C3.1.1—System integration
System integration links named stimuli, coordinating structures and effectors so body systems or plant tissues produce an integrated biological response.
- Syllabus
- First assessment 2025
- Objective
- C3.1.1
- Level
- HL
Exam analysis
Chance of appearing1%of analysed past papers
Latest appearanceMay 2014
Most common paperPaper1
Typical marks1
Common command terms
- Identify
- Explain
Scoring notes
- Common mistake
- Naming a brain region without linking it to information integration or coordination.
Recent exam appearances
May 2014Paper1 ["HL"] · TZ12[ 1 ]C3.1.1—System integration
Practice this objective
Coverage 2014–2014 · Updated 16 Jul 2026
Integration joins specialised parts into a working whole
Integration joins specialised parts into a working whole.
In a multicellular organism, tissues, organs and organ systems exchange information and materials so the organism can coordinate one response. Nervous impulses are fast; hormones travel in blood and can act on distant targets.
Name the parts; identify the signal or material crossing between them; then state the coordinated outcome.
During exercise, receptors and the brain increase heart and ventilation activity while blood delivers oxygen to working muscle.
Integration is more than a list of organs: the explanation must include communication and a shared function.
System integration
Assessment in practice
1–3 marksHow it is assessed
This objective is assessed through structured response, commonly using Identify / Explain.
Command terms
Identify / Explain
What earns marks
Mark schemes reward named structures, correct direction of information flow and explanations that keep the sequence causal.
Watch for
Naming a brain region without linking it to information integration or coordination.
Representative question
Question 1
Using the diagram, explain the concept of emergent properties of biofilms.
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
- System integration depends on linking the stimulus to the coordinating structure or signal.
- The pathway for system integration must keep information flow and response direction clear.
- Named tissues, hormones, neurons or effectors give system integration its biological specificity.
- Evidence about system integration is strongest when structure, mechanism and outcome are connected.