A-Level Biology Topic 14: Homeostasis MCQs – 30 Practice Questions with Answers (Cambridge 9700)
Free practice for Cambridge International AS and A Level Biology 9700 on homeostasis in mammals and in plants, with every question followed by a short explanation to help you check your understanding.
Homeostasis and the Kidney
Q1. What is meant by homeostasis in mammals?
- (A) the maintenance of a stable internal environment within narrow limits
- (B) the maintenance of a constant external environment in a healthy adult under normal conditions
- (C) the control of body temperature only
- (D) the removal of all waste products at once
Show Answer
Answer: A – Homeostasis is the maintenance of a stable internal environment, keeping factors such as temperature and blood glucose within narrow limits.
Q2. In a negative feedback control system, what happens when a factor rises above its set point?
- (A) a response is triggered that pushes the factor even higher in a healthy adult under normal conditions
- (B) no response occurs until the factor falls on its own
- (C) the receptor stops detecting the factor permanently
- (D) a response is triggered that brings the factor back down towards the set point
Show Answer
Answer: D – Negative feedback corrects a deviation by triggering a response that reverses the change.
Q3. In homeostasis, which sequence correctly links the main components?
- (A) effector, stimulus, response, receptor, coordinator
- (B) stimulus, receptor, coordinator, effector, response
- (C) receptor, effector, stimulus, response, coordinator
- (D) stimulus, effector, coordinator, receptor, response
Show Answer
Answer: B – A stimulus is detected by a receptor, the information is coordinated, and an effector carries out the response.
Q4. Which two coordination systems are involved in homeostasis in mammals?
- (A) the digestive system and the respiratory system only
- (B) the skeletal system and the muscular system only
- (C) the nervous system and the endocrine system
- (D) the circulatory system alone
Show Answer
Answer: C – Homeostasis is coordinated by the nervous system and the endocrine system, acting on effectors such as muscles and glands.
Q5. Where is urea produced in the body?
- (A) in the kidney, from the filtration of blood plasma in a healthy adult under normal conditions
- (B) in the bladder, from the breakdown of glucose
- (C) in the pancreas, from the breakdown of fats
- (D) in the liver, from the deamination of excess amino acids
Show Answer
Answer: D – Urea is produced in the liver when excess amino acids are deaminated.
Q6. Which structure is the outer layer of the kidney?
- (A) the fibrous capsule
- (B) the renal pelvis in a healthy adult under normal conditions
- (C) the medulla
- (D) the cortex
Show Answer
Answer: A – The kidney is enclosed by the fibrous capsule, with the cortex beneath it and the medulla inside.
Q7. Which part of the kidney collects urine before it passes into the ureter?
- (A) the glomerulus
- (B) the loop of Henle
- (C) the renal pelvis
- (D) the distal convoluted tubule
Show Answer
Answer: C – Urine formed in the nephrons drains into the renal pelvis and then into the ureter.
Q8. Which blood vessel carries blood into the kidney for filtration?
- (A) a branch of the renal vein in a healthy adult under normal conditions
- (B) a branch of the renal artery
- (C) the hepatic portal vein
- (D) the pulmonary artery
Show Answer
Answer: B – Branches of the renal artery supply the kidney, and blood leaves by branches of the renal vein.
Q9. In the nephron, where does ultrafiltration take place?
- (A) in the Bowman capsule, around the glomerulus
- (B) in the collecting duct
- (C) in the loop of Henle
- (D) in the distal convoluted tubule in a healthy adult under normal conditions
Show Answer
Answer: A – Ultrafiltration in the Bowman capsule forms glomerular filtrate from blood in the glomerulus.
Q10. What drives ultrafiltration in the glomerulus?
- (A) active transport of water out of the Bowman capsule in a healthy adult under normal conditions
- (B) osmosis of large proteins into the tubule
- (C) diffusion of urea from the medulla into the blood
- (D) high blood pressure in the glomerular capillaries forcing small molecules out of the blood
Show Answer
Answer: D – High pressure in the glomerulus forces water, ions, glucose, amino acids and urea through the capillary walls into the Bowman capsule, while cells and large proteins remain in the blood.
Urine Formation and Osmoregulation
Q11. What is selective reabsorption in the proximal convoluted tubule?
- (A) the filtration of all substances out of the blood in a healthy adult under normal conditions
- (B) the secretion of glucose into the filtrate
- (C) the reabsorption of useful substances from the filtrate back into the blood
- (D) the storage of urea in the tubule wall
Show Answer
Answer: C – In the proximal convoluted tubule, useful substances such as glucose, amino acids, ions and much of the water are selectively reabsorbed.
