Zadanie 9, Paper 2, maj 2025, TZ1, Biologia IB HL
Wzorowane na: Biology HL Paper 2, May 2025, TZ1, pytanie 9. Treść, dane i kontekst są zmienione; sprawdzane umiejętności, format i punktacja jak w oryginale.
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Zadanie
Polecenie
A multicellular organism uses inherited DNA information during development and reproduction.
(a) Describe causes of base substitutions and their possible consequences.
(b) Distinguish between mitotic and meiotic cell division in eukaryotes.
(c) Explain how regulation of transcription can influence an organism’s phenotype.
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Odpowiedź z klucza
(a)
Replication errors or mutagen exposure can cause substitutions. ✔
A substitution randomly replaces one base with another and can alter a codon. ✔
Some substitutions are silent because of code degeneracy; some non-regulatory, non-coding changes also have no detectable effect. ✔
A changed codon may specify a different amino acid. ✔
A resulting change in sequence, folding or length can alter protein function; a new stop codon can shorten the product. ✔
Germline changes may pass to offspring; alternatively, some somatic changes contribute to cancer. ✔
A valid specific example illustrates a substitution and its effect. ✔
(b)
Mitosis preserves chromosome number, whereas meiosis halves it. ✔
Mitosis supports growth and repair, whereas meiosis forms haploid cells for sexual reproduction. ✔
Mitosis normally occurs in somatic lineages, whereas meiosis occurs in reproductive cell lineages. ✔
Mitosis involves one division, whereas meiosis involves two. ✔
Crossing over is characteristic of meiosis but not ordinary mitosis. ✔
Mitosis normally produces two cells, whereas meiosis normally produces four haploid products. ✔
Mitosis separates sister chromatids, whereas meiosis I separates homologues and meiosis II separates sisters. ✔
Mitotic products are normally genetically similar, whereas meiotic products differ genetically. ✔
(c)
Transcription factors can activate or repress transcription through DNA binding. ✔
A promoter provides the site for initiation by RNA polymerase; binding of regulatory proteins can promote initiation. ✔
Regulators at enhancers or silencers can raise or lower transcription rate. ✔
Epigenetic marks can change expression without changing the base sequence. ✔
Methylation of promoter cytosines can repress transcription. ✔
Histone modification can activate or repress expression depending on its position and type. ✔
Regulation changes production of proteins whose activities contribute to phenotype. ✔
Signals such as steroid hormones can activate receptors that regulate transcription. ✔
Environmental exposures can change epigenetic marks and expression. ✔
A valid specific example connects a transcriptional control mechanism to gene expression. ✔
Quality of communication: the complete response is understandable on first reading, focused and sufficiently concise, without substantial repetition or irrelevant material. ✔
Schemat punktowania
Part (a): award any 4 listed valid points, maximum 4 marks. Part (b): award any 4 listed valid points, maximum 4 marks. Part (c): award any 7 listed valid points, maximum 7 marks. Award 1 additional mark for clarity of communication across the whole response. Maximum 16 marks.