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IB Biology HL C3.1 Integration of Body Systems Questions

Practise IB Biology HL C3.1 by tracing reflex pathways and explaining feedback control, endocrine signals, ventilation and plant responses.

Syllabus
First assessment 2025
Course
Biology HL
Level
HL

Exam points

  • Explain emergent system properties as interacting components are organized from cells through tissues and organs.
  • Identify brain-region functions and use lesion, fMRI or movement evidence to explain integrated responses.
  • Trace a rapid withdrawal reflex from sensory input to motor output and skeletal-muscle response.
  • Explain darkness-triggered melatonin secretion and its role in circadian sleep timing.
  • Explain epinephrine effects on heart rate, ventilation and respiratory-fuel availability during stress.
  • Explain hypothalamic-pituitary endocrine control and interpret hormone-response data such as leptin's effect on appetite.
  • Explain medullary feedback control of heart rate and ventilation in response to blood-pressure and CO₂/pH signals.
  • Explain how peristalsis moves food through the intestine from the stomach toward the large intestine.
  • Explain positive shoot phototropism through auxin transport, shaded-side redistribution and acid-growth-driven elongation.
  • Identify auxin and cytokinin as phytohormones and relate their roles to plant growth and gene expression.
  • Explain ethylene-driven fruit ripening as positive feedback affecting nearby fruit.

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 controlC3.1.17 (HL)—Tropic responses in seedlingsC3.1.18 (HL)—Positive phototropismC3.1.19 (HL)—PhytohormonesC3.1.20 (HL)—Auxin efflux carriersC3.1.21 (HL)—Auxin promotes cell growthC3.1.22 (HL)—Auxin and cytokinin interactionsC3.1.23 (HL)—Ethylene and fruit ripening

Question 1

[Maximum number: 1]

A computer model simulation was proposed to assess the removal of extracellular polymeric substances (EPS) from biofilms by using a detachment-promoting agent (DPA).

Simulations on a 60-day-old biofilm after 6 minutes of treatment with DPA and on the same biofilm after 84 minutes of treatment with DPA are shown as a 3D view and a cross section. Dark grey represents bacteria and light grey shows the EPS.

Figure for Question 1 — IB Biology HL

State one reason, other than the formation of an EPS, for the high resistance to antimicrobial agents in biofilm microorganisms.

Question 2

[Maximum number: 1]

Though a single nerve cell does not think, millions of them organized as a brain result in thinking. What kind of property does thinking represent?

A

Anatomical

B

Adaptive

C

Extracellular

D

Emergent

Question 3

[Maximum number: 3]

The diagram shows the liver and its main blood vessels.

Figure for Question 3 — IB Biology HL

Outline the circulation of blood through liver tissue.

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