Zadanie 9, Paper 2, maj 2026, TZ3, Biologia IB HL
Wzorowane na: Biology HL Paper 2, May 2026, TZ3, pytanie 9. Treść, dane i kontekst są zmienione; sprawdzane umiejętności, format i punktacja jak w oryginale.
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Zadanie
Polecenie
Inherited information is encoded in DNA and expressed in phenotypes.
(a) Draw a DNA segment containing two base pairs. Label its nucleotide components and the interactions between the bases.
(b) Describe how whole-genome sequencing can be used to infer relationships between species.
(c) Explain how inherited information and phenotypic plasticity contribute to observable traits.
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Odpowiedź z klucza
(a) A nucleotide is shown with phosphate, deoxyribose and a base each labelled at least once. ✔
Phosphate attachments correspond to the sugar C5 position and bases to C1. ✔
Two base pairs are linked by two or three dashed hydrogen-bond lines, with at least one hydrogen-bond label. ✔
Each strand contains two nucleotides; sugar pentagons on one strand face the opposite direction to those on the other strand, representing antiparallel backbones. ✔
(b) Sequencing determines an organism’s complete DNA base sequence, OR the genome is defined as the complete DNA sequence. ✔
Modern sequencing is rapid, OR comparatively inexpensive. ✔
Computer algorithms align corresponding DNA sequences. ✔
Similarities and differences between these sequences are identified. ✔
Fewer sequence differences generally indicate closer relatedness. ✔
Comparisons reveal common ancestry or estimate divergence timing using a calibrated molecular clock. ✔
The inferred relationships can be represented as an evolutionary tree. ✔
(c) Genes encode proteins, including enzymes. ✔
Phenotype comprises an organism’s observable traits. ✔
Genotype, alleles and gene expression influence those traits. ✔
A dominant allele can determine a trait in a heterozygote. ✔
A recessive autosomal trait is expressed when both copies are recessive. ✔
Incomplete dominance OR codominance provides another allele relationship. ✔
Many traits depend on multiple genes. ✔
Plasticity is the capacity to develop or change phenotypic traits. ✔
Environmental conditions can elicit these different traits. ✔
Changes in which genes are expressed can mediate the response. ✔
Epigenetic regulation affects phenotype or gene expression, OR epigenetic changes leave the DNA sequence unchanged, OR plasticity does not involve a change in the genome. ✔
Some plastic responses are reversible. ✔
Skin tanning in response to sunlight illustrates phenotypic plasticity. ✔
Schemat punktowania
(a) Award up to 4 distinct diagram points. A pentagon is required for sugar-position credit; that point can still earn credit without antiparallel orientation. Hydrogen-bond credit does not require the correct 2-versus-3 pairing count, following the source rubric. (b) Award any 4 points, maximum 4. (c) Award any 7 points, maximum 7; reversibility or a named example must explicitly concern plasticity. Quality: award 1 additional mark for a response across all parts that is readily understandable, concise and largely free of repetition or irrelevant material. Judge quality separately from content. Maximum 16 overall.