Syllabus Edition

First teaching 2023

First exams 2025

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Populations in Ecosystems (HL IB Biology)

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Naomi H

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Naomi H

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Populations

  • A population can be defined as:

A group of organisms of the same species living in an area at one time

  • Members of a population interact with each other and can breed together
  • A population can be isolated from other populations of the same species due to living in a different area
  • This isolation means that members of separate populations cannot breed together and gene exchange cannot take place between them
gannet colony

CC BY 2.0, via Wikimedia Commons

Gannets are sea birds. Populations gather on sea cliffs to breed during nesting season.

Examiner Tip

The IB specification uses the phrase 'reproductive isolation' here to describe two populations of the same species that are separate from each other, i.e. isolated, and that are not interbreeding. While this does make sense in this context, it is worth noting that the term reproductive isolation is more frequently used among biologists to describe the point in the speciation process at which two populations have diverged to become two different species.

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Naomi H

Author: Naomi H

Expertise: Biology

Naomi graduated from the University of Oxford with a degree in Biological Sciences. She has 8 years of classroom experience teaching Key Stage 3 up to A-Level biology, and is currently a tutor and A-Level examiner. Naomi especially enjoys creating resources that enable students to build a solid understanding of subject content, while also connecting their knowledge with biology’s exciting, real-world applications.