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
2025-2027 syllabus, in our words · A2 LevelWhat the syllabus expects you to be able to do in this topic, in plain English. For the exact wording, see the official syllabus (PDF).
- Explain the meaning of homeostasis and why it is important in mammals.
- Explain how homeostasis works in principle, in terms of: stimuli from inside and outside the body, receptors, the two coordination systems (the endocrine system and the nervous system), effectors (glands and muscles) and negative feedback.
- State that the liver makes urea by deaminating excess amino acids.
- Describe how the human kidney is structured, covering only: the cortex, the medulla, the renal pelvis, the fibrous capsule, the ureter, and the branches of the renal vein and renal artery.
- Identify the parts of a nephron, and the blood vessels and other structures linked to it, in electron micrographs, photomicrographs and diagrams, limited to: the glomerulus, Bowman's capsule, the loop of Henle, the collecting duct, and the proximal and distal convoluted tubules.
- Describe and explain how urine is formed in the nephron, covering only two processes: ultrafiltration of blood from the glomerulus into the Bowman's capsule, forming glomerular filtrate; and selective reabsorption in the proximal convoluted tubule.
- Relate the fine structure of the proximal convoluted tubule and of the Bowman's capsule to the jobs they do in forming urine.
- Describe the part each of these plays in osmoregulation: antidiuretic hormone (ADH), the hypothalamus, aquaporins, the posterior pituitary gland and the collecting ducts.
- Describe the principles behind cell signalling, using glucagon's control of blood glucose concentration as the example, limited to these steps: glucagon binds to a cell surface receptor, which changes shape (conformation); a G-protein is activated, which stimulates adenylyl cyclase; cyclic AMP (cAMP) forms as the second messenger; cAMP activates protein kinase A, starting an enzyme cascade; the cascade amplifies the signal as phosphorylation activates more and more enzymes; the response is activation of the last enzyme in the pathway, which catalyses glycogen breakdown.
- Explain how blood glucose concentration is regulated by negative feedback, referring to how insulin acts on liver and muscle cells and how glucagon acts on liver cells.
- Explain the principles by which test strips and biosensors measure glucose concentration in urine and blood, referring to the enzymes glucose oxidase and peroxidase.
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.
- › Podocytes form the inner lining of the Bowman's capsule and wrap around the glomerular capillaries, leaving gaps that filtrate passes through.
- › 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 inner wall of the Bowman's capsule is made of podocytes, whose foot-like processes leave filtration slits. Together with the gaps (fenestrations) in the glomerular capillary endothelium and the basement membrane between them, which acts as the main filter, this lets water and small solutes through quickly but holds back blood cells and large proteins.
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.
Review the material
Read full revision notes on Homeostasis in mammals — definitions, equations, common mistakes, and exam tips.
Read NotesMore 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.
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