IB Biology Quiz: Understand Homeostasis
16 questions · exam conditions
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Understand HomeostasisQuestion 1 of 16

In a hypothetical negative feedback loop, an increase in blood concentration of substance X stimulates gland Y to release hormone Z. Hormone Z acts on tissue W to decrease the production of substance X. In this homeostatic system, what is the role of tissue W?

The receptor that detects the initial stimulus.
The control centre that processes information.
The effector that carries out the response.
The feedback signal that communicates between components.
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IB Biology Quiz

IB Biology Quiz: Understand Homeostasis

Practice Understand Homeostasis in IB Biology with focused quiz questions that help you check what you know, review explanations, and build confidence with test-style prompts.

What this quiz covers

This quiz focuses on Understand Homeostasis, giving you a quick way to practice the rules, question types, and explanations that matter most for IB Biology.

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Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

All questions

Question 1

In a hypothetical negative feedback loop, an increase in blood concentration of substance X stimulates gland Y to release hormone Z. Hormone Z acts on tissue W to decrease the production of substance X. In this homeostatic system, what is the role of tissue W?

  1. The receptor that detects the initial stimulus.
  2. The control centre that processes information.
  3. The effector that carries out the response. (correct answer)
  4. The feedback signal that communicates between components.
Explanation: The effector is the part of the body (e.g., a tissue, muscle, or gland) that produces a response to a stimulus. In this case, tissue W is actively carrying out the response, which is to decrease the production of substance X, thereby correcting the initial change. Gland Y is the control centre, substance X is the variable being regulated, and hormone Z is the signal.

Question 2

After a carbohydrate-rich meal, insulin is released. Which statement accurately describes the subsequent events at the cellular level in muscle and adipose tissue?

  1. Insulin binds to receptors, triggering the fusion of vesicles containing GLUT4 transporters with the plasma membrane. (correct answer)
  2. Insulin directly enters the cells and binds to DNA to activate the genes for glycogen synthesis.
  3. Insulin binds to glucose molecules in the bloodstream, forming a complex that is transported into the cells.
  4. Insulin activates the sodium-potassium pump, which uses the sodium gradient to co-transport glucose into the cell.
Explanation: Insulin is a peptide hormone that binds to specific receptors on the surface of muscle and fat cells. This binding initiates a signal transduction cascade that causes vesicles containing the glucose transporter protein GLUT4 to move to and fuse with the plasma membrane. This increases the number of glucose transporters on the cell surface, facilitating the uptake of glucose from the blood. B is incorrect as insulin does not enter the cell. C is incorrect as insulin does not bind directly to glucose. D describes secondary active transport, which is not the primary mechanism of insulin-mediated glucose uptake in these tissues.

Question 3

Two individuals, P and Q, undergo a glucose tolerance test. Both have high fasting blood glucose. After consuming a glucose drink, individual P shows almost no increase in blood insulin levels from their low baseline. Individual Q shows a very high and sustained increase in blood insulin levels. Which diagnosis is most consistent with these results?

  1. P has Type II diabetes; Q has Type I diabetes.
  2. P has Type I diabetes; Q has Type II diabetes. (correct answer)
  3. Both P and Q have Type I diabetes, but Q's condition is more severe.
  4. Both P and Q have Type II diabetes, but P's pancreas has failed from exhaustion.
Explanation: Type I diabetes is characterized by the autoimmune destruction of pancreatic β-cells, leading to an inability to produce insulin. Individual P's lack of an insulin response to a glucose challenge is the hallmark of Type I. Type II diabetes is characterized by insulin resistance, where target cells do not respond effectively to insulin. The pancreas compensates by producing very high levels of insulin. Individual Q's high and sustained insulin level in the face of hyperglycemia indicates insulin resistance, which is characteristic of Type II.

