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IB Biology 2025 · Theme D · Continuity and change

D3.3 Homeostasis. Practice questions with markscheme.

63 original IB-style questions on D3.3, written from the 2025 guide: 30 multiple-choice, 25 short-answer, 4 data-based, 2 extended-response parts, 1 labelling, 1 drawing. Below are two ready-made practice papers built from them, one at standard level (21 marks) and one at higher level (22 marks); switch between them above the paper. Hand one out as a class quiz or homework, or sit it yourself and mark against the scheme. Print it, project it, or build a fresh one on the same topic.

What the guide asks for

6 statements at SL and HL, 5 additional higher level.

  1. D3.3.1SL / HL Homeostasis as maintenance of the internal environment of an organism
  2. D3.3.2SL / HL Negative feedback loops in homeostasis
  3. D3.3.3SL / HL Regulation of blood glucose as an example of the role of hormones in homeostasis
  4. D3.3.4SL / HL Physiological changes that form the basis of type 1 and type 2 diabetes
  5. D3.3.5SL / HL Thermoregulation as an example of negative feedback control
  6. D3.3.6SL / HL Thermoregulation mechanisms in humans
  7. D3.3.7HL Role of the kidney in osmoregulation and excretion
  8. D3.3.8HL Role of the glomerulus, Bowman’s capsule and proximal convoluted tubule in excretion
  9. D3.3.9HL Role of the loop of Henle
  10. D3.3.10HL Osmoregulation by water reabsorption in the collecting ducts
  11. D3.3.11HL Changes in blood supply to organs in response to changes in activity

In the bank for D3.3

  • 30 multiple-choice
  • 25 short-answer
  • 4 data-based
  • 2 extended-response parts
  • 1 labelling
  • 1 drawing
  • 23 higher level only

Every question is original and tagged to a guide statement. See the whole bank →

Make your own

The practice paper

21 marks at SL · 22 at HL · each has its own code
Take it online → Build a fresh paper Paper code BbB-EAAAAAAAEBQAO8xC
Biology · topic quiz
Standard level · topic practice, not an exam format
30 minutes21 marks

Paper code: this paper was generated, so the code is its recipe. Enter it at biologybybradford.com/exam-maker to rebuild this exact paper and its markscheme.

Covers D3.3 Homeostasis · SL
Name:
1.

Lizards bask on warm rocks in the morning and retreat to shade at midday. What does this behaviour show?

[1]
  1. Shivering to generate heat
  2. Lizards are true endotherms
  3. Homeostasis is impossible in reptiles
  4. Behavioural thermoregulation
2.

Which hormone raises the basal metabolic rate in prolonged cold conditions, increasing heat generation?

[1]
  1. Insulin
  2. Cortisol
  3. Thyroxin
  4. Melatonin
3.

What is homeostasis?

[1]
  1. Keeping internal conditions within preset limits despite external change
  2. Growth of the body to a genetically determined set size
  3. Activation of defence responses against internal infection
  4. Keeping every internal variable exactly constant throughout life
4.

In the late nineteenth and early twentieth centuries, physiologists investigated the cause of diabetes mellitus, in which blood glucose concentration stays high and glucose appears in the urine. The pancreas was already known to secrete digestive enzymes through a duct into the small intestine. When the pancreatic duct of a dog is tied off for several weeks, the enzyme-secreting tissue of that pancreas wastes away, but small clusters of other cells survive. The table summarises the kind of results obtained in experiments on dogs (the values are illustrative).

DogTreatmentBlood glucose / mmol dm⁻³Glucose in urine
Ino surgery (control)5.0absent
IIwhole pancreas removed16.5present
IIIpancreatic duct tied off, so pancreatic juice could not reach the intestine; pancreas left in place5.2absent
IVwhole pancreas removed, then an extract of a pancreas whose duct had been tied off weeks before was injected into a vein16.0 before the injection; 6.8 four hours after itpresent before; much less after
(a)Explain why the result for dog III was needed before the researchers could conclude that the pancreas lowers blood glucose by secreting a substance into the blood.[2]
(b)Deduce two conclusions about the glucose-lowering substance from the result for dog IV.[2]
(c)Explain why the results for dogs II and IV together are stronger evidence that the pancreas makes a glucose-lowering substance than the result for dog II alone.[2]
(d)Extracts made from whole, normal pancreases had mostly failed to lower blood glucose. Suggest why the extract given to dog IV worked.[2]
5.

During an infection, chemicals released by white blood cells act on the hypothalamus and change the set point for body temperature. The graph shows the set point and the core body temperature of a person over 16 hours.

P Q 0 2 4 6 8 10 12 14 16 36.5 37.0 37.5 38.0 38.5 39.0 39.5 time / h temperature / °C core body temperature set point in hypothalamus
(a)Explain the rise in core body temperature during period P.[3]
(b)Predict, with reasons, two responses of the body during period Q.[2]
(c)Using periods P and Q, explain why this control of body temperature is described as negative feedback.[1]
6.