Q12. How is glucose normally reabsorbed in the proximal convoluted tubule?
- (A) by simple diffusion through the tubule wall with no energy input in a healthy adult under normal conditions
- (B) by active transport and co-transport with sodium ions, using microvilli to increase surface area
- (C) by filtration back into the glomerulus
- (D) by osmosis directly into the collecting duct
Show Answer
Answer: B – The proximal convoluted tubule has microvilli and many mitochondria, suiting it for active reabsorption of glucose and other solutes.
Q13. Why does the Bowman capsule have a structure suited to ultrafiltration?
- (A) its wall is thick and muscular, so it can pump filtrate along in a healthy adult under normal conditions during normal activity in a typical mammal
- (B) it contains microvilli that absorb all the filtrate at once
- (C) it is lined with cilia that push blood into the tubule
- (D) its wall is thin and closely associated with the glomerular capillaries, with podocytes and a basement membrane acting as a filter
Show Answer
Answer: D – The thin wall, podocytes and basement membrane of the Bowman capsule allow small molecules to pass while holding back cells and large proteins.
Q14. Which hormone is involved in osmoregulation by acting on the collecting ducts?
- (A) antidiuretic hormone (ADH)
- (B) insulin
- (C) glucagon
- (D) adrenaline in a healthy adult under normal conditions
Show Answer
Answer: A – ADH, released from the posterior pituitary gland, increases the permeability of the collecting ducts to water.
Q15. When blood water potential falls, what happens to ADH release and water reabsorption?
- (A) ADH release falls, so less water is reabsorbed
- (B) ADH release increases, so more water is reabsorbed from the collecting ducts
- (C) ADH release increases, so less water is reabsorbed in a healthy adult under normal conditions
- (D) ADH has no effect on water reabsorption
Show Answer
Answer: B – A fall in blood water potential is detected by the hypothalamus, more ADH is released, and more water is reabsorbed, producing smaller volumes of more concentrated urine.
Q16. How does ADH increase water reabsorption in the collecting duct?
- (A) by blocking all aquaporins in the collecting duct
- (B) by increasing ultrafiltration in the glomerulus
- (C) by increasing the number of aquaporins in the collecting duct cell membranes
- (D) by preventing the reabsorption of glucose in the proximal tubule in a healthy adult under normal conditions
Show Answer
Answer: C – ADH causes aquaporins to be inserted into the membranes of collecting duct cells, allowing more water to leave the tubule by osmosis.
Q17. Which part of the brain detects changes in blood water potential and controls ADH release?
- (A) the hypothalamus
- (B) the cerebellum
- (C) the medulla oblongata
- (D) the cerebrum
Show Answer
Answer: A – Osmoreceptors in the hypothalamus detect blood water potential, and ADH is released from the posterior pituitary gland.
Q18. If a person drinks a large volume of water, what is the expected effect on urine output?
- (A) a smaller volume of more concentrated urine, because ADH release rises
- (B) no change in urine volume at all
- (C) a larger volume of more concentrated urine
- (D) a larger volume of more dilute urine, because ADH release falls
Show Answer
Answer: D – Extra water raises blood water potential, ADH release falls, less water is reabsorbed, and a larger volume of dilute urine is produced.
Q19. Which statement about the loop of Henle is correct?
- (A) it is the site of ultrafiltration in the nephron in a healthy adult under normal conditions during normal activity in a typical mammal
- (B) it helps to maintain a solute concentration gradient in the medulla, allowing water reabsorption from the collecting duct
- (C) it reabsorbs all the glucose from the filtrate
- (D) it secretes ADH into the blood
Show Answer
Answer: B – The loop of Henle contributes to the medullary gradient that allows water to be reabsorbed from the collecting duct when ADH is present.
Q20. A urine sample contains glucose. What does this most likely suggest, if the kidney tubules are working normally?
- (A) blood glucose concentration is unusually low in a healthy adult under normal conditions during normal activity in a typical mammal
- (B) ADH release is unusually high
- (C) blood glucose concentration has been so high that reabsorption could not remove all the glucose
- (D) ultrafiltration has stopped completely
Show Answer
Answer: C – Glucose is normally fully reabsorbed in the proximal convoluted tubule, so glucose in urine suggests blood glucose exceeded the reabsorption capacity, as in uncontrolled diabetes.
Blood Glucose Control and Plant Homeostasis
Q21. When blood glucose concentration rises after a meal, which hormone is released and what is its main effect on liver cells?
