HSC Exam Practice

Sample response. An adaptation is an inherited characteristic that increases an organism’s fitness in a particular environment, and is the result of natural selection acting on heritable variation over many generations.

Marking notes. 1 mark for any two of: inherited; increases fitness; result of natural selection over generations. 2 marks for all three criteria clearly stated. Accept paraphrasing provided the three ideas are present.

Sample response. A structural adaptation is a physical feature of anatomy, for example, thorny devil skin grooves that channel dew toward the mouth. A physiological adaptation is an internal biochemical or functional process, for example, embryonic diapause in red kangaroos. A behavioural adaptation is an action pattern, for example, crepuscular activity in red kangaroos to avoid midday heat.

Marking notes. 1 mark per correctly defined type with a valid example. Accept any example from the lesson content for each type.

Sample response. Convergent adaptation occurs when unrelated organisms independently evolve similar traits in response to similar selection pressures in similar environments. For example, sharks (fish) and dolphins (mammals) both evolved streamlined bodies for efficient movement through water, despite being from completely different evolutionary lineages.

Marking notes. 1 mark for the concept (unrelated organisms; similar environments; independently evolved similar traits). 1 mark for a named example from the lesson (sharks/dolphins; cacti/euphorbias).

Sample response. (i) Acacia phyllodes, structural (physical feature of anatomy). (ii) Embryonic diapause, physiological (internal functional process). (iii) Crepuscular activity, behavioural (action pattern). Justification for one: Acacia phyllodes are structural because they are a physical modification of leaf shape, the phyllode is a flattened stem that acts like a leaf but has less surface area to reduce water loss, which is a change in body form rather than an internal process or action.

Marking notes. 1 mark for all three classified correctly. 1 mark for a valid justification of one classification that references whether the feature is anatomy, internal process, or action pattern.

Sample response. A biological adaptation must be an inherited characteristic, it must be encoded in the organism’s genes and passed to offspring through reproduction. A trait developed during an individual’s lifetime through exercise, experience or behaviour is a phenotypic change that is not heritable in the genetic sense, so it cannot be an adaptation. Adaptations result from natural selection acting on heritable variation across generations, not from changes an individual makes in response to its immediate needs.

Marking notes. 1 mark for identifying that adaptations must be inherited/heritable. 1 mark for explicitly stating that lifetime-acquired traits are not inherited and therefore do not qualify as adaptations.

Sample response. The thorny devil’s spines and skin grooves channel condensed dew or moisture from across its body surface toward the mouth [1]. In an arid environment where standing water is scarce, this structural feature increases fitness by allowing the thorny devil to collect and drink water from morning dew or wet sand, improving survival by reducing the risk of dehydration [1].

Marking notes. 1 mark for describing how the structural feature works (grooves/spines channel water to mouth). 1 mark for linking this to fitness increase in an arid environment (water collection; survival; dehydration prevention).

Sample response. The fact that the thorny devil possesses structural, physiological and behavioural adaptations simultaneously tells us that adaptations are not limited to one type and that organisms can be shaped by multiple selection pressures at once [1]. Different selection pressures in the arid environment (water scarcity, temperature extremes, predation risk) require different adaptive responses [1]. The presence of all three types together shows that natural selection acts across every aspect of an organism’s biology, anatomy, internal function and behaviour, and that all three categories can be equally important for survival [1].

Marking notes. 1 mark for noting that all three types can coexist in one organism. 1 mark for explaining that different selection pressures drive different adaptation types. 1 mark for synthesising: natural selection operates across all aspects of biology; no single type is inherently superior.

Sample response. Embryonic diapause is classified as a physiological adaptation because it is an internal biochemical/hormonal process that regulates embryo development from within the organism’s body [1]. It is not an observable physical body structure, nor is it a voluntary action or response pattern the kangaroo performs, it occurs internally through hormonal signalling and metabolic regulation, which are the defining features of physiological adaptations [1].

Marking notes. 1 mark for identifying it as an internal process/function. 1 mark for explicitly distinguishing it from structural (not body anatomy) and behavioural (not an action pattern), or explaining what makes it physiological (internal biochemical/hormonal regulation).

Sample response. The claim that similar features always indicate close evolutionary relationship is incorrect. Adaptations are inherited characteristics that increase fitness in a particular environment, resulting from natural selection over many generations. They arise because environments create selection pressures that favour certain traits, not because of shared ancestry.

Convergent adaptation occurs when unrelated organisms independently evolve similar traits in response to similar selection pressures. A classic example is the streamlined body shape seen in both sharks (Class Chondrichthyes, a fish) and dolphins (Class Mammalia, a mammal). Both are active aquatic predators, and efficient movement through water is a shared selection pressure. Each lineage independently evolved a streamlined, torpedo-shaped body because this shape reduces drag and improves swimming efficiency. Their structural similarity reflects a common environmental challenge, not a recent common ancestor.

A second example is cacti (Americas) and euphorbias (Africa): unrelated desert plants that independently evolved spines, reduced leaves and water-storing stems in response to the selection pressure of water scarcity in arid environments.

Appearance alone is therefore a weak basis for inferring evolutionary relatedness, because similar environments can repeatedly select for similar phenotypes in organisms with no close common ancestor. The strength of evidence for relatedness comes from combining multiple evidence types, including genetic analysis, not from structural similarity alone.

The claim is false: convergent adaptation demonstrates that similar features can arise independently in unrelated organisms, and similarity of appearance does not automatically indicate close ancestry.

Marking criteria.

• 1 mark Correct definition of adaptation including inherited, fitness increase, natural selection over generations.
• 1 mark Correct definition of convergent adaptation (unrelated organisms; similar environments; independently evolved similar traits).
• 1 mark Names at least one specific example from the lesson (sharks/dolphins; cacti/euphorbias).
• 1 mark Identifies the selection pressure for the named example (aquatic locomotion / water scarcity).
• 1 mark Explicitly states that similarity does not prove close ancestry and explains why (convergent adaptation in unrelated lineages).
• 1 mark Uses a second example or additional supporting evidence from the lesson.
• 1 mark Evaluates the strength of appearance alone as evidence for relatedness (weak; needs genetic/other evidence).
• 1 mark Reaches an explicit evaluative conclusion that the claim is false, with precise lesson vocabulary (convergent adaptation, selection pressure, fitness, heritable).