IB Biology SL C3.1 Integration of body systems Questions

Practise IB Biology SL C3.1 by tracing reflex arcs, interpreting brain and organ-coordination evidence, and explaining hormonal and feedback control in the body.

81 questions in this syllabus scope, with question parts counted together.

Syllabus
First assessment 2025
Course
Biology SL
Level
SL

Exam analysis

SL · 2010–2025
Papers with this topic64 / 141in the analysed sample
Latest appearanceNovember 2025
Tagged question parts93
Paper types5

Most tested objectives

  1. C3.1.9—Pain reflex arcs13 papers
  2. C3.1.1—System integration11 papers
  3. C3.1.4—Brain as information integration organ11 papers
  4. C3.1.3—Integration of organs9 papers
  5. C3.1.14—Heart rate feedback control9 papers

Common question formats

  • Structured response
  • Definition or recall
  • Diagram interpretation
  • Process explanation
  • Extended response
  • Calculation
  • Experimental design
  • Comparison
  • Data analysis
  • Graph interpretation

Recent exam appearances

November 2025Paper 2 SL · TZ1Q6(c)[ 4 ]
November 2025Paper 1A SL · TZ3Q18[ 1 ]
November 2025Paper 1A SL · TZ1Q16[ 1 ]

141 papers analysed · Tagging incomplete

Exam points

  • Explain how interacting cells, organs, and systems produce coordinated or emergent properties, including hierarchical organisation.
  • Interpret digestive-organ diagrams and blood or duct pathways linking the liver, pancreas, gall bladder, and small intestine.
  • Identify hypothalamus, cerebellum, and medulla roles from brain diagrams, including appetite, coordination, balance, and involuntary control.
  • Interpret fMRI, pupil-reflex, decision-making, or contralateral-vision evidence to explain brain information integration.
  • Trace a pain-withdrawal reflex from receptor through sensory, relay, and motor neurons to a skeletal-muscle effector.
  • Relate melatonin, appetite signals, or pituitary hormones to circadian timing, feeding, or endocrine feedback.
  • Explain heart-rate control by medulla signals, autonomic nerves, adrenaline, and sinoatrial-node activity.
  • Explain CO₂/pH feedback from chemoreceptors through the medulla to ventilation and respiratory muscles.
  • Distinguish enteric control of involuntary peristalsis from CNS control of swallowing or egestion.

Covered syllabus points

C3.1.1—System integrationC3.1.2—Hierarchy in multicellular organismsC3.1.3—Integration of organsC3.1.4—Brain as information integration organC3.1.5—Spinal cordC3.1.6—Input through sensory neuronsC3.1.7—Output through motor neuronsC3.1.8—Nerves as bundlesC3.1.9—Pain reflex arcsC3.1.10—Cerebellum roleC3.1.11—Melatonin and sleepC3.1.12—Epinephrine (adrenaline)C3.1.13—Hypothalamus and pituitary controlC3.1.14—Heart rate feedback controlC3.1.15—Ventilation rate feedback controlC3.1.16—Peristalsis control

Exam points

  • Define an emergent property as a system-level behaviour produced by interactions among components and not predictable from an isolated component.
  • Use biofilm or nervous-system evidence to explain how organization, communication and cooperative interactions create new properties such as EPS architecture, quorum sensing or resistance.

Exam points

  • Explain that multicellular organization forms a hierarchy from cells to tissues, organs, organ systems and whole organisms, enabling properties not present in isolated cells.
  • Use the organized-brain example to identify thinking as an emergent property produced by coordinated interactions among many nerve cells.

Question 1

[Maximum number: 1]

Why do multicellular organisms have emergent properties?

A

They have more genes than unicellular organisms.

B

Properties of unicellular organisms are enhanced by having many cells.

C

All of their genes are expressed whereas unicellular organisms express only some.

D

They show properties that can only result from the interaction of many cells.

Exam points

  • Draw or interpret liver, gall bladder, pancreas and small-intestine duct connections, including the bile and pancreatic ducts joining before the intestine.
  • Explain how blood plasma and hepatic portal transport carry absorbed nutrients and pancreatic hormones between digestive organs and the liver.
  • Relate secretin and pancreatic bicarbonate or dual hepatic blood supply to coordinated digestion and rapid glucose regulation.

Question 1

[Maximum number: 1]

The autonomic nervous system is one part of the peripheral nervous system.

Outline the role of the autonomic nervous system.

Exam points

  • Identify the hypothalamus, cerebellum and medulla/brain stem on brain diagrams and state their scored roles in appetite, coordination, balance and involuntary control.
  • Explain decision-making or contralateral visual processing as integration of excitatory/inhibitory synapses or crossed optic pathways in the cerebral hemispheres.
  • Explain how fMRI, pupil-reflex testing or regional activation evidence reveals brain function and damage.

Question 1

[Maximum number: 1]

Swallowing is a complex coordinated process regulated by the autonomic nervous system.

State the area of the brain that coordinates swallowing.

Exam points

  • Explain how the spinal cord links the brain with peripheral sensory and motor pathways, using lesion evidence that separates sensation from movement.
  • Locate spinal-cord grey-matter synapses and explain how the cord integrates an unconscious reflex response.

Question 1

[Maximum number: 1]

The image shows a castor bean tick (Ixodes ricinus) which is commonly found in woodlands or forest areas. This tick can carry bacteria that cause Lyme disease in humans.

Figure for Question 1 — IB Biology SL

Some symptoms of Lyme disease are caused by damage to the central nervous system (CNS). State both parts of the CNS.
1.
2.

Exam points

  • Identify that sensory neurons carry impulses from receptors to the spinal cord or brain.
  • Explain how sensory receptors detect a stimulus and convert its energy into nerve impulses that can reach the cerebral hemispheres for conscious perception.

