IB MYP 4-5 Biology-Homeostasis- Study Notes - New Syllabus
IB MYP 4-5 Biology-Homeostasis- Study Notes – New syllabus
IB MYP 4-5 Biology-Homeostasis- Study Notes – IB MYP 4-5 Biology – per latest IB MYP Biology Syllabus.
Key Concepts:
- Negative feedback mechanisms
- Thermoregulation
- Blood glucose regulation
Negative Feedback Mechanisms
Definition:
Negative feedback is a biological process where the body detects a change from the normal condition (set point) and responds in a way that reverses or reduces that change.
Think of it like a thermostat: If a room gets too hot, the AC cools it down. If it’s too cold, the heater warms it up. The goal? Keep conditions stable.
Why is it Important?
Negative feedback helps the body maintain homeostasis – a stable internal environment – despite changes in the external environment.
Key Features of Negative Feedback:
| Component | Role |
|---|---|
| Stimulus | A change in internal environment (e.g. body temperature rises) |
| Receptor | Detects the change (e.g. skin or hypothalamus sensors) |
| Control Center | Processes information and decides what to do (usually the brain) |
| Effector | Carries out the response (e.g. sweat glands) |
| Response | Reverses the original change (e.g. cools the body down) |
Example 1: Body Temperature Regulation
- Stimulus: Body temp rises above 37°C
- Receptors: Skin temperature sensors detect the heat
- Control center: Hypothalamus in the brain
- Effectors: Sweat glands increase sweat production, blood vessels vasodilate
- Response: Heat is lost → body temperature returns to normal
Change is reduced → Normal body temp restored → Feedback stops
Example 2: Blood Glucose Regulation
- Stimulus: Blood glucose level increases
- Receptors: Pancreas detects the rise
- Effector: Pancreas releases insulin
- Response: Liver and muscles absorb glucose → blood glucose returns to normal
Negative feedback stops insulin production once levels normalize
Example 3: Blood Pressure Regulation
- Stimulus: Drop in BP (e.g., from standing up too quickly)
- Receptors: Baroreceptors in blood vessels
- Control center: Brainstem (medulla)
- Effectors: Heart beats faster, blood vessels vasoconstrict
- Response: BP increases → normal BP restored
Common Misconception:
Negative feedback doesn’t mean “bad” — it simply refers to reversing the change, not the quality of the outcome.
Summary:
Negative feedback = change → detected → corrected → back to normal.
This process is essential for keeping your body functioning properly and preventing damage from extreme conditions.
Key Terms to Remember:
- Homeostasis: Maintaining a stable internal environment
- Effector: Organ/tissue that acts to correct change
- Receptor: Sensor that detects change
- Vasodilation: Widening of blood vessels
- Vasoconstriction: Narrowing of blood vessels
- Insulin: Hormone that lowers blood glucose
Thermoregulation
What is Thermoregulation?
Thermoregulation is the process by which your body maintains a stable internal temperature, usually around 37°C, even when the environment changes. It’s a part of homeostasis and is controlled by the hypothalamus in the brain.
Why is It Important?
- Enzymes work best at 37°C
- If too hot – enzymes denature, risk of heatstroke
- If too cold – metabolism slows, risk of hypothermia
🧬 How It Works: The Negative Feedback Loop
| Step | What Happens |
|---|---|
| 1. Stimulus | Change in body temperature |
| 2. Receptor | Detected by skin and hypothalamus |
| 3. Control Center | Hypothalamus processes signal |
| 4. Effectors | Muscles, sweat glands, blood vessels |
| 5. Response | Body temperature returns to 37°C |
If the Body Gets TOO HOT:
- Triggers: Exercise, hot weather, fever
Responses:- Sweating increases → evaporation cools the body
- Vasodilation – blood vessels widen → more heat lost
- Body hairs lie flat
- Behavior: seek shade, drink water, remove clothing
If the Body Gets TOO COLD:
- Triggers: Cold air, swimming, low temperature
- Responses:
- Shivering – muscles contract to generate heat
- Vasoconstriction – blood vessels narrow to keep heat
- No sweating
- Body hairs stand up → trap insulating air
- Behavior: wear warm clothes, seek shelter
Summary:
| Condition | Response | Effect |
|---|---|---|
| Hot | Sweating, vasodilation | Heat lost from body |
| Cold | Shivering, vasoconstriction | Heat conserved/gained |
Key Terms to Remember:
- Thermoregulation: Maintaining body temperature
- Hypothalamus: Brain center controlling temp
- Vasodilation: Vessels widen to lose heat
- Vasoconstriction: Vessels narrow to keep heat
- Shivering: Muscle action generates heat
- Sweating: Evaporation removes heat
Blood Glucose Regulation
What is it?
Blood glucose regulation is how your body keeps glucose (sugar) levels in the blood within a safe range (around 4–7 mmol/L).
The goal is to:
- Prevent hyperglycemia (too much glucose)
- Prevent hypoglycemia (too little glucose)
This is controlled by two hormones from the pancreas:
- Insulin: Lowers blood sugar
- Glucagon: Raises blood sugar
A Negative Feedback Mechanism
Like a thermostat: if glucose is too high or low, your body acts to bring it back to normal.
Scenario 1: After Eating – Blood Sugar Rises
| Step | What Happens |
|---|---|
| 1. Stimulus | Blood glucose level rises (e.g. after sweets) |
| 2. Sensor | Pancreas detects the rise |
| 3. Response | Pancreas releases insulin into blood |
| 4. Effect | Cells absorb glucose, excess stored as glycogen in liver/muscles |
| 5. Outcome | Blood glucose returns to normal |
Negative feedback turns off insulin release.
Scenario 2: Skipping a Meal – Blood Sugar Falls
| Step | What Happens |
|---|---|
| 1. Stimulus | Blood glucose level drops too low |
| 2. Sensor | Pancreas detects the drop |
| 3. Response | Pancreas releases glucagon |
| 4. Effect | Liver breaks down glycogen → glucose released into blood |
| 5. Outcome | Blood glucose rises back to normal |
Negative feedback turns off glucagon release.
Key Terms to Remember:
| Term | Definition |
|---|---|
| Insulin | Hormone that lowers blood sugar |
| Glucagon | Hormone that raises blood sugar |
| Pancreas | Organ that releases both hormones |
| Glycogen | Stored form of glucose |
| Homeostasis | Keeping internal conditions stable |
What If This System Fails?
- Type 1 Diabetes: Pancreas makes no insulin → blood sugar stays high
- Type 2 Diabetes: Cells resist insulin → sugar not absorbed
- Treatment: Insulin injections, balanced diet, exercise
Quick Recap:
| Situation | Hormone Released | Action |
|---|---|---|
| High blood sugar (e.g. after eating) | Insulin | Stores glucose as glycogen |
| Low blood sugar (e.g. fasting, exercise) | Glucagon | Breaks down glycogen into glucose |