Final answer:
The assertion that cardiac muscle only uses glucose as fuel is false; it can metabolize various substrates, including fatty acids and lactate, to produce ATP through aerobic respiration. Glycogen stored within the cells can also serve as an energy source. Cardiac muscle possesses autorhythmicity and a high mitochondrial concentration.
Step-by-step explanation:
The statement that cardiac muscle can only use glucose as a source of organic fuel is false. Cardiac muscle is versatile in its energy metabolism and, in addition to glucose, it can also utilize other substrates such as fatty acids and lactate. During aerobic respiration, which is the primary metabolic pathway in cardiac muscle cells, these substrates are metabolized within the mitochondria to produce ATP. Glycogen, which is stored in the cytoplasm, can also be used as a source of energy.
It is also important to mention that if cardiac muscle cells were prevented from undergoing aerobic metabolism, they would undergo glycolysis to produce ATP. However, this process is less efficient than aerobic respiration and cannot sustain the heart's function indefinitely. Additionally, cardiac muscle is known for its characteristic autorhythmicity and contains a high concentration of mitochondria to support its continuous and demanding energy needs.