📌Definition Table

Term	Definition
Homeostasis	Maintenance of a stable internal environment within narrow limits.
Negative feedback	A control mechanism that reverses changes and restores a set point.
Receptor	A sensor that detects changes in internal or external conditions.
Effector	A structure (muscle/gland) that produces a corrective response.
Set point	The optimal value around which a physiological factor is regulated.

📌Introduction

Homeostasis ensures that internal conditions remain constant despite external changes. This stability is critical for enzymes and cells to function optimally, maintaining temperature, pH, glucose, and osmotic balance. It operates through negative feedback systems, where deviations from a set point are detected and corrected. Without homeostasis, organisms would fail to survive in fluctuating environments

📌 Negative Feedback Mechanisms

• Most homeostatic controls use negative feedback to restore conditions.
• Involves a receptor, coordination system (nervous/endocrine), and effector.
• Example: increased blood glucose triggers insulin release to lower it.
• Positive feedback amplifies changes (e.g., oxytocin in childbirth), not used for stability.
• Ensures enzymes and metabolic processes remain within optimal ranges.

🧠 Examiner Tip: Be precise—negative feedback restores set points, while positive feedback amplifies changes; students often confuse the two.

📌 Physiological Factors Maintained

• Core body temperature (critical for enzyme activity).
• Blood pH (narrow range required for protein function).
• Glucose concentration (for cellular respiration).
• Osmotic balance of blood and tissues.
• Gas concentrations (O₂, CO₂) in some animals.

🧬 IA Tips & Guidance: Investigations can include how body temperature or heart rate changes with exercise, linking real data to negative feedback regulation.

📌 Coordination of Homeostasis

• Nervous system: fast, short-term responses (e.g., shivering, sweating).
• Endocrine system: slower, longer-term regulation (e.g., thyroxine, insulin).
• Organs work together, e.g., pancreas–liver in glucose control.
• Disruptions (e.g., diabetes, dehydration) show the importance of regulation.
• Homeostasis underpins survival in diverse environments.

🌐 EE Focus: An EE could compare efficiency of negative feedback in ectotherms vs endotherms, or investigate homeostatic disruptions in disease states.

📌 Applications in Biology

• Understanding feedback loops is essential in medicine (e.g., diabetes treatment).
• Artificial regulation: dialysis machines mimic kidney function.
• Athletic performance depends on thermoregulation and hydration control.
• Feedback models used in biotechnology and ecology.
• Explains adaptation to extreme environments.

❤️ CAS Link: Students can design workshops or models showing how feedback loops operate (e.g., thermostat analogy), teaching peers about balance in physiology.

📌 Integration with Other Systems

• Nervous and endocrine systems act in synergy.
• Feedback ensures survival under changing environments.
• Regulation applies across scales—from cells to ecosystems.
• Failures cause pathology, highlighting its importance.
• A foundation concept linking all physiology.

🔍 TOK Perspective: Homeostasis is inferred through indirect measures (temperature, glucose). TOK reflection: How reliable is indirect evidence in confirming biological processes?

📝 Paper 2: Expect to explain negative feedback with examples (glucose, temperature). Questions may require drawing labelled diagrams of loops or comparing negative vs positive feedback.