Zadanie 6, Paper 2, maj 2022, TZ2, Biologia IB SL
Wzorowane na: Biology SL Paper 2, May 2022, TZ2, pytanie 6. Treść, dane i kontekst są zmienione; sprawdzane umiejętności, format i punktacja jak w oryginale.
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Zadanie
Polecenie
Haemophilia can result from inadequate activity of a blood-clotting protein.
(a) Outline how translation produces a polypeptide in a cell.
(b) A woman carrying the usual X-linked recessive haemophilia allele has children with a man without that allele. Determine the probabilities for their children, showing your working.
(c) Explain blood clotting and the consequences of a clotting-factor deficiency.
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Odpowiedź z klucza
(a) Translation occurs at ribosomes. ✔
The mRNA sequence specifies the amino-acid sequence. ✔
The mRNA sequence derives from the DNA sequence of a gene. ✔
A three-base codon specifies an amino acid. ✔
Codons are on mRNA and anticodons on tRNA. ✔
mRNA binds a ribosome. ✔
tRNA brings amino acids to the ribosome. ✔
A start codon initiates translation OR a stop codon terminates it. ✔
The ribosome progresses along successive codons to extend the chain. ✔
Peptide bonds link amino acids. ✔
Complementary codon–anticodon pairing helps determine amino-acid order. ✔
(b) Let Xᴴ be the unaffected allele and Xʰ the recessive haemophilia allele. Parents: XᴴXʰ and XᴴY. ✔
The four equally likely combinations are XᴴXᴴ, XᴴXʰ, XᴴY and XʰY. ✔
Half the sons are expected to have haemophilia; no daughters are expected to have it, and half the daughters are carriers. Across all children, assuming equal sex probability, 25% are expected to be affected. ✔
(c) Clotting seals damage in skin or vessels. ✔
Platelets release clotting factors. ✔
Thrombin is activated. ✔
A cascade of reactions amplifies the response. ✔
Thrombin converts fibrinogen to fibrin. ✔
Fibrin forms a clot OR blocks the damaged region OR prevents blood loss. ✔
Insufficient clotting-factor activity delays or impairs stable clot formation. ✔
An incompletely sealed wound can allow pathogen entry. ✔
Prolonged bleeding can reduce blood volume or pressure and can be life-threatening. ✔
Blood loss reduces haemoglobin OR oxygen-carrying capacity. ✔
Bleeding risk affects activities or procedures such as surgery, contact sport or childbirth. ✔
Quality: the response is clear on first reading, concise and contains little repetition or irrelevant material. ✔
Schemat punktowania
Part (a):any 5,maximum 5. Part (b):1 for labelled parental alleles,1 for all 4 offspring genotypes,1 for half of sons affected together with either no daughters affected OR half of daughters carriers; do not require both statements about daughters,maximum 3. Sex may be clear from the cross. Part (c):any 7,maximum 7. Award 1 independent quality mark. Total 16.