B4.2 Ecological niches

Question 1

B4.2.1—Ecological niche as the role of a species in an ecosystem

Answer 1

Include the biotic and abiotic interactions that influence growth, survival and reproduction, including how
a species obtains food.

Question 2

B4.2.2—Differences between organisms that are obligate anaerobes, facultative anaerobes and obligate
aerobes

Answer 2

Limit to the tolerance of these groups of organisms to the presence or absence of oxygen gas in their
environment.

Question 3

B4.2.3—Photosynthesis as the mode of nutrition in plants, algae and several groups of photosynthetic
prokaryotes

Answer 3

Details of different types of photosynthesis in prokaryotes are not required.

Question 4

B4.2.4—Holozoic nutrition in animals

Answer 4

Students should understand that all animals are heterotrophic. In holozoic nutrition food is ingested,
digested internally, absorbed and assimilated.

Question 5

B4.2.5—Mixotrophic nutrition in some protists

Answer 5

Euglena is a well-known freshwater example of a protist that is both autotrophic and heterotrophic, but
many other mixotrophic species are part of oceanic plankton. Students should understand that some
mixotrophs are obligate and others are facultative.

Question 6

B4.2.6—Saprotrophic nutrition in some fungi and bacteria

Answer 6

Fungi and bacteria with this mode of heterotrophic nutrition can be referred to as decomposers

Question 7

B4.2.7—Diversity of nutrition in archaea

Answer 7

Students should understand that archaea are one of the three domains of life and appreciate that they are
metabolically very diverse. Archaea species use either light, oxidation of inorganic chemicals or oxidation
of carbon compounds to provide energy for ATP production. Students are not required to name examples.

Question 8

B4.2.8—Relationship between dentition and the diet of omnivorous and herbivorous representative
members of the family Hominidae

Answer 8

Application of skills: Students should examine models or digital collections of skulls to infer diet from the
anatomical features. Examples may include Homo sapiens (humans), Homo floresiensis and Paranthropus
robustus.
NOS: Deductions can be made from theories. In this example, observation of living mammals led to
theories relating dentition to herbivorous or carnivorous diets. These theories allowed the diet of extinct
organisms to be deduced.

Question 9

B4.2.9—Adaptations of herbivores for feeding on plants and of plants for resisting herbivory

Answer 9

For herbivore adaptations, include piercing and chewing mouthparts of leaf-eating insects. Plants resist
herbivory using thorns and other physical structures. Plants also produce toxic secondary compounds in
seeds and leaves. Some animals have metabolic adaptations for detoxifying these toxins.

Question 10

B4.2.10—Adaptations of predators for finding, catching and killing prey and of prey animals for resisting
predation

Answer 10

Students should be aware of chemical, physical and behavioural adaptations in predators and prey.

Question 11

B4.2.11—Adaptations of plant form for harvesting light

Answer 11

Include examples from forest ecosystems to illustrate how plants in forests use different strategies to reach
light sources, including trees that reach the canopy, lianas, epiphytes growing on branches of trees,
strangler epiphytes, shade-tolerant shrubs and herbs growing on the forest floor.

Question 12

B4.2.12—Fundamental and realized niches

Answer 12

Students should appreciate that fundamental niche is the potential of a species based on adaptations and
tolerance limits and that realized niche is the actual extent of a species niche when in competition with
other species.

Question 13

B4.2.13—Competitive exclusion and the uniqueness of ecological niches

Answer 13

Include elimination of one of the competing species or the restriction of both to a part of their
fundamental niche as possible outcomes of competition between two species.