Draw a flow diagram to show how a rise in core body temperature above the set point is corrected by negative feedback. Include the stimulus, the receptor, at least two responses, and the effect of the responses on the stimulus.

[4]

Original practice questions © Biology by Bradford · CC BY-NC-SA 4.0 · Not affiliated with or endorsed by the International Baccalaureate Organization.
Rebuild or edit this exact paper (and its markscheme): biologybybradford.com/exam-maker?code=BbB-EAAAAAAAEBQAO8xC

Show the markscheme

Markscheme BbB-EAAAAAAAEBQAO8xC

One mark per point; / separates alternative wording within a point, OR separates alternative answers, words in brackets are not required, underlined words are essential. OWTTE = or words to that effect.

1. D3.3.6 [1]
  • D: ectotherms regulate temperature largely by behaviour (basking, shade, orientation); endotherms generate heat metabolically;
2. D3.3.5 [1]
  • C: thyroxin (from the thyroid) raises the metabolic rate of most tissues; secretion increases in sustained cold, boosting heat production;
3. D3.3.1 [1]
  • A: regulated variables (e.g. blood glucose, core temperature, water balance) oscillate within tolerable ranges around set points, maintained by (negative) feedback;
4. D3.3.3
  • (a) [2 max]
    • removing the pancreas (dog II) also stops pancreatic juice / digestive enzymes reaching the intestine, so the high blood glucose could have been caused by the loss of digestion (an alternative explanation);
    • dog III lost its pancreatic juice but kept a normal blood glucose / no glucose in its urine, so loss of the juice is not the cause and the alternative explanation is rejected;
    • (so) the pancreas must affect blood glucose by another route, such as a secretion into the blood, OWTTE;
    • dog III also had surgery, so the operation itself does not raise blood glucose (a control for the surgery), OWTTE;
  • (b) [2 max]
    • it acts when injected into the blood, so it is carried in the blood to its target cells / it is a hormone and does not need the duct;
    • it is made by the cells that survive when the duct is tied, not by the enzyme-secreting cells / it is made by endocrine cells of the pancreas;
    • it can replace the missing pancreas in lowering blood glucose / its absence caused the high glucose in dog II, OWTTE;

    Mark the first two conclusions only.

  • (c) [2 max]
    • removing the pancreas has many effects (loss of digestive enzymes, damage to nearby organs or blood vessels, stress of surgery), so dog II alone cannot show which loss raised the blood glucose / shows only a correlation;
    • in dog IV adding back only a pancreatic extract lowered blood glucose again, so the missing factor is a substance made in the pancreas;
    • removal shows the pancreas is needed and replacement shows the extract is enough (necessary and sufficient), OWTTE;
    • the hypothesis made a prediction (that an extract would restore control) that could have failed but did not, OWTTE;
  • (d) [2 max]
    • the glucose-lowering substance (insulin) is a protein;
    • the enzyme-secreting tissue of a normal pancreas contains protein-digesting enzymes / proteases, which digest the substance in the extract;
    • in the duct-tied pancreas the enzyme-secreting tissue had wasted away, so the substance stayed intact, OWTTE;

    Beyond this subtopic. Award if given; the marks above can be earned without it.

    • B1.1 proteases hydrolyse the peptide bonds of the protein into shorter peptides / amino acids;
5. D3.3.2
  • (a) [3 max]
    • the set point is raised to 39.0 °C, so the core temperature (37.0 °C) is now below the set point;
    • the hypothalamus detects the difference between the core temperature and the set point;
    • responses that generate heat / reduce heat loss are triggered, e.g. shivering / vasoconstriction of skin arterioles / hair erection / uncoupled respiration in brown adipose tissue;
    • core temperature rises until it reaches the new set point, when the responses stop, OWTTE;
  • (b) [2 max]
    • vasodilation of skin arterioles, so more heat is lost from the skin surface;
    • sweating, so heat is lost as the sweat evaporates;
    • shivering stops / less heat is generated by the muscles, OWTTE;

    Core temperature (39.0 °C) is now above the restored set point (37.0 °C). Mark the first two responses only; each needs its effect on heat loss or heat gain.

  • (c) [1 max]
    • in P the temperature is below the set point and is raised, and in Q it is above the set point and is lowered;
    • in each case the response opposes the deviation, returning the variable to the set point, OWTTE;
6. D3.3.2, D3.3.5 [4 max]
  • stimulus shown as core temperature rising above the set point (approximately 37 °C);
  • receptor shown as thermoreceptors in the hypothalamus (accept skin thermoreceptors as an additional input);
  • two correct responses shown, e.g. vasodilation of skin arterioles, sweating (evaporation of sweat), reduced shivering / lowered metabolic rate;
  • responses shown lowering core temperature back towards the set point;
  • an arrow from the response back to the stimulus, labelled to show the response removes / reverses the stimulus (negative feedback);

Accept boxes and arrows in any layout. Do not credit responses to cooling (shivering, vasoconstriction) as answers to a rise in temperature.

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