Q BankQuestion BankDocsDocuments

D3.3.2—Negative feedback loops

Negative feedback returns a changed variable toward its set point, while positive feedback amplifies a change for a short time.

Syllabus
First assessment 2025
Objective
D3.3.2
Level
HL

Negative Regulation Reverses a Deviation

Negative regulation reduces the original change so a regulated variable returns toward its normal range.

The response opposes the disturbance: a rise triggers actions that lower it, and a fall triggers actions that raise it. This stabilizes rather than amplifies the system.

Ask whether the response moves the variable in the opposite direction to the initial deviation.; identify the signal, controller and effector

If body temperature rises, sweating and vasodilation increase heat loss, reducing the rise. This gives a concrete prediction from the stated condition.

Negative means opposing the deviation, not harmful or always below the set point. Interpret the result within the stated biological model and limits.

Negative feedback loops

Assessment in practice

4 marks
How it is assessed

This objective is assessed through essay response, commonly using Discuss.

Command terms

Discuss

What earns marks

Build the answer around this relationship: Negative feedback opposes the original change.

Representative question

Question 1

[Maximum number: 4]

Discuss the use of positive and negative feedback to control levels of variables.

Retrieve the Core Homeostasis Route

Core D3.3 is secure when every example becomes a feedback route: identify the variable, detect deviation, coordinate a response, activate effectors, and reverse the change. Glucose and temperature are the key worked examples.

  • stable internal environment within narrow limits
  • detects deviation from set point and reverses it
  • insulin lowers high glucose; glucagon raises low glucose
  • hypothalamus coordinates cooling or warming responses

Core Homeostasis

Core homeostasis answers should use a control-loop structure, not a list of responses. The response starts with the variable and set point, then explains how the body detects deviation and activates the response that reverses it. Apply that loop to glucose, diabetes, or temperature.

  • Define homeostasis as maintaining stable internal conditions within narrow limits.
  • Use negative feedback language: receptor, coordinator, effector, set point, and reverse the deviation.
  • Apply the loop to insulin/glucagon, diabetes types, or hot/cold thermoregulation responses.

Concept essentials

  • Negative feedback opposes the original change.
  • Positive feedback amplifies a change instead of restoring equilibrium.
  • Homeostasis mainly depends on negative feedback loops.
ConceptIB Biology HL