IB Diploma Programme Biology: Subject Overview

As one of the three natural sciences in the IB Diploma Programme, Biology is primarily concerned with the study of life and living systems. Biologists make sense of the world through a variety of approaches and techniques, controlled experimentation and collaboration. Through the study of DP Biology, students explore interactions at different levels of biological organization, from molecules and cells to ecosystems and the biosphere.

Scientific inquiry

Integral to the DP Biology experience is learning through scientific inquiry. With an emphasis on experimental work, students ask questions, design experiments, collect and analyse data, collaborate with peers, and reflect, evaluate and communicate their findings.

Aims

Through the overarching theme of the nature of science, the course aims to enable students to:

1. develop conceptual understanding connecting different areas of the subject, and other DP sciences subjects
2. acquire and apply a body of knowledge, methods, tools and techniques that characterize science
3. develop the ability to analyse, evaluate and synthesize scientific information and claims
4. develop the ability to approach unfamiliar situations with creativity and resilience
5. design and model solutions to local and global problems in a scientific context
6. develop an appreciation of the possibilities and limitations of science
7. develop technology skills in a scientific context
8. develop the ability to communicate and collaborate effectively
9. develop awareness of the ethical, environmental, economic, cultural and social impact of science.

How it’s assessed

DP Biology is assessed at both Standard Level and Higher Level through a mix of external examinations and an internally assessed scientific investigation, with SL and HL following the same overall structure even though the papers differ in length and demand at each level. Paper 1 is weighted at 36% of the final grade and draws on the full breadth of the syllabus through short-answer and data-based questions; Paper 2 is weighted at 44% and includes short-answer and extended-response questions requiring more sustained scientific writing. Together, these two papers make up 80% of the final mark, with the exams differing in length and mark allocation between SL and HL rather than in this weighting split.

The remaining 20% comes from the internal assessment – an individual scientific investigation designed, carried out and written up by the student, culminating in a report of no more than 3,000 words. This sits alongside, but is separate from, the interdisciplinary collaborative sciences project that DP Biology students complete together with peers from other group 4 subjects; the collaborative project builds investigative skills, but it is the individually written scientific investigation that is formally graded.

The four syllabus themes

DP Biology’s content is organised into four themes rather than a strict linear sequence of biological levels, and it helps to see how they relate before studying any one in depth. Theme A, Unity and diversity, asks what all living things have in common and where their diversity comes from, covering topics such as the properties of water, nucleic acid structure, and evolution and speciation. Theme B, Form and function, connects biological structure at every scale to the job that structure performs, from macromolecules through to how an organism’s form suits its ecological niche. Theme C, Interaction and interdependence, moves from individual organisms to how living systems interact – internally through cell signalling and body-system integration, and externally through population ecology and the transfer of energy and matter through food webs. Theme D, Continuity and change, is the largest theme by teaching hours at both levels and covers how genetic information and traits persist and change across generations, from DNA replication and cell division through to natural selection. Because Paper 2’s data-based and extended-response questions are set across the whole syllabus, strong preparation involves drawing connections between themes – cell respiration and photosynthesis in Theme C, for instance, both depend on concepts introduced in Theme B’s membranes and organelles content – rather than revising each theme as an unconnected block.

The scientific investigation in more depth

The individually written scientific investigation that makes up 20% of the final grade requires a student to identify a research question, design and carry out an appropriate investigation, collect and process data, and evaluate the investigation’s methodology and conclusions, all within a report of no more than 3,000 words. Because this component is internally assessed by the student’s own teacher and then externally moderated, the investigation’s quality depends heavily on the research question being genuinely testable within the resources available to the student, rather than on the ambition of the topic chosen – a well-designed, carefully executed investigation into a modest, clearly answerable question typically scores more highly than an ambitious one that cannot be properly controlled or replicated.

SL and HL compared

Recommended teaching time for syllabus content is 110 hours at SL and 180 hours at HL, with a further 40 hours at SL and 60 hours at HL devoted to the experimental programme, the collaborative sciences project and the individual scientific investigation together. The extra HL teaching time is spent on sub-topics marked HL-only across all four themes, such as the origins of cells and classification and cladistics in Theme A, muscle and motility in Theme B, chemical signalling in Theme C, and gene expression in Theme D – content that carries extra weight in both Papers 1 and 2 and is, in practice, the material most often under-revised by HL students who default to SL-level depth out of habit rather than deliberately tracking which content is genuinely additional to their level.

Source

International Baccalaureate Organization, Biology subject brief (Diploma Programme), January 2022.