Consider the following four statements (i)-(iv) and select the correct option
(i) Fish heart contains only oxygenated blood
(ii) Closure of A-V valves produces the second heart sound
(iii) The vascular connection between the digestive track and kidney is called hepatic portal system
(iv) Purkinje fibres are nerve fibres present in the heart wall.

Answer: BSolution: Fish special neutral centre in the medulla oblongata can moderate the cardiac function through autonomic nervous system (ANS) Neutral signals through the sympathetic nerves (parts of ANS) can increase the rate of heartbeat, the strength of ventricular contraction and thereby the cardiac output. On the other hand, parasympathetic neutral signals (another component of ANS) decrease the rate of heartbeat, speed of conduction of action potential and thereby the cardiac output.