressure in the aorta.
   Calculate (i) the duration of one cardiac cycle and (ii) the cardiac output of the adult, in cm³ per minute.2 marks
3. A cardiologist examines the electrocardiogram (ECG) of a patient. The trace shows regular P waves, but some P waves are not followed by a QRS complex, and when the QRS complex does occur the delay after the P wave is longer than normal.
   Explain how the delay between the P wave and the QRS complex is produced in a healthy heart and why the delay is important.3 marks