Homeostasis and Excretion IGCSE Biology: Complete Guide
Homeostasis and Excretion IGCSE Biology: Complete Guide
⚖️ Understanding Homeostasis in IGCSE Biology
Homeostasis maintains constant internal conditions. This guide covers temperature regulation, kidney function, and excretion processes.
🧠 Memory Tips
Homeostasis: “Constant Internal Conditions”
- Temperature: 37°C in humans
- Blood glucose: Controlled by insulin
- Water balance: Controlled by kidneys
- pH: Maintained around 7.4
Kidney Functions: “Filter Reabsorb Secrete”
- Filter: Remove waste from blood
- Reabsorb: Useful substances back to blood
- Secrete: Additional waste removal
Negative Feedback: “Detect Correct Return”
- Detect: Change from normal
- Correct: Take action
- Return: Back to normal level
📚 Key Concepts
What is Homeostasis?
- Definition: Maintaining constant internal environment
- Importance: Optimal conditions for enzymes
- Examples: Temperature, blood glucose, water balance
- Mechanism: Negative feedback
Temperature Regulation
- Normal: 37°C in humans
- Too hot: Sweating, vasodilation
- Too cold: Shivering, vasoconstriction
- Control center: Hypothalamus in brain
Excretion
- Definition: Removal of metabolic waste
- Main organs: Kidneys, lungs, skin, liver
- Waste products: Urea, CO₂, excess water
Kidney Structure
- Nephrons: Functional units
- Glomerulus: Filtration unit
- Tubules: Reabsorption and secretion
- Collecting duct: Final urine concentration
Kidney Function
- Filtration: Blood filtered at glomerulus
- Reabsorption: Useful substances returned
- Secretion: Additional waste removal
- Concentration: Final urine formation
🎯 IGCSE Exam Focus
Common Questions
- Explain negative feedback (5 marks)
- Describe kidney function (6 marks)
- Compare responses to hot/cold (4 marks)
- Analyze homeostasis graphs (4 marks)
Key Processes
- Ultrafiltration: High pressure filtration
- Selective reabsorption: Useful substances retained
- Osmoregulation: Water balance control
Temperature Control
- Hot conditions: Vasodilation, sweating, behavioral changes
- Cold conditions: Vasoconstriction, shivering, behavioral changes
🌡️ Temperature Regulation
Heat Gain Mechanisms
- Shivering: Muscle contractions generate heat
- Vasoconstriction: Reduce heat loss
- Behavioral: Warm clothing, shelter
- Metabolic: Increased cellular respiration
Heat Loss Mechanisms
- Sweating: Evaporation cools skin
- Vasodilation: Increase heat loss
- Behavioral: Light clothing, shade
- Panting: In some animals
Control Center
- Hypothalamus: Temperature control center
- Thermoreceptors: Detect temperature changes
- Effectors: Muscles, blood vessels, sweat glands
🫘 Kidney Function
Nephron Structure
- Bowman’s capsule: Surrounds glomerulus
- Proximal tubule: First reabsorption site
- Loop of Henle: Concentrates urine
- Distal tubule: Fine-tuning
- Collecting duct: Final concentration
Filtration Process
- High pressure: Forces filtration
- Small molecules: Pass through
- Large molecules: Proteins, cells remain
- Filtrate: Water, glucose, urea, salts
Reabsorption
- Glucose: 100% reabsorbed (normally)
- Water: Variable reabsorption
- Salts: Selective reabsorption
- Amino acids: Completely reabsorbed
💧 Water Balance
ADH (Antidiuretic Hormone)
- Source: Pituitary gland
- Function: Controls water reabsorption
- High ADH: More water reabsorbed, concentrated urine
- Low ADH: Less water reabsorbed, dilute urine
Osmoregulation
- Osmoreceptors: Detect blood concentration
- Feedback loop: ADH release controlled
- Dehydration: More ADH, less urine
- Overhydration: Less ADH, more urine
🩸 Blood Glucose Regulation
Normal Level
- Range: 80-120 mg/dL
- Importance: Brain fuel, cell energy
- Control: Insulin and glucagon
High Glucose
- Insulin released: From pancreas
- Glucose uptake: By cells
- Glycogen formation: In liver
- Blood glucose falls: Back to normal
Low Glucose
- Glucagon released: From pancreas
- Glycogen breakdown: In liver
- Glucose release: Into blood
- Blood glucose rises: Back to normal
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