High School Biology : Introductory Topics

Study concepts, example questions & explanations for High School Biology

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Example Questions

Example Question #3 : Feedback And Homeostasis

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

Possible Answers:

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 that there is too little of a protein within a cell and activates 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 #1 : Feedback And Homeostasis

Which of the following is an example of negative feedback?

Possible Answers:

Ovulation via the luteinizing hormone (LH) surge

Thermoregulation via sweating

Childbirth contractions via oxytocin release

Blood clotting via fibrin action

Lactation via prolactin production

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 #2 : 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:

catabolism

negative feedback

vasoconstriction

reabsorption

osmosis

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 #2 : Feedback And Homeostasis

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.

Example Question #1 : Feedback And Homeostasis

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

Possible Answers:

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

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 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

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

Possible Answers:

equilibrium

negative feedback

positive feedback

feedback inhibition

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 #1 : Understanding Positive Feedback

Which of the following is an example of positive feedback?

Possible Answers:

Hunger causes metabolism to slow down, which reduces hunger

Oxytocin causes uterine contractions, which cause more release of oxytocin

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

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

Blood pressure rises, which causes vasodilation to lower blood pressure

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:

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.

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