Safety and evidence boundary
This week uses fictional organisms, classroom-safe models, and non-diagnostic datasets. Do not collect personal medical information, change medication, perform extreme-temperature exposure, deliberately alter blood glucose, restrict food or water, or use physiological measurements to diagnose health conditions.
Explicit science instruction
Positive feedback amplifies an initial change rather than opposing it. It is useful when a process must move rapidly toward completion, but it requires a stopping condition, depletion of a component, an external event, or another regulatory process to prevent indefinite amplification.
Examples often taught include blood-clotting cascades and contraction signaling during labor, but this course treats them only as conceptual examples—not as personal medical guidance. Feedforward differs from feedback because it acts in anticipation of a predicted disturbance before the regulated variable has fully changed.
Vocabulary: positive feedback; amplification; termination condition; threshold; feedforward; anticipatory response; gain; runaway process.
Worked example with reasoning
In a fictional wound-sealing model, activated cell fragments release a signal that recruits and activates more fragments. Activation therefore increases further activation. The loop is positive feedback. It ends when the damaged surface is sealed and the activating conditions decline. Without a termination condition, the model is incomplete.
Guided question
Why is “positive feedback increases the response” not enough to explain a stable biological system?
Independent work
- Create one negative-feedback and one positive-feedback diagram.
- For the positive loop, state the termination condition.
- Write one example of feedforward control in a fictional organism.
- Explain how feedforward differs from negative feedback.
Misconception check
Positive feedback is not automatically harmful, and negative feedback is not automatically beneficial. The labels describe whether a response amplifies or opposes a change.
Formative understanding check
A response begins before the regulated variable measurably changes because a predictive cue is detected. Is that feedback?
Show the worked response
Not necessarily. If the response is triggered by an anticipated disturbance before the regulated variable changes, it is better described as feedforward or anticipatory control.
Open-book formative practice only; not an official mastery attempt or grade.
Mentor evidence conference
Ask Archaemenes to test whether your feedback model identifies the variable, sensor, integrating logic, effector, direction of response, and limitation without giving protected assessment answers.
Open Archaemenes for this lessonTeacher guidance
Foundation: compare two pre-labeled loop diagrams. Core: justify loop type from direction of response and identify the stopping condition. Extended: analyze systems combining feedforward with negative feedback and discuss why layered control can improve stability.
Preserve learning evidence
Keep the model, calculation or graph, correction note, and evidence-based explanation in the matching Week 14 evidence field.
Return to tuesday Evidence Workspace