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C3.1.3—Integration of organs

Integration of organs links named stimuli, coordinating structures and effectors so body systems or plant tissues produce an integrated biological response.

Syllabus
First assessment 2025
Objective
C3.1.3
Level
SL

Exam analysis

Chance of appearing4%of analysed past papers
Latest appearanceNovember 2024
Most common paperPaper3
Typical marks1–2

Common command terms

  • Identify
  • Explain
  • Draw
  • Deduce
  • Suggest
  • Outline
  • Describe

Scoring notes

Common mistake
Giving a general body-system answer without the specific pathway step for integration of organs.

Recent exam appearances

November 2024Paper3 ["SL"] · TZ16(a)[ 2 ]C3.1.3—Integration of organs
May 2024Paper3 ["SL"] · TZ16(a)[ 1 ]C3.1.3—Integration of organs
May 2017Paper3 ["SL"] · TZ119[ 2 ]C3.1.3—Integration of organs
May 2017Paper3 ["SL"] · TZ118(b)[ 3 ]C3.1.3—Integration of organs
November 2015Paper2 ["SL"] · TZ04(a)[ 2 ]C3.1.3—Integration of organs
Practice this objective

Coverage 2013–2024 · Updated 16 Jul 2026

Organs integrate by sharing materials and control

Animal organs are integrated by nervous and hormonal messages and by blood transport of materials and energy between organs.

Integration route Message or material Typical pattern
Nervous signalling Electrical impulses and neurotransmitters Rapid, targeted, usually short-lived
Endocrine signalling Hormones carried in blood Slower, distributed to distant receptor-bearing cells, often longer-lived
Blood transport Oxygen, nutrients, heat and wastes Connects organ inputs and outputs continuously

During exercise, motor nerves stimulate skeletal muscles, epinephrine coordinates responses in several organs, and blood carries oxygen and glucose to muscle while transporting carbon dioxide away.

Blood is both a transport route for hormones and a carrier of non-message materials. Integration requires source, route, target and coordinated outcome—not just a list of organs.

Integration of organs

Assessment in practice

1–2 marks
How it is assessed

This objective is assessed through structured response, commonly using Identify / Explain / Draw.

Command terms

Identify / Explain / Draw / Deduce / Suggest / Outline / Describe

What earns marks

Mark schemes reward named structures, correct direction of information flow and explanations that keep the sequence causal.

Watch for

Giving a general body-system answer without the specific pathway step for integration of organs.

Representative question

Question 1

[Maximum number: 3]

Pancreatic secretions contain sodium hydrogen carbonate, making them basic.
Deduce the significance of the response by the pancreas to secretin.

Body-System Integration

  • Nervous signals, hormones and blood transport integrate organs into coordinated systems; emergent functions arise from their interactions.
  • Sensory neurons carry receptor input to the CNS; motor neurons carry output to effectors. Mixed nerves contain both fibre types.
  • Reflex arcs provide rapid involuntary responses through sensory, relay and motor neurons. The spinal cord also links the brain and peripheral nerves.
  • Cerebral hemispheres support conscious processing; the cerebellum coordinates movement and balance; the medulla adjusts ventilation and heart activity.
  • The hypothalamus links nervous and endocrine control through the pituitary. Pineal melatonin helps time sleep; adrenal epinephrine supports acute stress responses.
  • Baroreceptors and chemoreceptors provide feedback about pressure, CO2, pH and O2.
  • The CNS controls voluntary swallowing and egestion, while the enteric nervous system coordinates gut peristalsis.

Concept essentials

  • Integration of organs depends on linking the stimulus to the coordinating structure or signal.
  • The pathway for integration of organs must keep information flow and response direction clear.
  • Named tissues, hormones, neurons or effectors give integration of organs its biological specificity.
  • Evidence about integration of organs is strongest when structure, mechanism and outcome are connected.