How DP Biology Is Assessed: Revision Notes

Condensed for quick recall of how the course is assessed. For the full subject overview, use the IB DP Biology subject overview.

Why 80/20 rather than an even split

The 80% external / 20% internal balance reflects that the IA tests focused practical and investigative skill on one self-chosen topic, while the two written papers are needed to sample understanding across the whole syllabus breadth – a single IA, however well executed, cannot demonstrate the same content coverage that two full papers can assess. Keeping this in mind when allocating revision time – proportionally more time on paper-style practice once a solid IA draft exists – reflects where the majority of the final grade actually sits.

The assessment split

Component	Weight	What it involves
Paper 1	36%	Short-answer and data-based questions across the whole syllabus
Paper 2	44%	Short-answer and extended-response questions requiring sustained scientific writing
Internal assessment	20%	An individual scientific investigation, written up in a report of up to 3,000 words

External examination (Papers 1 + 2) = 80%. Internal assessment = 20%. This split is the same at both SL and HL — the papers differ in length and demand, not in this weighting.

Two things not to confuse

• The graded internal assessment is an individually designed, carried out and written investigation.
• The interdisciplinary collaborative sciences project, done with peers from other group 4 subjects, builds investigative skills but is not itself graded — don’t confuse the two when planning your IA timeline.

Why this split matters for revision

Because Paper 2 (44%) outweighs Paper 1 (36%), and Paper 2 specifically requires sustained, extended-response scientific writing (not just short answers), practising structuring a longer written scientific answer is worth dedicated revision time, not just content recall.

The internal assessment in more depth

The IA report is graded against criteria covering the whole investigative process: formulating a focused, testable research question grounded in a clear scientific rationale; designing a method capable of generating sufficient, reliable data to answer it; recording and processing that data appropriately, including a genuine treatment of uncertainty and error; and evaluating the investigation critically, including specific, actionable improvements rather than generic ones. A common weakness examiners note is an evaluation section that lists limitations without connecting them concretely to how they affected the specific data collected – a strong evaluation ties each limitation back to its actual impact on the results, and proposes a feasible, specific improvement rather than a vague one such as “use better equipment.”

Command terms and how each paper uses them

Both papers draw from the same command-term glossary shared across the DP sciences: state, define, identify and describe at the lower end (recall and straightforward description); explain, compare, deduce and suggest in the middle; evaluate, discuss and justify at the top, requiring a reasoned judgement or synthesis across multiple pieces of evidence. Because Paper 2 carries almost half the external mark and specifically requires sustained, extended-response scientific writing, revision time spent deliberately practising evaluate and discuss-style answers – weighing evidence, acknowledging limitations, reaching a justified conclusion – pays off disproportionately there compared with Paper 1’s shorter, more data-focused questions.

How Biology’s assessment compares to its sibling sciences

DP Chemistry and DP Physics share the same overall assessment architecture – two external written papers plus an individually graded internal assessment, alongside the ungraded collaborative sciences project – but each subject organises its papers around its own framework rather than Biology’s broader thematic structure across its topic areas. If you are also studying another Group 4 science, recognising that the shape of assessment (external papers plus IA plus collaborative project) transfers directly, while the specific content organisation does not, avoids wasted time trying to map one subject’s structure onto another’s.

Why extended-response writing deserves dedicated practice

Because Paper 2 specifically requires sustained scientific writing across multiple linked questions, rather than a series of short, disconnected answers, it rewards a different skill from Paper 1’s data-based and short-answer format: structuring a coherent, well-sequenced argument that draws on evidence and terminology across a topic, not just recalling isolated facts. Practising full extended-response answers under timed conditions – not just outlining what would be included – is the most direct way to build this specific skill, since planning an answer and actually writing it fluently under time pressure are genuinely different capabilities.

Self-test

1. What are the three components of DP Biology’s assessment, and their weightings?
2. What’s the word limit on the individually graded scientific investigation?
3. What’s the key difference between the graded IA and the collaborative sciences project?
4. Which paper is weighted more heavily, and what type of writing does it specifically require?
5. Name one common weakness examiners note in a weak IA evaluation section.
6. Why does Paper 2 reward a different skill from Paper 1, beyond simply requiring more content recall?

Answers: 1. Paper 1 (36%), Paper 2 (44%), internal assessment (20%). 2. 3,000 words. 3. The IA is an individual investigation that is formally graded; the collaborative sciences project is done with peers and builds investigative skills but is not itself part of the graded assessment. 4. Paper 2 (44%), which requires extended-response answers demanding sustained scientific writing, not just short answers. 5. Listing limitations without connecting them concretely to their actual impact on the results obtained, or proposing only vague improvements. 6. Because it requires structuring a coherent, well-sequenced argument across linked questions, which is a genuinely different skill from Paper 1’s shorter, more data-focused format — planning and writing fluently under time pressure must both be practised directly.

Official syllabus

International Baccalaureate Organization, Diploma Programme Subject Brief – Sciences: Biology, first assessment 2025, published January 2022 – the same source cited by the full syllabus guide and the subject overview.