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 Biological Equilibrium

Which of the following is true when the body is under homeostasis?

Possible Answers:

The body cannot generate its own heat in very cold conditions

The body is under dynamic equilibrium

The body is able to self-sustain without anything from the environment

The body is at an appropriate core temperature and no longer needs to regulate body temperature

The body stops digesting foods

Correct answer:

The body is under dynamic equilibrium

Explanation:

Homeostasis means "staying still" in Greek, and is a property of the human body that describes when functions and processes allow the conditions of the body to remain stable. This does not mean that the body ceases any function. It simply means that the current functions of the body are able to keep the body at a stable condition.

For example, blood glucose in the body is under homeostatic regulation by the hormones insulin and glucagon. Both hormones are always in circulation, meaning that glucose is both being released into the blood and begin taken from the blood for storage. The result is a stable amount of glucose because both processes occur together. When a meal causes blood glucose to rise, insulin levels increase and glucagon levels decrease to accommodate the change, but both hormones are still present. This creates a dynamic equilibrium in which glucose is both retained and released, allowing a stable amount to be in circulation.

Example Question #1 : Feedback And Homeostasis

Which of following correctly describes how a catalyst affects a chemical reaction?

Possible Answers:

Slows down a chemical reaction by increasing the activation energy

Speeds up a chemical reaction by increasing the activation energy

Speeds up a chemical reaction by lowering the activation energy

Slows down a chemical reaction by lowering the activation energy

Has no effect on the speed of the chemical reaction, but increases the amount of product produced

Correct answer:

Speeds up a chemical reaction by lowering the activation energy

Explanation:

A catalyst is a substance that increases the rate of a reaction by lowering the activation energy needed for the given chemical reaction to occur. Activation energy is the input of energy required for a reaction to occur. This energy is used to break the bonds of the reactant, allowing the reaction to proceed. If a catalyst lowers the amount of energy needed for a reaction to occur, the reaction can occur at a faster rate because it reaches that lower energy level more quickly than it would have the original higher energy level.

Example Question #1 : Feedback And Homeostasis

Which is not an example of homeostasis?

Possible Answers:

The kidneys work to remove excess salt, urea, and water from the bloodstream

Mitochondria create ATP through proton pumps in order to power the cellular processes

Oxygen content in the bloodstream is low, so the heart pumps faster and speed/depth of breathing increases

Insulin is released by the pancreas to encourage cells to retain their glucose instead of releasing it into the blood stream

Warm blooded (endothermic) animals sweat to release heat, or shiver to increase metabolic activity and increase body temperature

Correct answer:

Mitochondria create ATP through proton pumps in order to power the cellular processes

Explanation:

The situation describing ATP production is the only one in which there is no problem in need of correction. Homeostasis requires maintenance of a balance. While ATP production is an essential process, the simple function of the ATP synthase proton pump is not directly related to biological stability in homeostasis.

All other answers describe situations in which the body corrects a problem or situation and restores balance to internal mechanisms. This is the nature of homeostasis—there is a disruption to the balance, and the body adjusts in order to keep the processes running smoothly.

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.

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