Option B

Option B : Biochemistry


Teenagers have a natural curiosity about who they are and how their body functions. They want to know the answers to questions like, ‘How is light converted into electrical signals in the eye?’, ‘Why do fatty foods increase the risk of heart disease?’ and ‘How can genetic information be stored in DNA?’ Option B contains the answers to all these questions and many more. It is one of the more popular options and students generally enjoy studying it as they can very easily relate to the material it covers.

Although some of the content of the option needs to be memorized a surprising amount can be deduced once the underlying theory is understood. The structures of any complex molecules that are required are given in Sections 31, 33, 34 and 35 in the IB Chemistry data booklet so the emphasis is more on recognising important functional groups contained within them and on their chemical properties and reactions rather than on recall. In terms of methodology there is some similarity with Option D: Medicinal chemistry as both involve reactions of chemical substances within the body. Much of the chemistry contained within the option can be a useful addition to students who are also studying IB Biology as one of their six diploma subjects but there is actually very little overlap with the Biology syllabus. For this reason you should warn students not to answer questions on Option B when they take the Paper 3 examination unless they have actually studied the option. Knowledge of biology on its own will not be sufficient to gain many, if any, marks in Option B. It might be tempting to think that, like Option D, this option would also be a useful preparation to those who want to go on and study medicine. In reality it probably does not make much difference which one of the four options students study now that they all contain the same four strands of quantitative, analytical, environmental and organic chemistry. It might be worth mentioning though that the only analytical references in the core part of this topic are to paper chromatography and electrophoresis as ways of identifying amino acids. Using spectroscopy for analysis does not appear until the assay of proteins using UV-Vis spectroscopy in the Higher Level part of the option. Similarly the only clear reference to quantitative chemistry in the core part of the option is the determination of the iodine number for unsaturated fats. This presents an interesting challenge each year to the people who set the external Standard Level Paper 3 Section B questions.

If you have previously taught the Human Biochemistry option for the old programme then you will find much that is similar although there are some notable differences. The core part of this option basically gives an introduction to biochemistry (including metabolism, photosynthesis and respiration) then looks at the chemistry of proteins and enzymes, carbohydrates, lipids, vitamins and biochemistry and the environment (including green chemistry and xenobiotics). The additional Higher Level material covers the characteristics of enzymes (including enzyme kinetics, buffer calculations and the assay of proteins by UV-Vis spectroscopy) the chemical explanations behind the functioning of nucleic acids (including the genetic code and genetically modified foods), biological pigments and stereochemistry in biomolecules.

There is considerable scope for practical work although none of it is mandatory. You could for example, determine the iodine number of an unsaturated fat, perform paper chromatography on different food colourings (or a hydrolysed protein), assay the concentration of a protein in solution using visible spectroscopy or analyse a fruit (or fruit juice) for its vitamin C content.


The linked pages basically follow the syllabus and take each sub-topic in turn. They start with ‘Pause for thought’, which aims to stimulate and get you (and your students) thinking about some aspect of the topic. A box follows this on how Nature of Science is addressed by the sub-topic, then learning outcomes (‘understandings’ and ‘applications and skills’), clarifications, the international-dimension, teaching tips, key vocabulary and other resources (including videos and the relevant pages in my Study Guide) and suggestions for homework. Each sub-topic has an embedded slide gallery which covers all the syllabus content and contains tasks with worked answers. For all of the topics there is an attached link leading to a separate page with original questions (together with worked answers) on the topic. Although the IB does not test the options using multiple choice questions I have also provided a quiz containing ten questions with the answers explained for each sub-topic as it provides an efficient and quick way for students to test both their knowledge and understanding.

Introductory video

A high definition video by Frank Gregorio to introduce students to the science of biochemistry, which is well worth showing.

  Introduction to biochemistry

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