The correct option is (a).
Explanation
The heart is a muscular organ located in the chest cavity, responsible for pumping blood throughout the body. Its function relies on the coordinated action of specialized muscle tissue known as cardiac muscle.
Statement-wise Analysis
- Statement 1 is Correct: The walls of the heart chambers (atria and ventricles) are composed of cardiac muscles. These muscles are involuntary and striated, designed specifically for continuous pumping action without fatigue.
- Statement 2 is Incorrect: The contraction and relaxation of heart muscles occur in a rhythmic and coordinated manner, not randomly. This rhythmic contraction constitutes a heartbeat, which maintains the circulation of blood.
- Statement 3 is Incorrect: A doctor uses a stethoscope to listen to and amplify the sound of the heart. A thermometer is an instrument used to measure body temperature.
Key Takeaway
The heart is made of cardiac muscles that contract rhythmically to pump blood. The instrument used to amplify and listen to heart sounds is the stethoscope.