B4.2 Ecological niches
Practice exam-style IB Biology questions for Ecological niches, aligned with the syllabus and grouped by topic.
Question 1
An ecological niche is best defined as the
A.
role of a species in an ecosystem, including its resources and interactions.
B.
sequence of organisms transferring energy by feeding.
C.
number of individuals of a species in a community.
D.
place where a species is most commonly found.
Question 2
A bacterial species grows in oxic water but can also survive in anoxic sediment. What type of organism is it?
A.
Facultative anaerobe
B.
Obligate anaerobe
C.
Photosynthetic prokaryote
D.
Obligate aerobe
Question 3
What is the mode of nutrition in which light energy is used to synthesize organic carbon compounds from carbon dioxide?
A.
Saprotrophic nutrition
B.
Photosynthesis
C.
Holozoic nutrition
D.
Chemotrophy
Question 4
Which sequence correctly describes holozoic nutrition in animals?
A.
Absorption → photosynthesis → ingestion → egestion
B.
Carbon fixation → absorption → internal digestion → egestion
C.
External digestion → absorption → ingestion → assimilation
D.
Ingestion → internal digestion → absorption → assimilation
Question 5
What feature distinguishes saprotrophic nutrition from holozoic nutrition?
A.
Saprotrophs ingest food and digest it in a gut.
B.
Saprotrophs fix carbon dioxide using light energy.
C.
Saprotrophs obtain energy only from inorganic chemicals.
D.
Saprotrophs digest food externally before absorbing soluble products.
Question 6
Define ecological niche.
[1]
State one biotic factor and one abiotic factor that could be part of the niche of a freshwater snail.
[1]
Question 7
A protist grows using photosynthesis in light but obtains organic compounds heterotrophically in darkness. What term describes this nutritional strategy?
A.
Saprotrophic
B.
Herbivorous
C.
Mixotrophic
D.
Obligate aerobic
Question 8
Broad molars with large grinding surfaces and a robust jaw in a hominid skull provide strongest evidence for a diet rich in
A.
fibrous plant material.
B.
nectar.
C.
blood taken from prey.
D.
whole fish swallowed without chewing.
Question 9
Which row correctly describes the diversity of nutrition in archaea?
A.
Archaea only obtain energy by ingesting other cells.
B.
Archaea may use light, inorganic chemicals or carbon compounds as energy sources.
C.
All archaea are holozoic heterotrophs.
D.
All archaea photosynthesize and release oxygen.
Question 10
A prey species forms dense schools when predators are nearby. What type of adaptation is this?
A.
Physical predator adaptation
B.
Behavioural prey adaptation
C.
Metabolic plant adaptation
D.
Chemical predator adaptation
Question 11
A woody plant germinates on the forest floor but climbs other trees to place its leaves in high light. It does not take food from the supporting tree. What plant form is described?
A.
Saprotroph
B.
Shade-tolerant herb
C.
Liana
D.
Obligate anaerobe
Question 12
Piercing mouthparts in a leaf-feeding insect are best adapted for
A.
secreting enzymes onto dead leaves.
B.
absorbing light on shaded branches.
C.
penetrating plant tissues and sucking liquid food.
D.
biting and grinding pieces from the leaf blade.
Question 13
State the oxygen requirement of an obligate aerobe.
[1]
Distinguish between an obligate anaerobe and a facultative anaerobe.
[1]
Question 14
Outline photosynthesis as a mode of nutrition.
[1]
State two groups of organisms that include photosynthetic species.
[1]
Question 15
State why animals are described as heterotrophs.
[1]
Outline the processes of absorption and assimilation in holozoic nutrition.
[1]
State what is removed by egestion.
[1]
Question 16
State the type of organisms that commonly show saprotrophic nutrition.
[1]
Outline how saprotrophic nutrition contributes to nutrient cycling.
[1]
Question 17
A sealed column of pond mud and water was exposed to light. After several weeks, three microbial bands formed at different depths.
Identify the band most likely to contain obligate aerobes.
[1]
Describe the relationship between depth and oxygen availability shown.
[1]
Suggest why facultative anaerobes could be found over a wider depth range than obligate anaerobes.
[1]
Question 18
What distinguishes a realized niche from a fundamental niche?
A.
The realized niche is the actual niche occupied when competition and other interactions occur.
B.
The realized niche includes only abiotic tolerance limits.
C.
The realized niche is always larger than the fundamental niche.
D.
The realized niche is the potential niche in the absence of competitors.