- (A) glucagon, which stimulates liver cells to convert glucose to glycogen
- (B) insulin, which stimulates liver cells to break down glycogen
- (C) ADH, which stimulates liver cells to release glucose
- (D) insulin, which stimulates liver cells to convert glucose to glycogen
Show Answer
Answer: D – Insulin promotes glycogenesis in liver cells and increases glucose uptake by muscle cells, lowering blood glucose.
Q22. When blood glucose concentration falls, glucagon acts on liver cells to do what?
- (A) stimulate the breakdown of glycogen to glucose
- (B) stimulate the conversion of glucose to glycogen
- (C) inhibit all glucose release from the liver
- (D) convert glucose directly to urea
Show Answer
Answer: A – Glucagon stimulates glycogenolysis in the liver, releasing glucose into the blood.
Q23. In the cell signalling pathway for glucagon, what is the second messenger formed after adenylyl cyclase is activated?
- (A) ATP directly, with no intermediate
- (B) cyclic AMP (cAMP)
- (C) glucose 6-phosphate
- (D) calcium ions only, with no other messenger
Show Answer
Answer: B – Binding of glucagon to its cell surface receptor activates a G-protein, which stimulates adenylyl cyclase to form cyclic AMP.
Q24. Why does the glucagon signalling pathway amplify the original signal?
- (A) one hormone molecule binds to only one enzyme in total in a healthy adult under normal conditions
- (B) the receptor is destroyed after a single use
- (C) each activated enzyme activates many more enzymes in the cascade, by phosphorylation
- (D) cAMP inhibits every enzyme in the pathway
Show Answer
Answer: C – The enzyme cascade amplifies the signal because each step activates more enzymes than the last.
Q25. What is the final cellular response in the glucagon pathway described in the syllabus?
- (A) activation of the final enzyme in the pathway, catalysing the breakdown of glycogen
- (B) activation of an enzyme that builds glycogen from glucose
- (C) formation of new glucagon receptors on the cell surface
- (D) direct breakdown of glucose to carbon dioxide in the cytoplasm in a healthy adult under normal conditions
Show Answer
Answer: A – The cascade ends with activation of the enzyme that breaks down glycogen, releasing glucose.
Q26. How do glucose test strips and biosensors detect glucose, in outline?
- (A) ADH binds to glucose and changes colour directly
- (B) insulin on the strip breaks down glucose to urea
- (C) glucose is filtered through a membrane and weighed in a healthy adult under normal conditions during normal activity in a typical mammal as described for ordinary physiological conditions
- (D) glucose oxidase converts glucose and produces a product detected with the help of peroxidase, giving a signal related to glucose concentration
Show Answer
Answer: D – Test strips and biosensors use glucose oxidase, with peroxidase involved in producing a measurable signal proportional to glucose concentration.
Q27. Why must stomata balance carbon dioxide uptake against water loss?
- (A) closed stomata allow more carbon dioxide in than open stomata in a healthy adult under normal conditions during normal activity in a typical mammal
- (B) stomata only open at night, when no water is lost
- (C) open stomata allow carbon dioxide in by diffusion for photosynthesis, but also allow water out by transpiration
- (D) stomata take up water directly from the air
Show Answer
Answer: C – Stomatal aperture is regulated to balance the need for carbon dioxide uptake with the need to minimise water loss.
Q28. How do guard cells open a stoma?
- (A) they lose water, become flaccid, and are pulled apart in a healthy adult under normal conditions during normal activity in a typical mammal
- (B) they take up potassium ions and water, become turgid, and bend apart because of their unevenly thickened walls
- (C) they divide to form a wider pore
- (D) they secrete wax that forces the pore open
Show Answer
Answer: B – When guard cells become turgid they change shape and the pore between them opens.
Q29. What is the role of abscisic acid during water stress in a plant?
- (A) it promotes stomatal opening at all times
- (B) it prevents guard cells from responding to light in a healthy adult under normal conditions
- (C) it increases water uptake by the roots only
- (D) it promotes stomatal closure, with calcium ions acting as a second messenger
Show Answer
Answer: D – Abscisic acid, produced during water stress, triggers stomatal closure, involving calcium ions as a second messenger.
Q30. Stomata show daily rhythms of opening and closing. What is the usual pattern in most plants?
- (A) they tend to open during the day, when light is available for photosynthesis, and close at night
- (B) they open only at midnight and close at dawn
- (C) they remain open continuously, day and night
- (D) they close during the day and open only at night in all conditions in a healthy adult under normal conditions
Show Answer
Answer: A – Daily rhythms generally link stomatal opening to daylight, when photosynthesis needs carbon dioxide, though water stress can override this.
Work through any questions you missed again, then revise those areas before moving on to the next topic.