National League for Nursing (NLN PAX) Practice Exam

The respiratory system is considered the most complex level of organization in a frog because it encompasses various tissues and organs that work together to perform the intricate functions necessary for gas exchange. This system includes structures such as the lungs, bronchi, and alveoli, where oxygen is absorbed, and carbon dioxide is expelled.

Unlike the other options, which are more singular in structure or function, the respiratory system involves a coordination of multiple components: the airways for the passage of air, the respiratory surfaces for gas exchange, and associated muscles that facilitate breathing. This multi-organ system integrates with the circulatory system to ensure that oxygen reaches the tissues and that waste gases are removed efficiently.

In contrast, options like epithelium, striated muscle, and the stomach represent more localized or specific organizations within the body. Epithelium refers to a type of tissue that covers surfaces, striated muscle denotes a specific type of muscle tissue responsible for voluntary movements, and the stomach is an individual organ that plays a role in digestion. While all these components are important for the overall functioning of a frog, the respiratory system embodies a higher level of complexity due to its integration of various functional parts working in concert towards a common physiological goal.