High School Biology : Understanding Negative Feedback

Study concepts, example questions & explanations for High School Biology

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Example Questions

Example Question #2 : Feedback And Homeostasis

Which of the following is an example of negative feedback inhibition?

Possible Answers:

A cell senses that there is too little of a protein within a cell and activates transcription of the gene encoding the protein

A cells senses too little sugar in the blood and turns on transcription of the glucagon gene

A cell senses that the concentration of a protein is too high and represses transcription of the gene encoding the protein

A cell senses too much sugar in the blood and turns on transcription of the insulin gene

Correct answer:

A cell senses that the concentration of a protein is too high and represses transcription of the gene encoding the protein

Explanation:

Negative feedback inhibition occurs when "too much" of a substance results in decreased production of the same or a different substance. If having too much of a protein in a cell results in decreased transcription of the gene encoding the protein, then the protein was regulated by negative feedback. Another example (not listed here) would be the presence of too much sugar in the blood and repression of the glucagon gene to reduce production of sugar by other tissues.

While insulin and glucagon act in a negative feedback system, the question specifically asks for negative feedback inhibition. Turning on genes for insulin or glucagon would play a role in negative feedback, but would qualify as stimulation rather than inhibition.

Example Question #3 : Feedback And Homeostasis

Which of the following is an example of negative feedback?

Possible Answers:

Lactation via prolactin production

Thermoregulation via sweating

Ovulation via the luteinizing hormone (LH) surge

Blood clotting via fibrin action

Childbirth contractions via oxytocin release

Correct answer:

Thermoregulation via sweating

Explanation:

Homeostasis is the tendency of a system to maintain internal equilibrium. As such, negative feedback is a very important component of homeostasis because negative feedback loops are often self-regulating, and are usually very stable. Negative feedback processes result in reduction to change from equilibrium by inhibiting processes that deviate from equilibrium.

When body temperature rises, negative feedback through thermoregulation helps to cool the body back to equilibrium temperature. This is achieved through peripheral vasodilation, increased breathing rate, and sweating.

In contrast, positive feedback is when a process reinforces and amplifies deviations from equilibrium. The luteinizing hormone (LH) surge during ovulation and uterine contractions during child birth are rare examples of positive feedback in biology.

Example Question #4 : Feedback And Homeostasis

When the body needs to conserve water, antidiuretic hormone is secreted and the kidneys produce concentrated urine. This is an example of __________.

Possible Answers:

vasoconstriction

negative feedback

reabsorption

osmosis

catabolism

Correct answer:

negative feedback

Explanation:

Negative feedback reverses or shuts off a stimulus. When the body is experiencing dehydration, antidiuretic hormone is secreted, which works to decrease urine production, allowing the body to conserve fluids. When the body's fluids are replaced, negative feedback turns off antidiuretic hormone secretion. Catabolism is the breakdown of complex substances into simpler ones to release energy. Osmosis is the movement of water from an area of high concentration into an area of lower concentration. Vasoconstriction is a reduction in the diameter of a blood vessel. Antidiuretic hormone is also called vasopressin because it constricts blood vessels, which decreases urine output. Reabsorption is the taking back into the blood substances that had previously been filtered out from it. This occurs in the kidneys.

Example Question #4 : Understanding Negative Feedback

Which of the following processes is an example of negative feedback?

Possible Answers:

Breastfeeding

Blood clotting

Fever

Childbirth

Regulation of body temperature

Correct answer:

Regulation of body temperature

Explanation:

Negative feedback is the process of reestablishing a physiological set point. This is a corrective process. For example, during exercise, the body temperature increases. Negative feedback loops help bring the body temperature back down towards the set point of  by stimulating perspiration, dilating blood vessels to the extremities, etc. Positive feedback works in a way that exacerbates the effects of a stimulus. For example, during blood clotting, platelets bunch together in the area surrounding a wound. This causes more platelets to "get stuck" on the existing clump of platelets, causing further clotting.

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