IB Biology HL · 2025
Unit 3: Interaction and interdependence
86 past paper questions from 8 papers across 2 exam sessions. See what repeats, then practise the same skills with AI marking.
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HL archive · 2025 to 2026
Unit 3: Interaction and interdependence
Latest exam session: May 2026
- questions
- 86
- questions
- papers
- 8
- papers
- exam sessions
- 2
- exam sessions
- micro-topics
- 41
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 marks12 of the 145 marks across the 8 Biology HL papers analysed (8%) were on this topic. A past-paper pattern, not a guarantee for your next paper. · 10 questions
3.2
Cell respiration
12% of marks17 of the 145 marks across the 8 Biology HL papers analysed (12%) were on this topic. A past-paper pattern, not a guarantee for your next paper. · 8 questions
3.3
Photosynthesis
13% of marks19 of the 145 marks across the 8 Biology HL papers analysed (13%) were on this topic. A past-paper pattern, not a guarantee for your next paper. · 10 questions
3.4
Chemical signalling
13% of marks19 of the 145 marks across the 8 Biology HL papers analysed (13%) were on this topic. A past-paper pattern, not a guarantee for your next paper. · 12 questions
3.5
Neural signalling
12% of marks18 of the 145 marks across the 8 Biology HL papers analysed (12%) were on this topic. A past-paper pattern, not a guarantee for your next paper. · 10 questions
3.6
Integration of body systems
1% of marks1 of the 145 marks across the 8 Biology HL papers analysed (1%) were on this topic. A past-paper pattern, not a guarantee for your next paper. · 1 question
3.7
Defence against infectious disease
14% of marks21 of the 145 marks across the 8 Biology HL papers analysed (14%) were on this topic. A past-paper pattern, not a guarantee for your next paper. · 12 questions
3.8
Populations and communities
16% of marks23 of the 145 marks across the 8 Biology HL papers analysed (16%) were on this topic. A past-paper pattern, not a guarantee for your next paper. · 14 questions
3.9
Transfers of energy and matter
10% of marks15 of the 145 marks across the 8 Biology HL papers analysed (10%) were on this topic. A past-paper pattern, not a guarantee for your next paper. · 9 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 41 micro-topics for the next sitting. Numbers are questions per year.
fewermore
| Micro-topic | 2025 | 2026 |
|---|---|---|
| 2Types of signalling and hormones (steroid vs peptide), 2025: 2 questions | 5Types of signalling and hormones (steroid vs peptide), 2026: 5 questions | |
| 5Interspecific relationships, 2025: 5 questions | 1Interspecific relationships, 2026: 1 question | |
| 3Competitive exclusion, niche & allelopathy, 2025: 3 questions | 1Competitive exclusion, niche & allelopathy, 2026: 1 question | |
| 3Antibiotics, resistance and zoonoses, 2025: 3 questions | 1Antibiotics, resistance and zoonoses, 2026: 1 question |
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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
15 questions across 2 papers
May 2025
50 questions across 6 papers
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Frequently asked questions
Short answers about this page.
Which Biology HL exam sessions are covered for Unit 3: Interaction and interdependence?
2 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 8 papers in this archive.
Which Unit 3: Interaction and interdependence topic comes up most?
Types of signalling and hormones (steroid vs peptide) (3.4.2): in 50% of papers, last seen May 26 P2 TZA. Usually "identify", worth about 3 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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