Syllabus Edition

First teaching 2023

First exams 2025

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Ecological Niches (HL IB Biology)

Exam Questions

14 mins8 questions
1a3 marks

Spirulina (Athrospira platensis) is a blue-green alga that is consumed for its nutritional benefits, which are considered to be good for oral health, eye health and maintaining healthy blood pressure, amongst other benefits.

The graph shows the results from an investigation into the optimum growing conditions for Spirulina. 

Spirulina was grown in a glucose medium and exposed to different intensities of light. The same method was carried out with an autotrophic species of alga.

yLl0Pszs_spirulina-growth-sq

Explain how the results show that Spirulina is a mixotrophic organism.

1b2 marks

Compare the growth rate of Spirulina and the autotrophic algal species when light intensity was increased from 0 to 200 lx.

1c2 marks

Suggest how Spirulina may be adapted to function as a mixotroph.

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