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E2.2 · Build a model of the homeostatic feedback process
Learn to build a model of the homeostatic feedback process through clear examples and targeted practice.
Ontario Grade 12 Biology
Homeostasis
Follow a change from sensor to response
Homeostasis is the regulation of internal conditions within a workable range. A feedback model can help explain how an organism detects a change and responds. For a familiar example, consider body temperature rising above its usual range. The important parts are a variable, a sensor, a control centre, an effector, and a response that changes the variable.
What you will learn
- Label every component of a feedback loop.
- Explain why a negative-feedback response opposes the original change.
- Describe the limits of a simplified model.
Start with a measurable variable
Choose a variable such as core body temperature, not a vague label such as “the body is upset.” State the direction of the disturbance: temperature rises above the usual range. Receptors detect the change and communicate information to a control centre. The centre coordinates an appropriate response through effectors.
A flow chart may read: rising temperature → temperature receptors → control centre → sweat glands and skin blood vessels → greater heat loss. The arrows represent information or physiological effects; they do not mean that heat physically travels from a receptor to the brain.
Close the loop
As sweating and increased skin blood flow support heat loss, temperature can move back toward its usual range. This response opposes the original rise, so it is called negative feedback. “Negative” does not mean harmful. If temperature falls below the range, a different response can reduce heat loss or increase heat production.
A feedback loop is not a promise of perfect control. Illness, dehydration, intense heat, or other conditions can overwhelm a response. It is more accurate to say that the system tends to regulate within a range than to claim that it fixes temperature at one exact number.
Evaluate the model
The five-box flow chart deliberately simplifies many nerves, hormones, organs, and time delays. It is useful when each box has a specific job and the direction of the response can be checked. It cannot, by itself, tell us the exact rate of sweating or predict a clinical outcome. Those claims would need measurements and a more detailed model.
To test a proposed diagram, ask: Is the variable named? Does the sensor detect that variable? Does the effector actually change it? Does the response reduce or amplify the original disturbance? Label the loop negative feedback only if it reduces the disturbance.
Worked example
Correct a temperature loop
A diagram says: temperature rises → receptors detect it → control centre → sweating → temperature rises further. What must change?
- Track the disturbanceThe original change is a rise in temperature.
- Check the effectorSweating allows evaporation and supports heat loss.
- Close the loopThe final arrow should point toward temperature returning to its usual range, not rising further.
Answer: Rising temperature → detection → coordinated sweating → increased heat loss → temperature moves back toward its usual range.
Check: The response opposes the starting change, so the example is negative feedback.
Common mistakes and how to avoid them
Calling negative feedback a harmful or decreasing response in every case.
Correction: It means the response opposes the initial change; the effector may increase or decrease its activity.
Lesson summary
- A feedback model names a variable, sensor, control centre, effector, and response.
- Negative feedback tends to oppose a disturbance.
- A simple flow chart clarifies direction but cannot replace measurements or medical assessment.
Check your understanding
Question 1
What makes a temperature response negative feedback?
- It always makes temperature decrease
- It opposes the initial change and tends to restore a workable range
- It has no control centre
Show answer and explanation
It opposes the initial change and tends to restore a workable range
The response is defined by opposing the disturbance, whether the original change was upward or downward.
Key terms
- Effector
- A tissue or organ that carries out the coordinated response.
- Negative feedback
- A response loop that tends to reduce its initiating disturbance.
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Published by DoAssignment. This reviewed lesson follows Ontario Grade 12 Biology (SBI4U), expectation E2.2. It is a study resource, not an official curriculum publication.
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