Question 4

A rare genetic disorder results in non-functional ADH receptors on the collecting ducts of the kidneys. Which of the following would be a direct consequence of this condition in an individual who is dehydrated? (HL Only)

  1. The posterior pituitary would secrete abnormally low levels of ADH.
  2. The permeability of the collecting ducts to water would be very low. (correct answer)
  3. The individual would produce a small volume of highly concentrated urine.
  4. The ascending limb of the loop of Henle would stop actively transporting salts.
Explanation: ADH (antidiuretic hormone) functions by binding to receptors on the collecting ducts, which triggers the insertion of aquaporins and makes the ducts permeable to water. If these receptors are non-functional, the collecting ducts will remain impermeable to water, regardless of ADH levels. This leads to the production of large volumes of dilute urine, a condition known as nephrogenic diabetes insipidus. A is incorrect; dehydration would cause ADH levels to be very high. C is the opposite of what would occur. D is incorrect as ADH does not act on the ascending limb.

Question 5

Following a carbohydrate-rich meal, a strong insulin response causes a healthy person's blood glucose to dip slightly below the normal fasting level (reactive hypoglycemia). What is the most likely immediate hormonal response to correct this dip?

  1. Release of glucagon from pancreatic α-cells to stimulate liver glycogenolysis. (correct answer)
  2. A second, smaller release of insulin from pancreatic β-cells to stabilize glucose.
  3. Secretion of ADH from the posterior pituitary to increase water retention.
  4. Increased breakdown of muscle glycogen stimulated by adrenaline.
Explanation: The primary regulator of low blood glucose is the hormone glucagon, secreted by the α-cells of the pancreas. When blood glucose falls below the set point, glucagon is released. It travels to the liver and stimulates the breakdown of stored glycogen (glycogenolysis) into glucose, which is then released into the bloodstream, raising the blood glucose level back to normal. B would worsen the hypoglycemia. C is involved in water balance, not glucose regulation. D is a stress response, not the primary minute-to-minute regulator.

Question 6

A patient suffers a severe hemorrhage, leading to a significant drop in blood volume and blood pressure. This condition is a powerful stimulus for the release of which hormone to help restore water balance and pressure? (HL Only)

  1. ADH, to promote water retention. (correct answer)
  2. Glucagon, to mobilize energy stores.
  3. Insulin, to reduce cellular glucose uptake.
  4. Thyroxine, to increase metabolic rate.
Explanation: While ADH is primarily known for its role in osmoregulation, its release is also strongly stimulated by a large drop in blood pressure or volume, as occurs during a hemorrhage. In this context, it is often called vasopressin. It causes intense vasoconstriction of arterioles to increase blood pressure and, critically, it makes the kidney collecting ducts highly permeable to water, causing maximum water retention to help restore blood volume. The other hormones are not directly involved in this rapid response to blood loss.

Question 7

The hypothalamus secretes thyrotropin-releasing hormone (TRH), stimulating the pituitary to release thyroid-stimulating hormone (TSH). TSH stimulates the thyroid to produce thyroxine. High levels of thyroxine in the blood inhibit the secretion of TRH from the hypothalamus. Which component acts as the primary negative feedback signal in this pathway?

  1. The hypothalamus
  2. Thyrotropin-releasing hormone (TRH)
  3. Thyroid-stimulating hormone (TSH)
  4. Thyroxine (correct answer)
Explanation: In a negative feedback loop, the final product of a pathway inhibits an earlier step. In this endocrine axis, thyroxine is the final hormone produced. Its concentration in the blood is the variable being regulated. When thyroxine levels are high, it directly inhibits the hypothalamus (and pituitary), reducing the production of TRH (and TSH) and thus decreasing its own synthesis. Therefore, thyroxine is the negative feedback signal. A is the control center. B and C are intermediate stimulating hormones.

