Homeostasis in mammals
Cambridge A-Level Biology (9700) · Unit 14: Homeostasis · 20 flashcards
Homeostasis in mammals is topic 14.1 in the Cambridge A-Level Biology (9700) syllabus , positioned in Unit 14 — Homeostasis , alongside Homeostasis in plants. In one line: Homeostasis is the maintenance of a stable internal environment despite changes in external conditions. It is crucial for mammals because enzymes function optimally within narrow temperature and pH ranges, ensuring proper cell function and survival.
Marked as A2 Level: examined at A Level in Paper 4 (A Level Structured Questions) and Paper 5 (Planning, Analysis and Evaluation). It is not tested on the AS-only papers (Papers 1, 2 and 3).
The deck below contains 20 flashcards — 5 definitions and 15 key concepts — covering the precise wording mark schemes reward. Use the 5 definition cards to lock down command-word answers (define, state), then move on to the concept and calculation cards to handle explain, describe, calculate and compare questions.
Homeostasis and explain its importance in mammals
Homeostasis is the maintenance of a stable internal environment despite changes in external conditions. It is crucial for mammals because enzymes function optimally within narrow temperature and pH ranges, ensuring proper cell function and survival.
What the Cambridge 9700 syllabus says
Official 2025-2027 spec · A2 LevelThese are the exact learning outcomes Cambridge sets for this topic. The candidate is expected to be able to do each of these on the relevant paper.
- describe the principles of cell signalling using the example of the control of blood glucose concentration by glucagon, limited to: • binding of hormone to cell surface receptor causing conformational change • activation of G-protein leading to stimulation of adenylyl cyclase • formation of the second messenger, cyclic AMP (cAMP) • activation of protein kinase A by cAMP leading to initiation of an enzyme cascade • amplification of the signal through the enzyme cascade as a result of activation of more and more enzymes by phosphorylation • cellular response in which the final enzyme in the pathway is activated, catalysing the breakdown of glycogen
- explain how negative feedback control mechanisms regulate blood glucose concentration, with reference to the effects of insulin on muscle cells and liver cells and the effect of glucagon on liver cells
- explain the principles of operation of test strips and biosensors for measuring the concentration of glucose in blood and urine, with reference to glucose oxidase and peroxidase enzymes
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 9700 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Tips to avoid common mistakes in Homeostasis in mammals
- › In homeostasis questions, be specific about the exact site of hormone synthesis versus the site of release into the circulatory system.
- › Specify that podocytes are found in the squamous epithelium of the visceral layer of the Bowman's capsule.
- › Remember that the stoma is merely a pore; the physiological mechanism (receptors, ion movement) occurs in the guard cells.
- › Remember that an increase in blood water potential leads to a decrease in ADH secretion from the posterior pituitary gland.
Define homeostasis and explain its importance in mammals.
Homeostasis is the maintenance of a stable internal environment despite changes in external conditions. It is crucial for mammals because enzymes function optimally within narrow temperature and pH ranges, ensuring proper cell function and survival.
Describe the components involved in the homeostatic control mechanism.
Homeostasis involves internal/external stimuli, receptors (detect changes), a coordination system (nervous/endocrine), effectors (muscles/glands that bring about a response), and negative feedback (reverses the initial change).
What is the role of the liver in relation to urea production?
The liver produces urea from the deamination of excess amino acids. Deamination removes the amine group from amino acids, which is then converted to ammonia and subsequently to urea for excretion.
Outline the major structural components of the human kidney.
The kidney consists of the fibrous capsule, cortex (outer layer), medulla (inner layer), renal pelvis (collects urine), ureter (carries urine to bladder), and branches of the renal artery and renal vein (supply and drain blood).
Describe the key structures of a nephron and their associated blood vessels.
The nephron includes the glomerulus (capillary network), Bowman's capsule (surrounds glomerulus), proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting duct. These structures are associated with afferent and efferent arterioles and peritubular capillaries.
Explain the process of ultrafiltration in the Bowman's capsule.
Ultrafiltration occurs in the Bowman's capsule where high hydrostatic pressure forces water, ions, glucose, and amino acids out of the glomerulus capillaries and into the Bowman's capsule, forming glomerular filtrate. Blood cells and large proteins remain in the blood.
Describe the process of selective reabsorption in the proximal convoluted tubule.
Selective reabsorption occurs in the proximal convoluted tubule where useful substances like glucose, amino acids, ions, and water are reabsorbed from the glomerular filtrate back into the blood via active transport and osmosis.
How does the structure of the Bowman's capsule relate to its function?
The Bowman's capsule has a specialized structure with podocytes and fenestrations that allows for efficient ultrafiltration. Podocytes have foot-like processes that create filtration slits, preventing large molecules from entering the filtrate.
Explain the role of ADH in osmoregulation.
ADH (antidiuretic hormone), released by the posterior pituitary gland, increases the permeability of the collecting ducts to water. This allows more water to be reabsorbed back into the blood, resulting in a more concentrated urine and maintaining blood water potential.
Describe the role of aquaporins in osmoregulation.
Aquaporins are channel proteins in the collecting duct membranes that facilitate water reabsorption. ADH stimulates the insertion of more aquaporins into the collecting duct membrane, increasing water permeability and reabsorption.
Describe the first step in cell signalling by glucagon, leading to the breakdown of glycogen.
Glucagon binds to a specific receptor protein on the liver cell membrane. This binding causes a conformational change in the receptor, initiating the signalling cascade.
What is the role of the G-protein in glucagon-mediated cell signalling?
The activated receptor stimulates a G-protein. The G-protein activates adenylyl cyclase, an enzyme which converts ATP to cyclic AMP (cAMP).
Explain the function of cyclic AMP (cAMP) in the glucagon signalling pathway.
cAMP acts as a second messenger. It activates protein kinase A (PKA), which then initiates an enzyme cascade by phosphorylating other enzymes.
Describe the concept of signal amplification in the glucagon-stimulated glycogen breakdown pathway.
Signal amplification occurs through the enzyme cascade. Each activated enzyme phosphorylates and activates many more downstream enzymes, leading to a large overall effect.
How does insulin affect glucose uptake in muscle cells?
Insulin stimulates the insertion of GLUT4 glucose transporter proteins into the muscle cell membrane. This increases the permeability of the membrane to glucose, allowing more glucose to enter the cell.
Describe how insulin influences glucose metabolism in liver cells.
Insulin increases the rate of glycogenesis in liver cells. Glucose is converted to glycogen and stored, reducing blood glucose concentration.
Explain the effect of glucagon on liver cells regarding blood glucose concentration.
Glucagon stimulates glycogenolysis in liver cells, breaking down glycogen into glucose. It also promotes gluconeogenesis, synthesizing glucose from non-carbohydrate sources, both increasing blood glucose concentration.
Outline the principle of negative feedback in regulating blood glucose concentration.
When blood glucose is high, insulin is released, lowering blood glucose. When blood glucose is low, glucagon is released, raising blood glucose. These opposing actions maintain glucose within a narrow range.
Describe the role of glucose oxidase in a blood glucose test strip.
Glucose oxidase catalyses the oxidation of glucose to gluconic acid. This reaction produces hydrogen peroxide (H₂O₂), which is then detected.
Explain how peroxidase is used in a blood glucose test strip.
Peroxidase catalyses the reaction between hydrogen peroxide (produced by glucose oxidase) and a chromogen. The chromogen changes color, and the intensity of the color is proportional to the glucose concentration.
More topics in Unit 14 — Homeostasis
Homeostasis in mammals sits alongside these A-Level Biology decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
Key terms covered in this Homeostasis in mammals deck
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