IB DP Biology D3.3 Homeostasis Study Notes - New Syllabus -2025
IB DP Biology D3.3 Homeostasis Study Notes – New syllbaus
IB DP Biology D3.3 Homeostasis Study Notes at IITian Academy focus on specific topic and type of questions asked in actual exam. Study Notes focus on IB Biology syllabus with guiding questions of
- How are constant internal conditions maintained in humans?
- What are the benefits to organisms of maintaining constant internal conditions?
Standard level and higher level: 2 hours
Additional higher level: 2 hours
D3.3.1—Homeostasis as maintenance of the internal environment of an organism
- Homeostasis refers to the regulation of the internal environment in multicellular organisms to maintain optimal conditions.
- In plant cells, the environment includes the cell wall and its fluid.
- In animal cells, the extracellular matrix (collagen, elastin, etc.) and tissue fluid fill spaces between cells.
- Blood (plasma) acts as tissue fluid, fully separating cells.
Importance of Homeostasis
- Maintains stable conditions inside the body despite external changes.
- Regulated variables include:
- Blood glucose concentration
- Blood osmotic concentration
- Blood pH
- Core body temperature
- Ensures optimal functioning of cells and organs.
D3.3.2—Negative feedback loops in homeostasis
Feedback control helps regulate internal conditions by adjusting physiological processes based on outcomes.
Types of Feedback Control
Negative Feedback
- Restores the original level when a variable moves above or below the set point.
- Maintains stability and helps in homeostasis.
- Example: Regulation of body temperature, blood sugar levels, and osmotic balance.
Positive Feedback
- Increases the gap between the original level and the new level.
- Leads to an amplified response instead of restoring balance.
- Example: Childbirth contractions (oxytocin release) and blood clotting.
- Not commonly used in homeostasis because it promotes change rather than stability.
Importance of Negative Feedback
- Essential for maintaining a stable internal environment.
- Requires energy but allows organisms to survive in extreme environments.