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3.6.4 Homeostasis

AQA A-level Biology 3.6.4 practice on Homeostasis, with free MCQs, clues and worked explanations drawn from the Organisms respond to changes in their internal and external environments section of specification 7402.

Specification route
3.6.4
Question bank
41 questions
Course stage
Year 13 / A-level only

Sample questions

QUESTION 1 · 3.6.4.1 · LEVEL 1

How is the principle of negative feedback defined in biological homeostasis?

  • A deviation from the normal optimum level triggers a corrective mechanism that restores the system to its original level.
  • A deviation from the normal optimum level is detected and further amplified to create a new physiological state.
  • The body actively prevents any changes from occurring in the internal environment whatsoever.
  • A decrease in a substance causes a permanent cessation of its production by the cells.
Show clue

If you get too hot, your body works to cool you down.

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Answer: A deviation from the normal optimum level triggers a corrective mechanism that restores the system to its original level.

Negative feedback restores systems to their original level. It involves a receptor detecting a deviation and an effector bringing about a response that reverses the deviation.

QUESTION 2 · 3.6.4.2 · LEVEL 4

When blood glucose concentration is too high, how does insulin act to lower it?

  • It binds to receptors on cell membranes, causing vesicles containing GLUT4 carrier proteins to fuse with the membrane, increasing glucose uptake.
  • It diffuses into the nucleus and alters the DNA to stop the production of glucose.
  • It binds directly to glucose molecules in the blood and transports them out via the kidneys.
  • It triggers the breakdown of glycogen into glucose inside liver cells.
Show clue

Insulin 'unlocks' the cells to let glucose inside.

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Answer: It binds to receptors on cell membranes, causing vesicles containing GLUT4 carrier proteins to fuse with the membrane, increasing glucose uptake.

The action of insulin. Insulin attaches to receptors on target cells, changing their tertiary structure and causing vesicles containing glucose transport proteins to fuse with the cell-surface membrane, drastically increasing permeability to glucose.

QUESTION 3 · 3.6.4.2 · LEVEL 2

What is the biological term for the formation of glucose from non-carbohydrate sources, such as amino acids or glycerol?

  • Gluconeogenesis
  • Glycogenolysis
  • Glycogenesis
  • Glycolysis
Show clue

Break down the word: 'gluco-' (glucose), '-neo-' (new), '-genesis' (creation).

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Answer: Gluconeogenesis

The roles of the liver in glycogenesis, glycogenolysis and gluconeogenesis. Gluconeogenesis is the creation of new glucose from non-carbohydrate sources, stimulated by glucagon.

QUESTION 4 · 3.6.4.2 · LEVEL 4

According to the second messenger model, what happens after adrenaline or glucagon binds to a transmembrane protein receptor on a liver cell?

  • The enzyme adenylate cyclase is activated, converting ATP into cyclic AMP (cAMP), which then activates protein kinase to convert glycogen to glucose.
  • The hormone physically enters the cell and acts as an enzyme to hydrolyse glycogen.
  • The receptor opens a massive channel that allows glucose to flood directly out of the cell.
  • The hormone triggers the cell to release insulin, which acts as the second messenger.
Show clue

The hormone is the 'first messenger'. It never enters the cell, but triggers a chemical reaction inside.

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Answer: The enzyme adenylate cyclase is activated, converting ATP into cyclic AMP (cAMP), which then activates protein kinase to convert glycogen to glucose.

The role of adrenaline in the second messenger model. Adrenaline/glucagon binds to a receptor, activating adenylate cyclase. This converts ATP to cAMP (the second messenger), which activates protein kinase, leading to glycogenolysis.

QUESTION 5 · 3.6.4.2 · LEVEL 2

What is the primary underlying cause of Type 2 diabetes?

  • Glycoprotein receptors on body cells lose their responsiveness to insulin, or an inadequate supply of insulin is produced.
  • The body's immune system completely destroys the $\beta$ cells in the islets of Langerhans.
  • A genetic mutation prevents the liver from storing any glycogen whatsoever.
  • The kidneys lose the ability to filter glucose out of the urine.
Show clue

Type 1 is generally an autoimmune lack of insulin. Type 2 is usually linked to obesity and a loss of receptor sensitivity.

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Answer: Glycoprotein receptors on body cells lose their responsiveness to insulin, or an inadequate supply of insulin is produced.

The causes of types I and II diabetes and their control. Type 1 is characterized by a lack of insulin production. Type 2 (usually acquired later in life) is characterized by a loss of receptor responsiveness to insulin.

QUESTION 6 · 3.6.4.3 · LEVEL 4

In the mammalian kidney, what is the primary function of the Loop of Henle acting as a counter-current multiplier?

  • To maintain a very low water potential (high sodium ion concentration) in the interstitial fluid of the medulla, allowing water reabsorption from the collecting duct.
  • To actively filter all large proteins and red blood cells out of the blood plasma.
  • To passively reabsorb all the glucose and amino acids from the glomerular filtrate.
  • To actively transport water molecules from the filtrate directly back into the bloodstream.
Show clue

The Loop plunges deep into the medulla to make it incredibly salty.

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Answer: To maintain a very low water potential (high sodium ion concentration) in the interstitial fluid of the medulla, allowing water reabsorption from the collecting duct.

The role of the loop of Henle in maintaining a sodium ion gradient. The ascending limb actively pumps out $Na^{+}$ and $Cl^{-}$ but is impermeable to water. This lowers the water potential of the medulla, so water can be drawn out of the collecting duct by osmosis.

QUESTION 7 · 3.6.4.3 · LEVEL 1

Where in the body are the osmoreceptors that monitor the water potential of the blood located?

  • Hypothalamus
  • Posterior pituitary gland
  • Medulla oblongata
  • Bowman's capsule
Show clue

This structure is in the brain and works closely with the pituitary gland.

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Answer: Hypothalamus

The roles of the hypothalamus, posterior pituitary and antidiuretic hormone (ADH) in osmoregulation. Osmoreceptors in the hypothalamus detect a fall in blood water potential (by shrinking) and stimulate the posterior pituitary to release ADH.

QUESTION 8 · 3.6.4.3 · LEVEL 3

How does Antidiuretic Hormone (ADH) act to increase the water potential of the blood?

  • It binds to receptors on the collecting duct and distal convoluted tubule, causing aquaporins to be inserted into the membrane, increasing water permeability.
  • It actively pumps water molecules out of the Loop of Henle and into the vasa recta.
  • It dilates the afferent arteriole to decrease the hydrostatic pressure in the glomerulus.
  • It stimulates the liver to rapidly break down glycogen, releasing water as a byproduct.
Show clue

ADH makes the walls of the final tubes in the kidney more 'leaky' to water.

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Answer: It binds to receptors on the collecting duct and distal convoluted tubule, causing aquaporins to be inserted into the membrane, increasing water permeability.

The action of ADH. ADH binds to receptors, triggering vesicles containing aquaporins (water channels) to fuse with the cell-surface membrane of the collecting duct. This increases permeability, so more water is reabsorbed by osmosis into the blood.

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