Final answer:
The fish heart and circulatory system are an important evolutionary change because they demonstrate the transition from simple to complex life-sustaining systems. They mark the advent of closed circulatory systems in vertebrates, which allowed for greater metabolic efficiency and a higher oxygen supply, setting the stage for the diverse range of organisms we see today.
Step-by-step explanation:
The fish heart and circulatory system represent significant evolutionary steps because they demonstrate the transition from simple to more complex systems for sustaining life. As organisms became more complex and as demands for oxygen and nutrients increased, especially with the transition to terrestrial living, closed circulatory systems evolved. Fish have a two-chambered heart with a single circuit for blood flow that limits the amount of oxygen reaching body tissues, thus capping their metabolic capacity. This evolutionary stage set the groundwork for the development of more sophisticated circulatory systems in other vertebrates, such as amphibians, reptiles, birds, and mammals.
As depicted in figures labeled 31.4 and 40.4, fish blood flows unidirectionally from the heart through the gills for oxygenation, then through the body, representing the precursor to the dual-circuit systems seen in other vertebrates. Birds and mammals eventually evolved a four-chambered heart which completely separates oxygenated from deoxygenated blood, resulting in a more efficient system. This evolutionary adaptation is crucial for terrestrial life, where a higher metabolic rate and efficient oxygen delivery are necessary for survival.
Importance of Evolutionary Changes in Circulatory Systems
- Provides oxygen and nutrients to body cells.
- Removes wastes and helps regulate temperature.
- Enables more active and complex life forms.