Free Homeostasis questions for A Level Biology (9700), part of Energy & control. Each question has the answer and the marking points an examiner would look for.
Generate a full Homeostasis worksheet →All Energy & control questionsThe kidney regulates water content.
Explain how ADH increases water reabsorption in the collecting duct.
| Part | Answer and marking points | Marks |
|---|---|---|
| aquaporins inserted; more water reabsorbed by osmosis ADH binds receptors on collecting duct cells B1 vesicles containing aquaporins fuse with the membrane B1 more water reabsorbed by osmosis B1 | 3 |
Describe how the cells of the pancreas respond to a rise in blood glucose, and how the target cells respond.
Explain the role of cyclic AMP when glucagon binds to a liver cell.
Explain how the kidney produces dilute urine when a person drinks a large volume of water.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | β cells of islets detect rise; secrete insulin; binds receptors on liver/muscle cells; more GLUT4 in membranes, more glucose uptake; glycogenesis activated β cells in islets of Langerhans B1 insulin secreted into blood B1 binds receptors on target cells B1 increased glucose uptake via GLUT4 B1 glycogenesis B1 | 5 |
| (b) | glucagon binds receptor, activates G protein; adenylyl cyclase converts ATP to cAMP; cAMP activates protein kinase cascade; glycogen phosphorylase activated → glycogenolysis receptor and G protein B1 adenylyl cyclase makes cAMP B1 enzyme cascade amplifies signal B1 glycogen broken down to glucose B1 | 4 |
| (c) | osmoreceptors in hypothalamus detect higher water potential; less ADH released by posterior pituitary; fewer aquaporins in collecting duct, less water reabsorbed osmoreceptors in hypothalamus B1 less ADH B1 fewer aquaporins, less water reabsorbed B1 | 3 |
Fig. 3.1 is a diagram of a nephron.
Name the parts labelled A, C and E.
Explain how the loop of Henle creates a high solute concentration in the medulla.
Describe how the proximal convoluted tubule is adapted for selective reabsorption.
Name the hormone that controls water reabsorption and the gland that releases it.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | A glomerulus / Bowman’s capsule; C loop of Henle; E collecting duct A: Bowman’s capsule / renal capsule (allow glomerulus and Bowman’s capsule) B1 C: loop of Henle B1 E: collecting duct B1 | 3 |
| (b) | ascending limb impermeable to water, actively pumps Na⁺/Cl⁻ out; descending limb permeable to water; countercurrent multiplier; gradient increases towards tip the ascending limb actively transports Na⁺ and Cl⁻ out into the medulla B1 it is impermeable to water B1 water leaves the descending limb by osmosis B1 the countercurrent arrangement builds up a high solute concentration deep in the medulla B1 | 4 |
| (c) | microvilli large SA; many mitochondria for active transport; cotransporter proteins microvilli give a large surface area B1 many mitochondria provide ATP for active transport (Na⁺/K⁺ pumps) B1 cotransporter proteins reabsorb glucose and amino acids with Na⁺ B1 | 3 |
| (d) | ADH; posterior pituitary ADH B1 posterior pituitary gland B1 | 2 |
This question is about the control of stomatal aperture and water balance in plants.
Describe the structure of guard cells and how they open the stoma.
Explain why stomata usually open in light and close in darkness.
Explain how abscisic acid causes stomatal closure during drought.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | thick inner walls, cellulose microfibrils; K⁺ pumped in, water potential falls; water enters, turgid, bend apart guard cells have thicker inner walls and radially arranged cellulose microfibrils B1 H⁺ pumped out, K⁺ enter, lowering water potential B1 water enters by osmosis and the cells become turgid and bow apart B1 | 3 |
| (b) | CO₂ for photosynthesis in light; reduce water loss at night open in light to allow CO₂ in for photosynthesis B1 close at night when photosynthesis cannot occur, reducing water loss B1 | 2 |
| (c) | ABA receptors; Ca²⁺ second messenger; K⁺ out, water out, flaccid ABA binds receptors on guard cell membranes B1 Ca²⁺ enters, acting as a second messenger B1 K⁺ leaves, water potential rises, water leaves and guard cells become flaccid, closing the stoma B1 | 3 |
Blood glucose concentration is controlled by negative feedback.
Describe how glucagon raises blood glucose concentration, including the role of cAMP.
| Part | Answer and marking points | Marks |
|---|---|---|
| binds receptor; adenylyl cyclase; cAMP; enzyme cascade; glycogenolysis glucagon binds receptors on liver cells B1 activates adenylyl cyclase to make cAMP (second messenger) B1 cAMP activates an enzyme cascade B1 glycogen is broken down to glucose (glycogenolysis) B1 | 4 |
This question is about cell signalling.
Describe the stages of cell signalling by a hormone such as glucagon.
Explain why only certain cells respond to a particular hormone.
Explain the advantage of an enzyme cascade.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | hormone binds specific receptor; G protein activated; adenylyl cyclase makes cAMP; kinase cascade amplifies; response Any 4 of: glucagon binds to a specific receptor on the target cell membrane; this activates a G protein; adenylyl cyclase converts ATP to cyclic AMP (second messenger); cAMP activates protein kinases in a cascade that amplifies the signal; leading to the response (glycogen breakdown) B4 | 4 |
| (b) | only target cells have complementary receptors only target cells have receptors with a shape complementary to the hormone B2 | 2 |
| (c) | amplification; one hormone molecule activates many enzymes amplification: each activated enzyme activates many others, so one hormone molecule produces a large response quickly B2 | 2 |
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