The primary difference between an amphibian and a reptile lies in their physiological characteristics and life cycles. Amphibians, such as frogs and salamanders, typically have a life cycle that includes both aquatic and terrestrial phases, often starting as eggs that hatch into larvae, which then undergo metamorphosis into adults. They possess permeable skin, which allows for gas exchange, making them dependent on moist environments. In contrast, reptiles, like snakes and lizards, lay eggs with hard shells or give live birth, and they have dry, scaly skin that minimizes water loss. These adaptations make reptiles better suited for arid environments compared to amphibians.