Edexcel iGCSE Biology-3.31 Homeostasis- Study Notes- New Syllabus
Edexcel iGCSE Biology-3.31 Homeostasis- Study Notes- New syllabus
Edexcel iGCSE Biology-3.31 Homeostasis- Study Notes -Edexcel iGCSE Biology – per latest Syllabus.
Key Concepts:
3.31 understand that homeostasis is the maintenance of a constant internal environment, and that body water content and body temperature are both examples of homeostasis
Homeostasis
🌱 Introduction
Homeostasis → The maintenance of a constant internal environment, even when external conditions change.
It keeps the body in balance so that enzymes and cells can work efficiently.
🔹 Key Features of Homeostasis
- Stable internal conditions (despite external changes).
- Uses negative feedback → when a change happens, the body brings conditions back to normal.
- Maintains optimum conditions for:
- Enzyme action
- Cellular activities
🔹 Examples of Homeostasis
- Body Water Content
Controlled by the kidneys (via urine production).
Regulated by ADH (antidiuretic hormone):
– Too little water → more ADH → kidneys reabsorb more water → concentrated urine.
– Too much water → less ADH → kidneys reabsorb less water → dilute urine.
Ensures osmoregulation (balance of water and ions). - Body Temperature
Controlled by the hypothalamus in the brain.
Normal temp ≈ 37 °C (optimum for enzymes).
– If too hot → sweating, vasodilation (blood vessels widen).
– If too cold → shivering, vasoconstriction (blood vessels narrow), hairs stand up.
📊 Summary Table
| Factor Controlled | Organ/System Involved | Mechanism | Outcome |
|---|---|---|---|
| Water content | Kidneys, ADH | Control reabsorption of water in nephron | Balance of water + ions |
| Body temperature | Brain (hypothalamus), skin, blood vessels | Sweating, shivering, vasodilation/vasoconstriction | Enzymes kept at optimum 37 °C |
⚡ Quick Recap
Homeostasis = keeping internal environment stable.
Needed for enzymes + cells to function properly.
Examples:
Water balance → controlled by kidneys + ADH.
Temperature → controlled by hypothalamus + skin responses.
Works by negative feedback.
👉 Mnemonic: “HOT-W” → Homeostasis = Oxygen for enzymes, Temperature + Water regulation.