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IB Biology SL B4.2 Ecological Niches Questions

Practise IB Biology SL B4.2 by comparing niches, habitats, resource use, nutrition and environmental requirements with evidence.

Syllabus
First assessment 2025
Course
Biology SL
Level
SL

Exam points

  • Define an ecological niche as a species’ role, then compare species by habitat, resources and biotic or abiotic interactions.
  • Identify oxygen availability as a survival requirement for obligate aerobes in an environmental scenario.
  • Distinguish autotrophic from heterotrophic nutrition and explain how photosynthetic prokaryotes released oxygen into the early atmosphere.
  • Identify holozoic nutrition from ingestion and internal digestion, including evidence that distinguishes it from external saprotrophic digestion.
  • Classify Euglena or other named protists as mixotrophs when evidence shows both photosynthesis and heterotrophic feeding.
  • Identify fungi or bacteria as saprotrophs in food-web evidence, and explain external digestion, decomposition and nutrient recycling.
  • Identify methanogens as methane-producing Archaea and relate them to anaerobic conditions or habitats; identify halophile habitats from salt evidence.
  • Compare tooth-count, jaw and molar evidence across named Hominidae fossils, then relate dentition trends to dietary change.
  • Identify herbivore feeding adaptations such as chewing mouthparts, grinding teeth, long guts or cellulase-producing microbes.
  • Explain how prey camouflage, chemical mimicry or shell armour—and predator or prey morphology—change detection, attack or predation success.
  • Interpret chlorophyll and leaf-nitrogen data across light conditions, and explain how greater leaf chlorophyll supports light harvesting in low light.
  • Distinguish fundamental from realized niches and use interaction evidence to explain why a species occupies a narrower range.
  • Explain competitive exclusion and interpret Paramecium or other niche-overlap data to identify which species is excluded or restricted.

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: 6]

Ecologists studied the distribution of five species of insectivorous wood warblers of the genus Dendorica living on different parts of coniferous trees in mature forests.

Figure for Question 1 — IB Biology SL

Question (a)

(a)

Outline the principle of competitive exclusion

[ 2 ]

Question (b)

(b)

Other than position in the tree, suggest two ways in which the niches of the warblers in the ecosystem may differ.
1:
2:

[ 2 ]

Question (c)

(c)

The diagram shows the realized niches of the five species of warbler. Suggest how the fundamental niche of D. castanea might differ from its realized niche.

[ 2 ]

Question 2

[Maximum number: 1]

A student set up a 20 -metre transect line along a rocky shore and measured the abundance of seven species of seaweeds (A-G) at 21 different sampling stations at fixed distances. The kite diagram represents the species abundance data across the 20 metres.

Figure for Question 2 — IB Biology SL

Seaweeds are obligate aerobes. Describe an environmental condition required for seaweed survival.

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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