A Level Biology (A2) chapter 3: Homeostasis MCQs with answers
By Team Megalecture · Updated 4 Nov 2026
53 exam-style questions on 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. Glucose appears in the urine only when blood glucose concentration rises above a certain value. Why?
A
above this value, the glomerulus stops filtering glucose
B
above this value, the cotransporter proteins in the proximal tubule are saturated
C
above this value, glucose is actively secreted into the filtrate in the collecting duct
D
above this value, insulin prevents glucose from being reabsorbed
Show answer
Answer: B. Reabsorption depends on a limited number of cotransporter proteins. When the filtrate contains more glucose than they can carry, the excess stays in the tubule and passes into the urine.
2. Which feature distinguishes guard cells from most other cells of the lower epidermis?
A
guard cells have no cell wall at all
B
guard cells have no vacuole in their cytoplasm
C
guard cells contain chloroplasts
D
guard cells are dead, with lignified walls
Show answer
Answer: C. Guard cells have chloroplasts, whereas most other epidermal cells do not. They have living contents, a large vacuole and unevenly thickened cellulose walls.
3. After a meal rich in carbohydrate, blood glucose concentration rises. Which sequence follows?
A
α cells secrete glucagon → liver and muscle convert glucose to glycogen → blood glucose falls → more glucagon secreted
B
β cells secrete insulin → liver and muscle cells take up more glucose → blood glucose falls → more insulin secreted
C
β cells secrete insulin → liver cells break down their glycogen into glucose → blood glucose falls → less insulin secreted
D
β cells secrete insulin → liver and muscle store glucose as glycogen → blood glucose falls → less insulin secreted
Show answer
Answer: D. The rise is detected by β cells in the islets of Langerhans, which secrete insulin. Glucose uptake and glycogen synthesis lower blood glucose, and as it returns towards the set point less insulin is secreted: negative feedback.
4. How does a glucose biosensor differ from a glucose test strip?
A
it needs no enzyme, because glucose itself conducts electricity
B
it measures glucose only in urine samples, whereas test strips work only with blood
C
it converts the reaction into an electric current, giving a numerical reading
D
it uses peroxidase alone to release oxygen from glucose, which is then measured
Show answer
Answer: C. In a biosensor, the glucose oxidase reaction produces an electrical signal that a meter converts into a precise concentration. A test strip gives a colour that is matched to a chart, which is less precise.
5. What is meant by homeostasis?
A
the removal of the waste products of metabolism from the body, such as urea and carbon dioxide
B
keeping every body condition fixed at exactly one value at all times
C
keeping internal conditions within narrow limits despite internal or external changes
D
the response of an organism to a change in its external environment
Show answer
Answer: C. Homeostasis keeps conditions such as core temperature, blood glucose concentration and blood water potential within narrow limits around a set point; they fluctuate a little rather than staying fixed. Removing metabolic waste is excretion.
6. Which parts of a nephron are found mainly in the medulla of the kidney?
A
the glomerulus and the surrounding Bowman's capsule
B
the loop of Henle and the collecting duct
C
the proximal and distal convoluted tubules
D
the Bowman's capsule and proximal convoluted tubule
Show answer
Answer: B. The loops of Henle and collecting ducts run down into the medulla; the glomerulus, Bowman's capsule and both convoluted tubules are in the cortex.
7. Why do guard cells curve apart, opening the stoma, when they become turgid?
A
turgid guard cells shrink and pull away from each other
B
the cell wall on the outer side, away from the pore, is thicker than the inner wall
C
guard cells have no cell wall on the side next to the pore
D
the cell wall next to the pore is thicker and less stretchy than the outer wall
Show answer
Answer: D. The thick inner wall stretches less than the thin outer wall, and cellulose microfibrils running around the cells stop them getting wider, so as they swell they lengthen and bend apart.
8. Why does a glucose test strip react with glucose but not with other sugars such as fructose?
A
fructose is never present in blood or urine
B
peroxidase can only bind to glucose molecules
C
the chromogen changes colour only when a hexose sugar is present in the sample
D
glucose oxidase has an active site complementary in shape only to glucose
Show answer
Answer: D. Enzymes are specific: only glucose fits the active site of glucose oxidase, so only glucose leads to the formation of hydrogen peroxide and the colour change. Peroxidase acts on hydrogen peroxide, not on sugars.
9. How does insulin cause muscle cells to lower the blood glucose concentration?
A
glycogen is broken down, and the glucose is released into the blood
B
the membrane becomes less permeable to glucose, so fatty acids are respired instead
C
more GLUT4 proteins are placed in the cell surface membrane, and glucose is converted to glycogen
D
adenylyl cyclase is activated, forming cyclic AMP, which stimulates the breakdown of stored glycogen
Show answer
Answer: C. Insulin causes vesicles containing GLUT4 to fuse with the cell surface membrane, so more glucose enters by facilitated diffusion, and it stimulates glycogen synthesis. The adenylyl cyclase pathway is how glucagon acts on liver cells.
10. Which sequence occurs in guard cells when abscisic acid binds to its receptors?
A
Ca2+ enters cytoplasm → K+ leaves → water potential of guard cells rises → water leaves by osmosis
B
Ca2+ enters cytoplasm → K+ leaves → water potential of guard cells falls → water leaves by osmosis
C
Ca2+ leaves cytoplasm → K+ enters → water potential of guard cells falls → water enters by osmosis
D
K+ leaves → Ca2+ enters cytoplasm → water potential of guard cells rises → water enters by osmosis
Show answer
Answer: A. Loss of K+ makes the guard cell contents less concentrated, so their water potential rises above that of neighbouring cells. Water leaves by osmosis, the guard cells become flaccid and the stoma closes.
53, each with the answer and a short explanation, across 2 topics: Homeostasis in mammals, Homeostasis in plants. Every chapter test draws ten of them, so you can take it many times.
Is the A Level Biology (A2) chapter 3 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.
