Year 9 Science · AC9S9U01

Body systems, homeostasis and negative feedback

Learn how receptors detect change, nervous and endocrine pathways coordinate responses, effectors act, and negative feedback helps keep internal conditions within a…

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Key conceptTeach from the board

Coordination is a system, not one organ acting alone

A stimulus is a detectable change. A receptor detects it. A coordinating centre processes information, and an effector such as a muscle or gland produces the response. The nervous system sends fast electrical impulses along neurons; the endocrine system releases hormones that travel in blood and usually act more slowly but for longer.

Negative feedback

Many internal variables fluctuate around a normal range. If a variable moves too far from that range, a corrective response opposes the change. As the variable returns toward range, the corrective signal reduces. This is negative feedback.

Worked examplesWe do

Worked examples

AC9S9U01 - Body systems, homeostasis and negative feedback
Example 1

A student steps into cold air. Identify a likely stimulus and one receptor.

Example 2

Choose whether a rapid withdrawal reflex is mainly nervous or endocrine and justify the choice.

Example 3

Complete: stimulus → receptor → ______ → effector → response.

Example 4

Explain why reduced sweating as body temperature falls back toward range is consistent with negative feedback.

Curriculum examplesCopied content

Australian Curriculum v9.0 — AC9S9U01: compare the role of body systems in regulating and coordinating responses to stimuli and describe negative feedback.

Victorian Curriculum F–10 Version 2.0 — Levels 9–10, VC2S10U02:Exact direct content relationship for nervous/endocrine regulation and homeostasis.

NSW Science 7–10 Syllabus (2023) — Stage relationship:Supporting the closest explicit living-systems foundation is Stage 4 SC4-LIV-01; Stage 5 Working Scientifically can assess the evidence and modelling skills. SkillrHub does not invent a Stage 5 homeostasis outcome.

Lesson componentAC v9VictoriaNSW
Control-system teaching + examplesDirect AC9S9U01Direct VC2S10U02Supporting living-systems knowledge
Reasoning and transferApplies feedback modelBand-level applicationStage 5 Working Scientifically support
AssessmentDescriptor-level explanationLevels 9–10 depthNo false one-to-one equivalence
Questions and answersWith answers
  1. Why is negative feedback important? It limits deviations from suitable internal ranges by opposing change.
  2. How do nervous and endocrine systems differ? Nervous signals travel rapidly along neurons; endocrine signals are hormones carried in blood and are usually slower and longer lasting.
  3. What makes an explanation complete? It links stimulus, detection, coordination, effector action and how the response changes the original variable.
  4. Does homeostasis mean “no change”? No. It means regulation within limits despite ongoing disturbances.
Practice and reviewReady for practice
  • “Negative” means harmful. Correction: negative feedback means the response opposes the original change.
  • Homeostasis keeps values perfectly constant. Correction: values vary within suitable ranges.
  • Nerves and hormones do the same job in the same way. Correction: compare electrical neural signalling with chemical hormonal signalling.
  • One organ system works independently. Correction: regulation depends on interacting receptors, coordinators, effectors and transport systems.
Curriculum alignmentStart here
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