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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
HL

Exam analysis

Chance of appearing1%of analysed past papers
Latest appearanceMay 2013
Most common paperPaper1
Typical marks1

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

May 2013Paper1 ["HL"] · TZ219[ 1 ]C3.1.3—Integration of organs
Practice this objective

Coverage 2013–2013 · Updated 16 Jul 2026

Organs integrate by sharing materials and control

Organs integrate by sharing materials and control.

An organ system works only when its organs exchange inputs and outputs. Blood can carry oxygen, urea or hormones between organs, while nervous and endocrine signals adjust their activity.

trace source → transport or signal → target → physiological effect.

The liver makes urea, blood carries it to the kidneys, and the kidneys remove it; separating any link breaks the process.

A hormone’s source and target need not be the same organ, and transport is part of the mechanism.

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]


(b) 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.
ConceptIB Biology HL