Complete Guide to IB Biology

What Is IB Biology?

IB Biology is a Group 4 science subject in the IB Diploma Programme. It delves into living organisms, their interactions, and the biological processes that underpin life. The 2025 syllabus is structured around four core themes, explored across four levels of biological organization (molecules, cells, organisms, ecosystems), and emphasizes scientific inquiry and real-world connections.

Curriculum Structure (2025 Syllabus)

The course is defined by four major themes, each present in both Standard Level (SL) and Higher Level (HL):

• Theme A – Unity and Diversity:
  Understanding how shared biochemical foundations support life’s variety and evolution.
• Theme B – Form and Function:
  Exploring how organism structures reflect their roles and survival.
• Theme C – Interaction and Interdependence:
  Examining systems through the lens of interactions and emergent properties.
• Theme D – Continuity and Change:
  Investigating mechanisms that maintain life balance and drive evolution.

These themes provide a conceptual framework that connects different aspects of biology across scales and contexts

Core Topics

All students at SL and HL study these essential topics:

• Cell Biology – cell structure, transport systems, origins of cells, viruses
• Molecular Biology – biomolecules, metabolism, DNA/RNA, photosynthesis, respiration
• Genetics – inheritance patterns, meiosis, genetic modification
• Ecology – ecosystem dynamics, energy flow, biodiversity
• Evolution and Biodiversity – mechanisms of evolution, classification

HL students cover these in greater depth and additionally study subjects like muscle physiology, chemical signaling, gene expression, and cladistics.

HL-Only Topics

Higher Level students have access to advanced content such as:

• Muscle and motility
• Chemical and neural signaling
• Gene expression mechanisms
• Virus structure and classification
• Classification and cladistic relationships

Practical Work & Investigations

• SL students complete roughly 40 hours of practical work.
• HL students complete 60 hours, reflecting a higher level of complexity and depth.
• Practical tasks include experimental investigations, collaborative science projects, labs, and data analysis

Teaching Hours

• SL: approximately 150 hours
• HL: approximately 240 hours, including additional practical hours

Assessment Structure

IB Biology assessment includes:

• External Examinations (80% of total grade):
  • Paper 1 – multiple-choice and data questions (~1.5–2 hours)
  • Paper 2 – short and extended-response questions (~1.5–2.5 hours)
• Internal Assessment (IA) – practical investigation (~20% of grade; 10 hours work for SL and HL)

Note: The 2025 Biology syllabus has removed Option-based content and Paper 3.

Scientific Inquiry & Skills

Students gain hands-on experience and develop essential scientific abilities, including:

• Experimental techniques (e.g., microscopy, assays)
• Data analysis, including statistical tests
• Critical thinking and evaluation
• Use of technology (software, sensors)
• Ethical reasoning and scientific rigor

Why Students Choose SL or HL

• SL provides solid foundational knowledge and practical skills within a manageable timeframe.
• HL offers deeper theoretical exploration and more advanced practical work, suited for biotech, medicine, environmental science, or research-oriented careers.

Career Relevance

Graduates of IB Biology often pursue higher education or careers in fields such as:

• Medicine, Veterinary Science, Nursing
• Biotechnology and Biochemistry
• Environmental Science and Ecology
• Genetics, Neuroscience, Public Health

Tips to Succeed in IB Biology

• Learn and apply IB command terms (e.g., define, compare, evaluate)
• Connect concepts across themes—e.g., how molecular biology links to ecology through metabolism
• Build strong data interpretation skills
• Plan and execute your IA topic early—focus on clear research questions, valid methods, and critique
• Use diagrams, models, and visual aids for complex processes
• Regularly practice with past exam papers to familiarize yourself with question styles

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Need support? RevisionDojo offers comprehensive tools tailored to the IB Biology 2025 syllabus:

• Topic summaries aligned with the four themes
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Final Thoughts

The 2025 IB Biology syllabus introduces a clear, concept-driven structure with strong emphasis on interconnected themes, practical investigations, and scientific inquiry. Whether at SL or HL, students develop vital analytical skills, practical know-how, and insight into living systems—excellent preparation for science-driven pathways in higher education and beyond.