Biology Regents Practice Exam 2026 – The All-in-One Guide to Master Your Regents!

Mammals like dolphins are distinguished from fish like sharks primarily by their ability to regulate their body temperature, a characteristic known as being warm-blooded (endothermic). This means that mammals can maintain a stable internal temperature regardless of their environment, which allows them to be active in various habitats, including colder waters. On the other hand, fish such as sharks are typically cold-blooded (ectothermic), meaning their body temperature fluctuates with that of their surroundings.

This difference in thermoregulation plays a significant role in the ecological niches these animals occupy. Warm-blooded mammals can generate energy and sustain activity levels in colder environments, whereas cold-blooded fish are limited to the temperature of the water they inhabit.

The other choices do not accurately reflect the key distinctions between mammals and fish. For instance, mammals do not have gills; instead, they possess lungs for breathing air. While some fish can give live birth, this is not a universal trait among them, as many lay eggs. Lastly, both mammals and fish belong to different classes within the animal kingdom, specifically Mammalia and Chondrichthyes (for sharks), emphasizing the fundamental differences between these two groups rather than any shared phylum.