# Explain how the concept of carrying capacity influences the growth dynamics of a population experiencing logistic growth.

> IB DP Biology Higher Level (2023 syllabus) — C4.1 Populations and communities · Explain · 4 marks

> A bacterial population is introduced into a nutrient-rich culture medium. Initially, the population grows rapidly, but growth rate slows and eventually stabilises at a maximum population size.

## Mark scheme (4 marks)

1. Carrying capacity (K) is the maximum population size that an environment can sustainably support, limited by available resources.
2. When population size is well below K, resources are plentiful and per capita birth rate exceeds death rate, so the population grows rapidly (approximately exponential / J-shaped growth).
3. As population size approaches K, intraspecific competition for limiting resources intensifies, reducing per capita birth rate and/or increasing death rate, so the rate of population growth declines.
4. At K, birth rate equals death rate, so net population growth rate is zero and population size stabilises, producing the characteristic S-shaped (sigmoidal / logistic) growth curve.

## Key terms

- [carrying capacity](https://www.gradenine.co.uk/glossary/carrying-capacity)
- [logistic growth](https://www.gradenine.co.uk/glossary/logistic-growth)

## Related

- [Revision notes for IB DP Biology Higher Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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