IB Science Subjects: How to Choose Between Physics, Chemistry, and Biology
Choosing between IB science subjects shapes more than just your timetable for the next two years. It directly influences your IB score, your workload, and (most critically) whether you meet the prerequisites for the university degree you're working towards. Pick the wrong subject, and you might spend two years grinding through content that doesn't suit you, only to find the door to your preferred course is closed anyway.
Here’s how to make the right choice.
Quick Answer
Biology is content-heavy and memorisation-driven, with minimal maths. It’s ideal for students drawn to living systems and aspiring healthcare professionals.
Chemistry is the "bridge" science, where problem-solving meets biological concepts, and it's the most commonly required subject for medicine and pharmacy in Australia.
Physics is the most maths-intensive and abstract of the three IB science subjects.
Always check Australian university prerequisites before locking in your choices.
HL vs SL matters enormously: the gap in content and exam demand is significant for all three subjects.
What Makes Each IB Science Subject Different?
IB Biology: Memorisation-Heavy, Concept-Rich
Biology is the biggest content load of the three IB science subjects. HL Biology students cover significantly more content than SL, including advanced topics such as gene expression, viruses, and genome sequencing. Expect a lot of diagrams, processes, and terminology to internalise.
Biology rewards students who enjoy reading, understanding systems, and connecting big ideas. It doesn't require strong maths skills, which makes it accessible to a wider range of learners. That said, don't underestimate it at HL. HL exams are longer and more demanding, typically lasting around 3 hours compared to 2 hours for SL.
Best for: Students interested in medicine, nursing, ecology, biomedical science, or any life sciences pathway.
IB Chemistry: The Bridge Between Biology and Physics
Chemistry sits in the middle of the biology vs chemistry vs physics debate. It blends conceptual understanding with problem-solving, lab work, and a level of mathematical application that sits between Biology and Physics. Chemistry HL involves a heavy workload, requiring both theoretical understanding and practical lab work.
What sets Chemistry apart is its relevance. Chemistry underpins much of modern medicine, from drug design to metabolism and diagnostics, chemical principles are deeply embedded in medical education. For that reason, it's the most strategically valuable IB science subject for a wide range of university pathways.
Best for: Students targeting medicine, pharmacy, dentistry, chemical engineering, or biochemistry.
IB Physics: Maths-Driven, Abstract, and Rewarding
Physics is the most mathematically intensive of the three IB science subjects. It covers mechanics, thermal physics, waves, electricity, and more, with a focus on abstract reasoning and quantitative problem-solving. The abstract concepts and mathematical rigour of Physics HL can be daunting, requiring a strong conceptual foundation and the ability to apply mathematical models to physical scenarios.
Physics has the smallest content volume of the three sciences. If you love maths and logical thinking more than memorisation, Physics can play to your strengths. IB Physics primarily utilises algebra and trigonometry rather than calculus, so a solid foundation in secondary maths goes a long way.
Best for: Students aiming for engineering, computer science, architecture, or physics-based degrees.
Australian University Prerequisites: Check Before You Choose
This is where the biology vs chemistry vs physics decision gets serious. Choosing a subject you enjoy is important, but choosing one that closes off your preferred degree can be a costly mistake.
Engineering typically requires Maths AA HL and Physics HL. Medicine usually requires Chemistry HL and Biology HL. For Australian medical schools, students need to take chemistry and a mid-level maths at a minimum.
Medicine/dentistry/pharmacy: Chemistry HL is non-negotiable at most Australian universities. Biology HL is strongly preferred alongside it.
Engineering: Physics HL and Maths AA HL are the standard expectation.
Science, biomedical, or research degrees: Check each university directly – prerequisites vary by institution and program.
Every Australian university publishes its IB-specific prerequisites. Before you finalise your IB science subjects, spend 20 minutes on the admissions pages of your top two or three target universities. If you are planning on applying to overseas universities, you will also need to check their specific prerequisites.
HL vs SL: Which Level Should Your Child Choose?
HL Biology, Chemistry, and Physics include detailed theory and extended experiments, requiring more practice and additional practical assessments compared to SL. HL students have 240 recommended hours of instruction, compared to 150 for SL students.
The general rule: take a science at HL if it's required for your target degree and you're strong in it. Taking Physics HL just because it "looks impressive" while struggling with maths concepts is a recipe for a disappointing score. A strong Chemistry SL beats a weak Physics HL every time.
A Note on Maths Pairing
If you’re doing two or more IB science subjects, your maths choice matters too. Maths AA is geared towards students with a strong proficiency in maths who enjoy exploring more challenging mathematical concepts. It’s ideal for those planning to pursue careers that heavily rely on mathematical principles, such as Physics or Computer Science.
Maths AI suits students taking Biology or a humanities-heavy combination. It's worth aligning the maths course to the science pathway early, since both decisions affect workload and university eligibility. You can find a fuller breakdown of the IB diploma requirements in our separate guide.
The Biggest Mistake Students Make
Picking the science that seems easiest. Every year, students choose Biology at HL because they think it'll be a lighter load, but then get surprised by the sheer volume of content. Others avoid Chemistry because of the lab work, only to discover two years later that it was the one prerequisite standing between them and their medical application.
Choose based on:
Genuine strengths, not what sounds manageable
University prerequisites (check them early)
Career direction. Even a rough idea is better than none
Get the Right Guidance from the Start
The IB science subject decision is worth taking seriously, but you don't have to figure it out alone. Little Geniuses’ IB online tutors work one-on-one with students across all three sciences, helping them not only choose the right subjects but build the skills and confidence to excel in them. Whether your child is just starting the IB or already a couple of terms in, our online tutors across Australia tailor every session to exactly where they are and where they're heading.
Explore how our online tutoring in Australia supports IB students and gives your child the advantage they deserve.