MDCAT Biology chapter 15: Biology · Homeostasis MCQs with answers
By Team Megalecture · Updated 4 Nov 2026
35 exam-style questions on Biology · Homeostasis, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.
Try each one, then open the answer. These ten stay the same; the test draws new ones every time.
1. A man drinks little water and eats a lot of spinach, which is rich in oxalate. An overactive parathyroid gland also keeps his blood calcium high. Kidney stones form. They are most likely made of
A
cholesterol crystals
B
calcium oxalate
C
urea crystals
D
bile pigments
Show answer
Answer: B. High blood calcium and dietary oxalate, with too little water to keep them dissolved, give crystals of calcium oxalate, the commonest kind of kidney stone. Cholesterol and bile pigments form gallstones, and urea is far too soluble to crystallise.
2. When a mammal is cold, the erector muscles in its skin contract and its hairs stand on end. This reduces heat loss mainly because
A
the contracting erector muscles release most of the extra heat needed
B
the raised hairs squeeze the skin capillaries, so less blood reaches the surface
C
a thicker layer of still air, a poor conductor of heat, is trapped next to the skin
D
the raised hairs close the sweat pores, so that no sweat can evaporate
Show answer
Answer: C. Air trapped among raised hairs is a poor conductor, so it insulates the skin; in humans, with little body hair, the response only gives goose pimples. Whales, which have almost no hair, rely instead on a thick layer of blubber, a fat that also conducts heat poorly.
3. Fresh dialysis fluid contains glucose and salts at the concentrations found in normal plasma, but no urea. During haemodialysis, which of these passes from the blood into the fluid?
A
glucose
B
red blood cells
C
plasma proteins
D
urea
Show answer
Answer: D. Urea diffuses out down its concentration gradient because the fluid contains none. Glucose is at equal concentrations on both sides, so there is no net loss, and proteins and cells are too large to cross the membrane.
4. After severe blood loss a patient's blood pressure falls sharply and very little urine is formed. The main reason is that
A
less fluid is forced out of the glomerulus into Bowman's capsule
B
more plasma proteins pass into the filtrate and block the tubules
C
the loop of Henle reabsorbs all the filtrate into the blood
D
the collecting ducts stop reabsorbing water from the filtrate
Show answer
Answer: A. Ultrafiltration is driven by the blood pressure in the glomerular capillaries; when it falls, less filtrate forms, so less urine is made. Reabsorbing less water would increase the urine volume, not reduce it.
5. When a cold person shivers, most of the extra heat is produced by
A
fat under the skin
B
the skin capillaries
C
skeletal muscles
D
the sweat glands
Show answer
Answer: C. Shivering is rapid, involuntary contraction of skeletal muscles; the extra respiration that powers it releases heat. Fat under the skin reduces heat loss as an insulator but does not shiver.
6. Dogs have few sweat glands in their skin. On a hot day they lose heat mainly by
A
panting, which evaporates water from the mouth
B
narrowing the arterioles that supply the skin
C
shivering, so that their muscles release more heat
D
raising their fur to trap a layer of warm air
Show answer
Answer: A. Rapid shallow breathing (panting) passes air over the moist tongue and airways, and evaporation of water there takes away latent heat. Raised fur, vasoconstriction and shivering are responses that conserve or produce heat.
7. The ascending limb of the loop of Henle
A
reabsorbs all the glucose and amino acids from the filtrate
B
is permeable to water and reabsorbs most of the glucose
C
moves salts out to the medulla but is impermeable to water
D
is the part of the nephron where ultrafiltration occurs
Show answer
Answer: C. Salt leaving the water-tight ascending limb builds up a high solute concentration in the medulla; water can then be drawn out of the collecting ducts by osmosis to make concentrated urine. Glucose is reabsorbed in the proximal tubule.
8. At the start of a fever, a patient shivers and feels cold even though her body temperature is already rising. This is because
A
the thyroid has stopped secreting thyroxine, so the metabolic rate has fallen
B
pyrogens have raised the set point of the hypothalamus above the body temperature
C
pyrogens have lowered the set point of the hypothalamus below the body temperature
D
the skin arterioles have dilated, so heat is being lost faster than it is made
Show answer
Answer: B. Pyrogens released during infection reset the hypothalamic thermostat to a higher value; until the body reaches it, the body is "too cold" for the new set point, so heat-gain responses such as shivering and vasoconstriction occur.
9. Which statement about the two arterioles of a glomerulus is correct?
A
the efferent arteriole brings blood in and is wider than the afferent
B
the afferent arteriole carries blood away and is narrower than the efferent
C
the afferent arteriole brings blood in and is wider than the efferent
D
both arterioles have the same width, so the pressure stays low
Show answer
Answer: C. Blood enters the glomerulus by the wider afferent arteriole and leaves by the narrower efferent arteriole; this raises the pressure in the glomerular capillaries and drives ultrafiltration.
10. After a long walk on a hot day without drinking, a person passes a small volume of dark, concentrated urine. This is because
A
less ADH is secreted, so the glomerulus filters more water
B
more ADH is secreted, so the collecting ducts reabsorb more water
C
more ADH is secreted, so the collecting ducts reabsorb less water
D
less ADH is secreted, so the collecting ducts reabsorb more water
Show answer
Answer: B. Water loss raises the solute concentration of the blood; the hypothalamus detects this and more ADH is released from the posterior pituitary, making the collecting ducts more permeable so more water returns to the blood.
35, each with the answer and a short explanation, across 2 topics: Osmoregulation and the kidney, Thermoregulation and excretion. Every chapter test draws ten of them, so you can take it many times.
Is the MDCAT Biology chapter 15 test free?
Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.
How is the chapter test marked?
The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.