Question 19
An insect species feeds successfully on leaves containing a toxic secondary compound but grows poorly on undefended leaves from several other plant species. What is the most likely explanation?
A.
The insect uses photosynthesis as its main nutrition.
B.
The insect has a specialized detoxification adaptation for one plant toxin.
C.
The insect is an obligate aerobe and requires oxygen.
D.
The insect has a realized niche larger than its fundamental niche.
Question 20
Two species with completely overlapping niches are grown together in a stable habitat with one limiting resource. Species X consistently uses the resource more efficiently. What is the most likely long-term outcome?
A.
Species Y is eliminated by competitive exclusion.
B.
Both species expand beyond their fundamental niches.
C.
Species X becomes an obligate anaerobe.
D.
Both species become autotrophic.
Question 21
What distinguishes a facultative mixotroph from an obligate mixotroph?
A.
A facultative mixotroph cannot use carbon dioxide.
B.
A facultative mixotroph can grow using either autotrophic or heterotrophic nutrition, depending on conditions.
C.
A facultative mixotroph must use both autotrophic and heterotrophic nutrition for growth.
D.
A facultative mixotroph is always an animal.
Question 22
A generalist predator changes from eating large insects to small fish after a dry season reduces insect abundance. What advantage of versatility is shown?
A.
Dependence on one specialized resource
B.
Greater resilience when resource availability changes
C.
Restriction to a narrower realized niche
D.
Complete avoidance of all competition
Question 23
A culture of Euglena is kept in light for one week and then transferred to darkness with dissolved organic compounds present.
State the nutritional term used for Euglena.
[1]
Compare the inputs used by Euglena in light and in darkness.
[1]
Question 24
The visual shows simplified dentition of two hominid skulls.
Identify which skull is more likely to have a plant-rich diet.
[1]
Explain two dental features that support this inference.
[1]
State one additional type of evidence that could strengthen a deduction about diet in an extinct hominid.
[1]
Question 25
Define fundamental niche.
[1]
Distinguish realized niche from fundamental niche using competition.
[1]
Question 26
State the domain to which archaea belong.
[1]
Explain the nutritional diversity of archaea in terms of energy sources for ATP production.
[1]
Question 27
Distinguish chewing mouthparts from piercing mouthparts in leaf-feeding insects.
[1]
Explain how a toxic secondary compound in leaves can reduce herbivory.
[1]
Question 28
For each adaptation, classify it as chemical, physical or behavioural.
Venom injected by a predator.
[1]
Camouflage in a prey insect.
[1]
Cooperative hunting by wolves.
[1]
Question 29
State one advantage of niche specialization.
[1]
Explain one disadvantage of specialization compared with a generalist strategy.
[1]
Question 30
Compare saprotrophic and holozoic nutrition in terms of where digestion occurs.
[1]
State one input and one output of saprotrophic nutrition.
[1]
Question 31
Cultures of a mixotrophic protist were grown under four treatments differing in light and availability of dissolved organic compounds. Growth was measured after six days.
Identify the treatment with the greatest growth.
[1]
Compare growth in light without organic compounds and darkness with organic compounds.
[1]
Explain why growth may occur in both of these treatments.
[1]
Question 32
Measurements were taken from three hominid skulls with unknown diets.
| Skull | Molar grinding area / cm² | Canine projection / mm | Jaw robustness / mm |
|---|---|---|---|
| A | 8.7 | 4.8 | 23.5 |
| B | 14.6 | 1.9 | 32.8 |
| C | 10.1 | 6.1 | 25.4 |
Identify the skull most likely to have the most herbivorous diet.
[1]
State two measurements that support your answer.
[1]
Explain why this conclusion is a deduction rather than a direct observation.
[1]
Question 33
Two freshwater plants were grown separately and together along a water-depth gradient.
State which curve represents the fundamental niche of species P.
[1]
Describe the change in the distribution of species P when grown with species Q.
[1]
Explain the difference between the two distributions of species P.
[1]
Question 34
Larvae of a moth were fed on three plant species. One plant contained a toxic secondary compound. Some larvae carried an allele associated with detoxification.
Identify the larval genotype with highest survival on the toxic plant.
[1]
Compare survival of detoxifying and non-detoxifying larvae across the plant species.
[1]
Evaluate whether detoxification is more likely to be a specialized or versatile adaptation in this case.
