High School Biology : Feedback and Homeostasis

Study concepts, example questions & explanations for High School Biology

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Example Questions

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Example Question #1 : Understanding Positive Feedback

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

Possible Answers:

Oxytocin

Glucagon

Calcitonin

Insulin

Antidiuretic hormone

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 #1 : Understanding Positive Feedback

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

Possible Answers:

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

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

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

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

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 #1 : Understanding Positive Feedback

Which of the following is an example of positive feedback?

Possible Answers:

Blood clotting

Blood osmolarity

Blood sugar levels

Blood pressure

Thermoregulation

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 #1 : Understanding Positive Feedback

Which of the following is an example of positive feedback?

Possible Answers:

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 

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

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

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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