The answer is C. An effector is analogous to the way a ligand (of a stimuli) binds to receptors on the surface of the body and triggers an impulse in the neuron. An effector, on the other hand, occurs internally of the body and when the effector molecule binds to the receptors of the organ that it stimulates or suppresses, a cascade signaling pathway in the cells occurs and the cells/organs responds requisitely.
Answer:
Extrinsic regulatory mechanisms are external and depend on the firing of some factor outside the population itself. Among them are interspecific competition, food and space restrictions, very strong climatic variations, weathering and inharmonious relationships with other populations (parasitism and predatism).
Good examples of interspecific competition appear when rabbits, caves, rats compete for the same plant, or different fish and birds, such as the heron, vie for the same species of smaller fish. This is because these different species keep their populations in the same ecological niche. Competition is often so strong that some species eventually, as one example of an extrinsic homeostatic mechanism overriding an intrinsic homeostatic process is their disappearance or migration to other regions.
In this competition, the presence of adaptations among individuals in the population that promote better food search, speed, vision, and others can make the difference between elimination and survival.
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