Question 1

[Maximum number: 2]

The diagram below shows a reflex arc.

Figure for Question 1 — IB Biology SL

Outline how stimuli can be detected by human sensory receptors.

Exam points

  • State that motor neurons carry impulses from the central nervous system to skeletal-muscle effectors.
  • Explain that voluntary muscle contraction is coordinated through the cerebral hemispheres and motor output to the selected effector.

Question 1

[Maximum number: 1]

The diagram below shows a motor neuron.

Figure for Question 1 — IB Biology SL

State a function of motor neurons.

No public sample questions are available for this syllabus point yet.

Exam points

  • List the sequence of receptor, sensory neuron, relay neuron, motor neuron and skeletal-muscle effector in a pain-withdrawal reflex arc.
  • Explain how sensory, relay and motor neurons transmit a rapid involuntary response through the spinal cord.

Question 1

[Maximum number: 1]

Which of these structures is most likely to be the effector in a pain reflex arc?

A

Grey matter

B

Skeletal muscle

C

Motor neuron

D

Pineal gland

No public sample questions are available for this syllabus point yet.

Exam points

  • Identify the pineal gland as the source of melatonin and explain that darkness or reduced light increases its secretion.
  • Explain or interpret how melatonin modulates circadian sleep timing, including jet-lag or screen-light effects.

Question 1

[Maximum number: 1]

Which hormone regulates the hours of sleep and wakefulness?

A

Thyroxine

B

Insulin

C

Leptin

D

Melatonin

Exam points

  • Identify adrenal epinephrine secretion during stress or intense activity and explain its increase of sinoatrial-node activity and heart rate.
  • Explain how epinephrine increases ventilation, blood flow and respiratory-substrate availability to prepare skeletal muscles for action.

Question 1

[Maximum number: 1]

What will always cause an increase in heart rate?

A

Nerve impulses from the medulla

B

Signals from the sinoatrial node

C

Secretion of epinephrine (adrenaline)

D

High levels of leptin

Exam points

  • Explain how hypothalamic hormone signals regulate appetite and homeostasis, using leptin or ghrelin evidence.
  • Identify pituitary hormones such as FSH and explain their regulation of gonadal function through feedback.

Question 1

[Maximum number: 1]

Antiretroviral drugs are used to treat Human Immunodeficiency Virus (HIV) infections. Zidovudine (ZDV) and nevirapine (NVP) are examples of antiretroviral drugs. There are concerns that these drugs may be toxic to body cells in mitosis. In a study using Allium cepa, root tips were exposed to the drugs for 96 hours at a range of concentrations. The control treatment was a drug concentration of 0μ mol0 \mu \mathrm{~mol}. In the graph, root lengths after the 96-hour treatment period are expressed as a percentage of the length of the control.

Figure for Question 1 — IB Biology SL

Outline the role of leptin in appetite control.

Exam points

  • Explain how medulla nerve impulses, the sinoatrial node and myogenic heart tissue adjust heart rate during exercise or changing demand.
  • Identify the roles of nerves, hormones and pacemaker activity in feedback control of heart rate.

Question 1

[Maximum number: 4]

Explain how signals from the sinoatrial node (SAN) pass to other parts of the heart, so that the beating of the heart is coordinated.

Exam points

  • Explain how CO₂-driven blood-pH changes are detected and alter ventilation through the medulla and respiratory muscles.
  • Interpret arterial-pH or atmospheric-CO₂ data to relate chemoreceptor feedback to ventilation rate and air volume.

Question 1

[Maximum number: 1]

The graph shows the effect of atmospheric carbon dioxide (CO2) concentration (measured as partial pressure) on the ventilation rate (measured as total volume of air breathed in and out from the lungs in one minute) of a mammal.

Figure for Question 1 — IB Biology SL

Atmospheric CO2\mathrm{CO}_{2} partial pressure / kPa

Which of the following explains the results obtained at high atmospheric CO2\mathrm{CO}_{2} concentration?

A

The brainstem stimulates increased contraction of the diaphragm and intercostal muscles when chemoreceptors detect a drop in blood pH .

B

Stretch receptors in the brainstem send impulses to the lungs to increase ventilation rate.

C

Baroreceptors sense a build-up of CO2\mathrm{CO}_{2} and send signals to the diaphragm and intercostal muscles.

D

The pituitary gland stimulates the brainstem when blood plasma becomes more acidic.

Exam points

  • Explain that enteric nervous system signals coordinate involuntary peristaltic waves in gut smooth muscle to move material along the intestine.
  • Distinguish CNS control of voluntary swallowing or egestion from enteric control of involuntary peristalsis.

Question 1

[Maximum number: 1]

What describes the control mechanisms for peristalsis that ensure coordinated passage of material through the digestive system?

A

Voluntary control by the central nervous system

B

Involuntary control by the enteric nervous system

C

Involuntary control by the central nervous system

D

Voluntary control by the enteric nervous system

Question 1

[Maximum number: 2]

The autonomic nervous system is one part of the peripheral nervous system.

Question (a)

(a)

Outline the role of the autonomic nervous system.

[ 1 ]

Question (b)

(b)

Identify the control centre for the autonomic nervous system.

[ 1 ]

Question 2

[Maximum number: 4]

Swallowing is a complex coordinated process regulated by the autonomic nervous system.

Question (a)

(a)

Describe the autonomic nervous system.

[ 2 ]

Question (b)

(b)

State the area of the brain that coordinates swallowing.

[ 1 ]

Question (c)

(c)

Receptors in the mouth send information to the brain about the food being chewed. Outline one type of sensory receptor found in the mouth that provides information to the brain when hot food is eaten.

[ 1 ]
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