Understanding Positive Feedback - High School Biology

During positive feedback the production of an effect stimulates amplification of the same effect. In contrast, during negative feedback the production of an effect stimulates the reduction of the same effect. The result of positive feedback is an exponential increase in the intensity of the effect, while the effect of negative feedback is a form of equilibrium around a constant level.

Oxytocin release during childbirth is one of only a few positive feedback mechanisms in the body. Almost all other processes are modulated by some form of negative feedback.

Contraction of the uterus during childbirth causes the release of oxytocin, which stimulates stronger contractions of the uterus, causing more oxytocin release. This perpetual cycle results in a positive feedback response.

Negative feedback is a system in which change initiates a series of events that tend to counteract the change and restore the original state. This makes negative feedback the essential mechanism for maintaining euqilibrium and homeostasis. When blood sugar levels rise, insulin is released and transports the glucose into the cells, thereby lowering blood glucose levels. When blood sugar levels are low, perhaps in between meals, glucagon is released. Glucagon causes stored glucose to be released, raising blood sugar levels. When you prespire and lose water, antidiuretic hormone is released causing your kidneys to reabsorb water. If blood caclium levels become too high, the thyroid releases calcitonin, which inhibits the release of calcium from the blood. All of these effects serve to counteract the change that initiated the hormone release.

In a positive feedback loop, an increase in quantity A leads to an increase in quantity B. An increase in B then loops back around to increase quantity A in a cycle that continues unless broken in some way.

In this case, the option dealing with climate change and methane is an example of a positive feedback loop because as the climate warms (quantity A increases), more methane is released (quantity B increases). We are told that methane is a greenhouse gas, so as more methane thaws, the climate warms even more. This results in a feedback loop where the more the climate thaws, the more methane is released, the more the climate warms, and so on.

The vast majority of feedback systems are negative, while blood clotting is one of the few positive feedback systems. In positive feedback, the action caused by a stimulus actually enhances itself, rather than being reduced. Blood clots form this way when a blood vessel is damaged. First, platelets start to bind to the injury. Then the platelets begin releasing chemicals that recruit even more platelets to the area to form a clot. Another example of positive feedback is the contraction of the uterus via oxytocin during childbirth.

The only example of a positive feedback loop is labor contractions, since in that case, the output increases the original stimulus. In all of the other answer choices, the body is trying to maintain homeostasis by reversing the effect of the original stimulus.