Question 8

In severe heat stroke, a person's core body temperature rises above 40°C. This extreme heat can increase the rate of metabolic reactions, which in turn generate more heat, causing the temperature to rise even further. This cycle represents:

  1. a successful acclimatization to a hot environment.
  2. a negative feedback loop with a higher set point.
  3. a failure of homeostasis leading to a positive feedback loop. (correct answer)
  4. a behavioral response to thermal stress.
Explanation: Homeostasis relies on negative feedback, where a change is counteracted by a response that reverses the change. In this case, the normal cooling mechanisms have failed. The stimulus (high temperature) is now causing a response (increased metabolic heat production) that amplifies the original stimulus. This is the definition of a positive feedback loop, which in this context is life-threatening and represents a complete breakdown of thermoregulation.

Question 9

A new drug is found to block the receptors on the smooth muscles of skin arterioles, preventing them from responding to signals from the hypothalamus. What would be a likely consequence for a person taking this drug if they are exposed to a cold environment?

  1. Their core body temperature would rise due to an uncontrolled increase in metabolic rate.
  2. They would be unable to sweat, leading to a risk of overheating even in the cold.
  3. They would lose heat more rapidly and shiver more intensely to compensate. (correct answer)
  4. Their skin would appear pale, and their core body temperature would remain stable.
Explanation: In a cold environment, the hypothalamus signals skin arterioles to constrict (vasoconstriction) to reduce blood flow to the skin and conserve heat. If this response is blocked, the arterioles will remain dilated, leading to excessive heat loss. The body's main compensatory mechanism for this failure is to increase heat production through more intense shivering. A is incorrect because core temperature would fall, not rise. B is incorrect because sweating is a cooling mechanism and is not related to arteriole constriction. D is incorrect because the skin would remain flushed (not pale), and the core temperature would be unstable.

Question 10

During a period of prolonged fasting (e.g., 24 hours), which process is primarily responsible for preventing a dangerous drop in blood glucose levels?

  1. Glucagon stimulates the breakdown of glycogen stores in skeletal muscle for release into the blood.
  2. The liver synthesizes glucose from non-carbohydrate sources like amino acids and glycerol. (correct answer)
  3. Insulin levels rise to promote the conversion of fatty acids to glucose in adipose tissue.
  4. The pancreas releases its own stored glucose directly into the bloodstream.
Explanation: After about 12-18 hours of fasting, the liver's glycogen stores are largely depleted. The primary mechanism to maintain blood glucose then becomes gluconeogenesis, the synthesis of new glucose from precursors like amino acids (from muscle protein breakdown) and glycerol (from fat breakdown), a process stimulated by glucagon. A is a common misconception; muscle glycogen is for local use only and cannot be released into the blood to raise blood glucose. C is incorrect as insulin levels are very low during fasting, and fatty acids cannot be converted to glucose in humans. D is incorrect as the pancreas regulates glucose but does not store and release it.

Question 11

Which action is a physiological, rather than a behavioral, response to a cold environment in mammals?

  1. Decreasing the rate of blood flow to the skin. (correct answer)
  2. Huddling with other individuals.
  3. Moving into a sunlit area.
  4. Reducing exposed surface area by curling up.
Explanation: Physiological responses are involuntary processes regulated by the body's internal systems. Decreasing blood flow to the skin (vasoconstriction) is an involuntary response controlled by the autonomic nervous system to conserve core body heat. Actions like moving to the sun, huddling, and curling up are all conscious, voluntary actions taken by the organism to modify its heat exchange with the environment, and are therefore classified as behavioral responses.

Question 12

After a person drinks 1.5 litres of pure water in a short time, what is the expected homeostatic response? (HL Only)

  1. Increased ADH secretion, leading to production of a small volume of concentrated urine.
  2. Decreased glomerular filtration rate to reduce the amount of water entering the nephrons.
  3. Increased glucagon secretion, leading to increased water generation from metabolism.
  4. Decreased ADH secretion, leading to production of a large volume of dilute urine. (correct answer)
Explanation: Drinking a large volume of water decreases the solute concentration of the blood (increases water potential). This is detected by osmoreceptors in the hypothalamus, which then signals the posterior pituitary to reduce ADH secretion. Lower ADH levels make the collecting ducts less permeable to water. As a result, less water is reabsorbed from the filtrate back into the blood, leading to the production of a large volume of dilute urine to excrete the excess water and restore normal blood osmolarity. A is the response to dehydration. C and D are incorrect mechanisms.

