IB Biology SL · 2025
Unit 3: Interaction and interdependence
156 past paper questions from 18 papers across 4 exam sessions. See what repeats, then practise the same skills with AI marking.
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SL archive · 2025 to 2026
Unit 3: Interaction and interdependence
Latest exam session: May 2026
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Topics in Unit 3: Interaction and interdependence
In syllabus order. The ring is the share of the marks each one carries.
3.1
Enzymes and metabolism
8% of marks · 12 questions
3.2
Cell respiration
13% of marks · 16 questions
3.3
Photosynthesis
5% of marks · 10 questions
3.5
Neural signalling
15% of marks · 24 questions
3.6
Integration of body systems
8% of marks · 17 questions
3.7
Defence against infectious disease
15% of marks · 23 questions
3.8
Populations and communities
18% of marks · 32 questions
3.9
Transfers of energy and matter
18% of marks · 22 questions
Exam pattern
How often each micro-topic has been examined, year by year. Each label is explained under the grid.
Does it repeat?
Top 4 of 49 micro-topics for the next sitting. Numbers are questions per year.
fewermore
| Micro-topic | 2025 | 2026 |
|---|---|---|
| 6Adaptive immunity, antibodies and memory, 2025: 6 questions | 3Adaptive immunity, antibodies and memory, 2026: 3 questions | |
| 2Competitive exclusion, niche & allelopathy, 2025: 2 questions | 10Competitive exclusion, niche & allelopathy, 2026: 10 questions | |
| 4Variation in the speed of nerve impulses, 2025: 4 questions | 5Variation in the speed of nerve impulses, 2026: 5 questions | |
| 3Differences between anaerobic and aerobic cell respiration in humans, 2025: 3 questions | 4Differences between anaerobic and aerobic cell respiration in humans, 2026: 4 questions |
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Questions on Unit 3: Interaction and interdependence, by exam session
Which papers asked about Unit 3: Interaction and interdependence, and which question numbers. Open a paper to see them highlighted.
May 2026
42 questions across 6 papers
November 2025
25 questions across 4 papers
May 2025
38 questions across 6 papers
Specimen 2025
13 questions across 2 papers
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Frequently asked questions
Short answers about this page.
Which Biology SL exam sessions are covered for Unit 3: Interaction and interdependence?
4 exam sessions from 2025 to 2026, the latest May 2026. Every Paper 1 and 2 in every timezone is read and classified in full, which gives 18 papers in this archive.
Which Unit 3: Interaction and interdependence topic comes up most?
Adaptive immunity, antibodies and memory (3.7.4): in 39% of papers, last seen May 26 P2 TZ3. Usually "Identify", worth about 2.4 marks in a paper that includes it.
Can I see the original question and mark scheme?
No. The wording belongs to the IB. You get the citation, the marks, the command term and the skill tested, plus our own matched practice questions with worked answers and AI marking.
What do "banker", "due" and "rising" mean?
Banker: examined in at least one sitting in four and still appearing. Due: regular before, but absent for the last two exam sessions. Rising: clearly more common in the last two years. Our classification of real papers, not an IB statistic.
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