36 exam-style questions on Ecological niches — topic B4.2 of Form and function in the IB Biology syllabus — with answers and explanations. Samples below; the full set is free with an account.
Define the ecological niche of a species.
Answer: The functional role of a species in its community
A niche is a species' functional role, including its habitat, food sources, tolerance of abiotic conditions and interactions; the physical place alone is the habitat, not the niche.
Identify the mode of nutrition of an organism that secretes enzymes onto dead organic matter and absorbs the products of this external digestion.
Answer: Saprotrophic nutrition
Saprotrophs (e.g. many fungi and bacteria) secrete enzymes onto dead matter, digest it outside their cells and absorb the products; holozoic nutrition instead involves ingesting food and digesting it internally.
State which term describes heterotrophs that ingest food and digest it internally, such as most animals.
Answer: Holozoic organisms
Holozoic nutrition involves ingesting solid or liquid food, digesting it inside the body and absorbing the products; this is typical of animals.
Explain the difference between the fundamental niche and the realised niche of a species.
Answer: The fundamental niche is the full potential range; the realised niche is the smaller range occupied after competition
The fundamental niche is the potential niche set by tolerance to abiotic factors; interspecific competition and other biotic interactions usually restrict the species to a smaller realised niche.
In an experiment, two species of Paramecium grown separately both thrive, but when grown together one species dies out. Determine which principle this illustrates.
Answer: Competitive exclusion
Gause's Paramecium experiments demonstrated competitive exclusion: when two species have overlapping niches and limited resources, the superior competitor eliminates the other.
Suggest how two similar bird species feeding in the same tree can coexist despite overlapping niches.
Answer: They partition the resource, feeding in different parts
Resource partitioning (as in MacArthur's warblers) lets species divide a shared resource by space, time or food type, so their realised niches differ enough to allow coexistence.
That was 6 of 36 Ecological niches questions.
Practise all 36 freeSuggestAO3 · 3–8 marks
Propose a plausible solution, hypothesis or answer; there may be no single right one, but it must be reasoned.
OutlineAO2 · 1–4 marks
A brief account or summary: the main points in two or three sentences, no evaluation.
DistinguishAO2 · 1–4 marks
Make the difference clear for BOTH terms — a definition of one of them is only half an answer.
36 Ecological niches questions — free with an account. Spaced repetition, streaks and full exam simulations included.
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