C3.1.18 (HL)—Positive phototropism
Positive phototropism links named stimuli, coordinating structures and effectors so body systems or plant tissues produce an integrated biological response.
- Syllabus
- First assessment 2025
- Objective
- C3.1.18
- Level
- HL
Exam analysis
Chance of appearing5%of analysed past papers
Latest appearanceNovember 2024
Most common paperPaper1
Typical marks1–4
Common command terms
- Identify
- Outline
- Explain
- Describe
Scoring notes
- Common mistake
- Treating low oxygen as the only trigger and omitting carbon-dioxide-driven pH change.
Recent exam appearances
November 2024Paper2 ["HL"] · TZ08(a)[ 4 ]C3.1.18 (HL)—Positive phototropism
May 2022Paper1 ["HL"] · TZ233[ 1 ]C3.1.18 (HL)—Positive phototropism
May 2021Paper2 ["HL"] · TZ16(b)[ 5 ]C3.1.18 (HL)—Positive phototropism
May 2018Paper1 ["HL"] · TZ230[ 1 ]C3.1.18 (HL)—Positive phototropism
May 2017Paper1 ["HL"] · TZ134[ 1 ]C3.1.18 (HL)—Positive phototropism
Practice this objective
Coverage 2014–2024 · Updated 16 Jul 2026
Concept essentials
- Positive phototropism depends on linking the stimulus to the coordinating structure or signal.
- The pathway for positive phototropism must keep information flow and response direction clear.
- Named tissues, hormones, neurons or effectors give positive phototropism its biological specificity.
- Evidence about positive phototropism is strongest when structure, mechanism and outcome are connected.