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IB Biology HL B4.2 Ecological Niches Questions

Practise IB Biology HL B4.2 by comparing ecological niches and feeding strategies, explaining adaptations, and analysing competition between species.

Syllabus
First assessment 2025
Course
Biology HL
Level
HL

Exam points

  • Define a species’ niche by its habitat, feeding, activity and interactions, then compare ecological roles across species.
  • Distinguish oxygen-requiring aerobes, oxygen-intolerant anaerobes and facultative anaerobes that switch respiration strategy.
  • Identify photoautotrophs and relate cyanobacterial photosynthesis to oxygen production in the atmosphere.
  • Explain holozoic ingestion and internal digestion, and classify consumers such as nectar- and insect-feeding hummingbirds.
  • Explain mixotrophy by combining photosynthesis and heterotrophic feeding in named organisms such as Euglena.
  • Explain saprotrophic external digestion and nutrient recycling, and distinguish saprotrophs from detritivores.
  • Compare archaeal energy and carbon sources, and explain methanogenesis from biomass under anaerobic fermenter conditions.
  • Compare hominid skulls by jaw projection and tooth size as evidence of dietary dentition differences.
  • Explain herbivore feeding adaptations and plant defenses such as chewing mouthparts, aphid stylets, spines, stinging hairs or toxins.
  • Identify predator or prey adaptations such as camouflage, mimicry and warning colouration from organism examples.
  • Distinguish fundamental from realized niches and explain how biotic interactions, including competition, narrow the realized niche.
  • Explain competitive exclusion when species overlap in a limiting resource, and predict replacement or realized-niche change.

Covered syllabus points

B4.2.1—Ecological nicheB4.2.2—Oxygen toleranceB4.2.3—Photosynthesis as nutrition modeB4.2.4—Holozoic nutritionB4.2.5—Mixotrophic nutritionB4.2.6—Saprotrophic nutritionB4.2.7—Diversity in archaeaB4.2.8—Dentition and diet in Family HominidaeB4.2.9—Herbivore and plant adaptationsB4.2.10—Predator and prey adaptationsB4.2.11—Plant form for light harvestingB4.2.12—Fundamental vs. realized nicheB4.2.13—Competitive exclusion

Question 1

[Maximum number: 2]

Outline what is meant by the niche concept.

Question 2

[Maximum number: 2]

Marine sediments form at the bottom of oceans. These sediments contain organic material from the surface waters. Scientists analysed samples drilled from the floor of the north Pacific Ocean, representing 86 million years of sedimentation. Graph A shows the data for oxygen concentrations in 28 metres of sediment and graph B shows the oxygen consumption per cell in 22 metres of sediment measured in femtomoles ( fmol=10−15 mol\mathrm{fmol}=10^{-15} \mathrm{~mol} ).

Figure for Question 2 — IB Biology HL

Suggest reasons for the differences in oxygen consumption between the cells at 2 metres and at 22 metres.

Question 3

[Maximum number: 3]

There is evidence that prokaryotes were responsible for changes in the atmospheric gases 3.5 billion years ago. Outline the role of bacteria in producing an oxygen-rich atmosphere.

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