[1]
Question 35
Light intensity was measured at different heights in a forest. The abundance of four plant forms was also recorded.
| Height zone | Height / m | Light / % full sun | Canopy trees / % records | Lianas / % records | Epiphytes / % records | Shade herbs / % records |
|---|---|---|---|---|---|---|
| Forest floor | 0–2 | 2 | 8 | 5 | 1 | 86 |
| Understorey | 2–10 | 8 | 22 | 28 | 7 | 43 |
| Sub-canopy | 10–20 | 35 | 34 | 31 | 25 | 10 |
| Canopy | 20–35 | 78 | 45 | 24 | 29 | 2 |
Identify the plant form most abundant at the lowest light intensity.
[1]
Describe the relationship between height and light intensity.
[1]
Explain why lianas and epiphytes can be abundant above the forest floor without investing as much in self-support as canopy trees.
[1]
State one limitation faced by epiphytes.
[1]
Question 36
In a tropical forest, several plant forms harvest light in different ways.
Outline how a liana gains access to light.
[1]
Explain one advantage and one limitation of an epiphyte growing on tree branches.
[1]
State how shade-tolerant herbs differ from canopy trees in their light-harvesting strategy.
[1]
Question 37
Two species of intertidal snail eat the same algae. When each species is kept alone, both occupy the full shore height range. When kept together, one species occurs only on the upper shore and the other only on the lower shore.
State the ecological process causing this pattern.
[1]
Suggest why both species persist rather than one being eliminated.
[1]
State what this shows about their realized niches.
[1]
Question 38
A predator species has forward-facing eyes, sharp claws and stalks prey before a rapid attack.
Identify one physical adaptation for finding prey.
[1]
Identify one physical adaptation for catching or killing prey.
[1]
Suggest why stalking behaviour may be favoured by natural selection.
[1]
Question 39
Two species of flour beetle were grown in containers with the same limiting food resource. Population size was recorded when each species was grown alone and when both were grown together.
Identify the species that was excluded when both were grown together.
[1]
Compare the population trends of the two species in the mixed culture.
[1]
Suggest why the result is an example of competitive exclusion.
[1]
Question 40
A prey fish was observed in tanks with and without a predator scent. Schooling density and individual feeding rate were recorded.
| Water treatment | Schooling density / fish m^-3 | Feeding rate / items fish^-1 min^-1 |
|---|---|---|
| Control water | 18 | 6.4 |
| Predator scent | 42 | 3.1 |
Describe the effect of predator scent on schooling density.
[1]
Describe the effect of predator scent on feeding rate.
[1]
Suggest one benefit and one cost of the behavioural response shown.
[1]
Question 41
The foraging niche of three bird species was studied by recording prey size and feeding height.
Identify the pair of species with the greatest niche overlap in the two measured dimensions.
[1]
Explain why the graph shows only part of each species’ niche.
[1]
Suggest two other niche dimensions that could reduce competition between the pair identified.
[1]
Question 42
Outline photosynthesis as a mode of nutrition.
[1]
Compare photosynthetic, holozoic and saprotrophic nutrition in terms of inputs, processes and outputs.
[1]
Question 43
Distinguish between biotic and abiotic factors using one example of each.
[1]
Discuss why an ecological niche should not be described only as the habitat of a species.
[1]
Question 44
State the meaning of mixotrophic nutrition and give one example of a mixotroph.
[1]
Explain the ecological advantages and limitations of facultative and obligate mixotrophy.
[1]
Question 45
Two barnacle species were surveyed along a shore. Laboratory tolerance tests showed both species could survive a wider range of tidal heights than their field distributions suggested.
Identify which data set is most likely to represent the fundamental niche.
[1]
Compare the laboratory and field distributions for one species.
[1]
Evaluate the conclusion that competition restricts the realized niche of one species.
[1]
Question 46
Define fundamental niche and realized niche.
[1]
Explain how competition can lead to either competitive exclusion or restriction of realized niches.
[1]
Question 47
Outline two dental features used to infer diet in members of Hominidae.
[1]
Evaluate the use of dentition to deduce the diet of an extinct hominid.
[1]
Question 48
Distinguish between chewing and piercing mouthparts in leaf-feeding insects.
[1]
Compare adaptations of herbivores for feeding on plants with plant adaptations for resisting herbivory.
[1]
Question 49
Classify predator and prey adaptations as physical, chemical or behavioural, giving one example of each category.
[1]
Discuss how predator and prey adaptations are related to finding, catching and resisting capture.
[1]
Question 50
Outline two forest plant forms that increase access to light.
[1]
Evaluate the advantages and costs of different plant strategies for harvesting light in forests.
[1]
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