Final answer:
Frog lungs are poorly developed as frogs rely on cutaneous respiration through their thin and moist permeable skin, which must remain moist to facilitate gas exchange. This makes them sensitive to environmental conditions and pollutants. They reside near water to maintain their skin's moisture for respiration.
Step-by-step explanation:
Frog lungs are poorly developed because frogs have permeable skin that allows for cutaneous respiration, an important source of gas exchange in amphibians. This permeability is a characteristic of extant amphibians, which means their skin must be thin and moist to facilitate this process. The thin and moist skin is covered with mucous glands that secrete mucus to keep the skin moist, necessary for the diffusion of gases. Frogs and toads, therefore, generally need to live in or near water or in moist environments to prevent water loss through their skin and to enable efficient respiration.
In comparison to humans and other mammals, which use a diaphragm for more efficient respiration, most adult amphibians lack or have a reduced diaphragm, meaning they must rely more on their skin for respiration. The presence of a dense network of capillaries just below the skin surface of amphibians greatly enhances this cutaneous gas exchange. Moreover, this delicate balance of respiration through both the skin and lungs means that amphibians like frogs can be particularly sensitive to environmental pollutants that can be readily absorbed through their skin.