Final answer:
In positive feedback, effectors amplify the changes caused by a stimulus in the same direction, intensifying the response until an external factor halts the process. This mechanism is essential in biological processes like childbirth and blood clotting.
Step-by-step explanation:
In positive feedback, the action of effectors amplifies changes in a variable, until an external stimulus is applied. A positive feedback loop is a control mechanism that serves to intensify a response until an endpoint is reached. It involves a reaction to some stimulus in the same direction as the stimulus, thus amplifying the effect. For example, during childbirth, uterine contractions are intensified until delivery is achieved; this is regulated by the hormone oxytocin.
Positive feedback leads to an unstable, runaway process—like exponential growth. It's different from negative feedback, which involves a response in the opposite direction of the stimulus, acting to stabilize the system.
While less common than negative feedback in biological systems, positive feedback is crucial in certain biological processes such as blood clotting, where a cascade of reactions continues to amplify until a fibrin clot is formed.