High School Biology : Understanding Positive Feedback

Study concepts, example questions & explanations for High School Biology

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Example Questions

Example Question #2 : Feedback And Homeostasis

The increased release of oxytocin during childbirth is an example of __________.

Possible Answers:

feedback inhibition

negative feedback

equilibrium

positive feedback

Correct answer:

positive feedback

Explanation:

When production of a product in a system then causes more of the same product to be created it is known as positive feedback. In cotrast, when the production of product in a system inhibits additional product production it is known as negative feedback. Positive feedback leads to an exponential increase in the product, without any mediation. Negative feedback holds the product level at an equilibrium amount that is tightly regulated.

As oxytocin is released from the brain during childbirth uterine tension is increased, which further increases the amount of oxytocin created. As oxytocin is released, it stimulates the production of even more oxytocin, consistent with positive feedback.

Oxytocin is one of only very few positive feedback examples in biological systems. Almost all biological compounds are regulated via negative feedback.

Example Question #3 : Feedback And Homeostasis

Which of the following is an example of positive feedback?

Possible Answers:

Blood sugar rises, which causes the body to release insulin, which lowers blood sugar

Oxytocin causes uterine contractions, which cause more release of oxytocin

Blood pressure rises, which causes vasodilation to lower blood pressure

Hunger causes metabolism to slow down, which reduces hunger

Body temperature rises and causes sweat glands to open up and reduce body temperature

Correct answer:

Oxytocin causes uterine contractions, which cause more release of oxytocin

Explanation:

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.

Example Question #1 : Understanding Positive Feedback

The control of which of the following hormones is regulated by positive feedback?

Possible Answers:

Antidiuretic hormone

Calcitonin

Glucagon

Insulin

Oxytocin

Correct answer:

Oxytocin

Explanation:

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.

Example Question #2 : Understanding Positive Feedback

Which of the following is an example of a positive feedback loop? 

Possible Answers:

A species of plant goes extinct, and over time, another species of plant adapts to fill the extinct plant's ecological niche.

A warming climate thaws out frozen methane (a greenhouse gas) in Siberia, leading to further warming.

Plant and animal life slowly return to the slopes of a volcano following an eruption.

Invasive species are introduced to the Great Lakes via boat hulls, making it more difficult for native species to find enough food.

Correct answer:

A warming climate thaws out frozen methane (a greenhouse gas) in Siberia, leading to further warming.

Explanation:

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.

Example Question #3 : Understanding Positive Feedback

Which of the following is an example of positive feedback?

Possible Answers:

Blood clotting

Blood sugar levels

Thermoregulation

Blood osmolarity

Blood pressure

Correct answer:

Blood clotting

Explanation:

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.

Example Question #4 : Understanding Positive Feedback

Which of the following is an example of positive feedback?

Possible Answers:

Labor contractions cause the release of oxytocin, which stimulates more contractions

Low blood volume leads to the release of aldosterone, a hormone that causes sodium and water reabsorption to increase the blood volume 

Rise in blood glucose causes insulin secretion, which causes cellular uptake of glucose

Hot temperature causes the blood vessels in the skin to dilate and sweat glands secrete sweat to decrease the body's temperature back to normal 

The adrenocorticotropic hormone, released from the anterior pituitary, causes the release of cortisol from the adrenal glands, which inhibits the anterior pituitary from releasing more adrenocorticotropic hormone 

Correct answer:

Labor contractions cause the release of oxytocin, which stimulates more contractions

Explanation:

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. 

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