Probably the most daunting questions IB Biology students have to answer are the extended response questions.
They are not essays, but they do require a little structure.
This post shares helpful ideas about how to approach these questions.
Reading the question carefully is the first essential thing, but writing precisely is also key.
Keeping each point short avoids the risk that a mistake in one detail affects two points.
Beginning each point on a separate line makes the different points more visible to the examiner. (As I've done in this introduction!)

Succeeding with extended response questions.

These slides give helpful ideas about answering extended response questions.

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As these slides show, there are some simple ways to improve he quality of written answers . Whatever the topic these points will help you write a better extended answers and archived higher marks.