The hormone epinephrine binds to ß adrenergic receptors on smooth muscle cells of the bronchioles, causing them to dilate (increase in diameter). Thyroid hormone is essential for the synthesis of ß adrenergic receptors; therefore, in the absence of thyroid hormone, epinephrine cannot trigger bronchodilation. This concept if known as .

The correct answer is "permissiveness".

Explanation:

The missing options of the question are:

permissiveness

synergistic effect

antagonism

additive effect

The correct answer is "permissiveness",

In biology, a permissive effect is defined as the effect that one hormone has enabling that a second hormone to exert its biological activity. Thyroid hormone has a permissive effect on the hormone epinephrine, by synthesizing ß adrenergic receptors, it enables the hormone epinephrine binds to them and cause the cells of the bronchioles to dilate.

if the type of the food available changes, then the frequency of beak types will change, because birds with beaks more suited to the available food will be more successful over time.