HSC Exam Practice

Sample response. A genotype is the genetic makeup of an organism — its combination of alleles. A phenotype is the observable characteristics of an organism (e.g. height, eye colour, enzyme activity).

Marking notes. 1 mark for defining genotype (allele combination / genetic makeup); 1 mark for defining phenotype (observable characteristics).

Sample response. Acceptable categories with roles include: enzymes — catalyse chemical reactions in metabolic pathways; structural proteins — provide support and strength to tissues (e.g. collagen); transport proteins — move substances across membranes or through the body; receptor proteins — bind signalling molecules so cells can respond; antibodies — recognise foreign molecules in immune defence.

Marking notes. 1 mark per correctly named category paired with a correct role (max 3). A correct category without a role, or vice versa, scores 0 for that entry.

Sample response. A protein is a chain of amino acids folded into a specific three-dimensional shape. The amino acid sequence determines how the protein folds. If the sequence changes (e.g. a substitution), the protein's shape can also change, and because function depends on shape (such as the fit of an enzyme's active site with its substrate, or a receptor's binding pocket with a signal molecule), function can be reduced, altered or lost.

Marking notes. 1 mark for stating that amino acid sequence determines shape / folding; 1 mark for stating that function depends on shape; 1 mark for explaining the mechanism by which an altered sequence alters function (e.g. active site mis-fits substrate, receptor cannot bind signal).

Sample response. The pathway is genotype → protein → biological effect → phenotype. The genotype encodes the amino acid sequence of proteins. Proteins fold into shapes that determine their function (catalysis, transport, signalling, support, defence). Protein activity produces biological effects in cells and organisms. Those effects accumulate into the observable phenotype.

Marking notes. 1 mark for naming all four stages in correct order; 1 mark for linking genotype to protein via amino acid sequence; 1 mark for linking protein activity to biological effect and then to phenotype.

Sample response. Phenotype is not determined by genes alone because environmental factors can influence how a characteristic is expressed even when genotype stays the same. For example, two individuals with similar genetic potential for height can reach different adult heights if their childhood nutrition differs: nutrition affects whether the gene-encoded growth proteins have the raw materials to act fully. The environment does not normally change the DNA sequence; it modifies expression of the phenotype.

Marking notes. 1 mark for stating that environment can influence phenotypic expression without changing genotype; 1 mark for naming a valid environmental factor and trait (e.g. nutrition / height, temperature / Himalayan rabbit fur, soil pH / hydrangea colour, sun exposure / skin pigmentation); 1 mark for explaining the mechanism by which the environment acts (e.g. limits substrate for growth proteins, alters enzyme activity).

Sample response (a). In every twin pair, the well-nourished twin is taller as an adult than the chronically malnourished twin. The within-pair difference ranges from approximately 8 cm (Pair 2: 173 vs 165) to approximately 15 cm (Pair 1: 176 vs 161), with Pair 3 differing by approximately 13 cm (181 vs 168). The pattern is consistent across pairs despite each pair sharing an identical genotype.

Sample response (b). Because each pair shares one genotype, both twins inherit the same alleles encoding growth-related proteins (e.g. growth hormone, growth-hormone receptors, structural collagen, enzymes of bone formation, transport proteins delivering nutrients). The chronically malnourished twin lacks the amino acids and energy needed for these proteins to act fully during growth, so the biological effect (bone and tissue growth) is reduced and the adult phenotype is shorter. The well-nourished twin's growth proteins act under sufficient resources, so genetic potential is more fully expressed. The environment acts at the protein-activity / biological-effect step of the genotype → protein → biological effect → phenotype pathway, without changing the underlying genotype.

Marking notes. Part (a) — 1 mark for identifying that the well-nourished twin is taller in every pair; 1 mark for quoting at least one supporting figure from the data (e.g. 15 cm difference in Pair 1). Part (b) — 1 mark for identifying that shared genotype rules out genetic differences as the cause; 1 mark for linking nutrition to growth-protein activity / biological effect; 1 mark for explicitly placing environment at the expression step of the genotype → protein → biological effect → phenotype pathway.

Sample response. The claim that phenotype is fully determined by genotype overstates the role of genes. Genotype is essential — it encodes the amino acid sequences of the proteins (enzymes, structural, transport, receptor and antibody proteins) that carry out almost every biological process. The lesson's pathway captures this: genotype → protein → biological effect → phenotype. A change in amino acid sequence can change protein shape, alter function and so change phenotype, which shows that genes do exert real and necessary influence over traits. However, phenotype also depends on how that gene-encoded protein machinery actually operates inside a living organism, which is environment-sensitive. A clear example is adult human height: monozygotic twins share an identical genotype, yet a twin raised with chronic childhood malnutrition is typically 5–15 cm shorter as an adult than the well-nourished co-twin, because the growth-related proteins do not have the amino acids and energy needed to act fully. Other examples include hydrangea flower colour shifting with soil pH despite identical plant genotype, and Himalayan rabbits developing darker fur at cooler body extremities because a temperature-sensitive enzyme is more active there. In every case, the environment does not change the DNA sequence; it modifies the activity of gene-encoded proteins and therefore the biological effect, altering the phenotype that is expressed. The claim is therefore rejected as overstated: phenotype is the product of genotype acting through protein function, modified by environmental influence on expression — a gene-environment interaction, not a purely genetic readout.

Marking notes. 1 mark — defines genotype and phenotype clearly. 1 mark — states the genotype → protein → biological effect → phenotype pathway. 1 mark — explains how protein function (and therefore phenotype) depends on amino acid sequence / shape. 1 mark — names at least one valid environmental factor + trait (e.g. nutrition / height, soil pH / hydrangea colour, temperature / Himalayan rabbit fur, sun exposure / skin pigmentation). 1 mark — explicitly states that environment does not normally change genotype but influences phenotypic expression. 1 mark — places the environment's action at a specific step of the pathway (protein activity / biological effect). 1 mark — reaches an explicit evaluative judgement that rejects "fully determined by genotype" and frames phenotype as a gene-environment interaction.