Question 13

An endothermic animal is moved from a warm environment (30°C) to a cold one (5°C). Which of the following represents a purely physiological, not behavioral, adjustment to maintain homeostasis?

  1. Finding a burrow to shelter from the wind.
  2. Orienting its body to minimize exposure to the cold air.
  3. Huddling together with other members of its species.
  4. Increasing metabolic heat production through non-shivering thermogenesis. (correct answer)
Explanation: Physiological adjustments are involuntary changes in body function. Non-shivering thermogenesis is a metabolic process where certain tissues, like brown adipose tissue, increase their metabolic rate specifically to produce heat. This is an involuntary, internal response. The other options (finding shelter, huddling, changing posture) are all conscious, voluntary actions, which are classified as behavioral adjustments.

Question 14

How does shivering contribute to thermoregulation?

  1. The friction between shivering muscle fibres generates thermal energy to warm the blood.
  2. It stimulates the hypothalamus to increase the body's metabolic set point to a higher temperature.
  3. It increases blood flow to the skin surface, allowing the body to absorb heat from the environment.
  4. The rapid, involuntary muscle contractions require ATP hydrolysis, releasing heat as a metabolic by-product. (correct answer)
Explanation: Shivering consists of rapid, involuntary contractions of skeletal muscles. Like all muscle contractions, this process is powered by the hydrolysis of ATP. The biochemical reactions involved in cellular respiration and ATP hydrolysis are not perfectly efficient; a significant portion of the energy from glucose and ATP is converted into thermal energy (heat). This metabolic heat production helps to raise or maintain core body temperature. A is incorrect; friction is a negligible source of heat. C is incorrect as vasoconstriction, not vasodilation, occurs in the cold. D misrepresents the control mechanism.

Question 15

An individual is lost in a hot desert without access to water. Which sequence correctly describes a key homeostatic response? (HL Only)

  1. Low blood volume → decreased ADH secretion → less permeable collecting duct → dilute urine.
  2. High blood solute concentration → stimulation of osmoreceptors → release of ADH → more permeable collecting duct. (correct answer)
  3. Low blood solute concentration → inhibition of hypothalamus → decreased ADH secretion → water retention.
  4. High blood pressure → stimulation of hypothalamus → release of ADH → water retention.
Explanation: Dehydration in a desert leads to water loss through sweat, increasing the solute concentration (osmolarity) of the blood. This change is detected by osmoreceptors in the hypothalamus. In response, the hypothalamus stimulates the posterior pituitary to release ADH. ADH increases the permeability of the kidney's collecting ducts to water, leading to increased water reabsorption and the production of a small volume of concentrated urine to conserve water. A and C describe responses to overhydration. D is incorrect as high blood pressure would inhibit, not stimulate, ADH release.

Question 16

Why does a person with untreated Type I diabetes often experience polyuria (excessive urination)? (HL Only)

  1. High blood glucose levels cause the glomerular filtration rate to increase dramatically.
  2. Lack of insulin inhibits the secretion of ADH, making the collecting ducts impermeable to water.
  3. High concentrations of glucose in the nephron filtrate reduce the osmotic potential for water reabsorption. (correct answer)
  4. The body attempts to excrete excess glucagon, which requires a large volume of water as a solvent.
Explanation: In untreated Type I diabetes, blood glucose levels are extremely high, exceeding the reabsorptive capacity of the proximal convoluted tubules. This results in a high concentration of glucose remaining in the filtrate. This glucose acts as an osmotic agent, increasing the solute potential of the fluid in the nephron. This reduces the osmotic gradient between the filtrate in the collecting duct and the medulla, impairing the ability of the kidneys to reabsorb water via osmosis, leading to a large output of urine.