Zadanie 7, Paper 2, maj 2026, TZ1, Biologia IB SL
Wzorowane na: Biology SL Paper 2, May 2026, TZ1, pytanie 7. Treść, dane i kontekst są zmienione; sprawdzane umiejętności, format i punktacja jak w oryginale.
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Zadanie
Polecenie
An unaffected couple has a child with phenylketonuria, an autosomal recessive disorder. Use P for the functional allele and p for the recessive allele. Other parts concern respiratory defence and gas exchange.
(a) Describe how the disorder can be inherited in this family.
(b) Outline how mucous membranes protect against pathogens.
(c) Explain how lung structure and inspiration promote respiratory gas exchange.
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Pokaż rozwiązanieUkryj rozwiązanieKlucz i punktacja
Odpowiedź z klucza
(a) Both parents must carry the recessive allele: Pp. ✔
Each parent has a one-half chance of passing on p (or P). ✔
Each child has a one-quarter chance of pp, OR three-quarters chance of being unaffected. ✔
The pp genotype expresses the disorder. ✔
A child has a one-half chance of being a heterozygous carrier. ✔
(b) Mucous membranes provide an initial barrier against pathogens. ✔
They secrete mucus. ✔
The sticky secretion traps pathogens. ✔
Trapped material can then be removed from the body. ✔
Cilia or coughing expel mucus from airways. ✔
Swallowed mucus carries pathogens towards stomach acid. ✔
Antimicrobial enzymes such as lysozyme can destroy pathogens. ✔
(c) Many alveoli provide a large diffusion area. ✔
Their thin walls shorten the diffusion path. ✔
The moist alveolar lining lets oxygen dissolve, while surfactant lowers surface tension and helps prevent collapse. ✔
A dense capillary network supports gas diffusion. ✔
Ventilation OR blood flow maintains concentration gradients. ✔
During inspiration the diaphragm contracts, OR flattens, OR moves downwards. ✔
External intercostal contraction lifts the ribs upwards and outwards. ✔
Thoracic volume rises. ✔
Pressure in the lungs falls below atmospheric pressure. ✔
Air flows into the lungs. ✔
Oxygen diffuses into blood while carbon dioxide diffuses towards alveolar air. ✔
Schemat punktowania
(a) Award any 4 points, maximum 4; accept a labelled Punnett grid. (b) Award any 4 points, maximum 4. (c) Award any 7 points, maximum 7. For the lining point accept oxygen dissolving in moisture OR surfactant reducing tension/preventing sticking, without requiring both. Do not credit internal intercostal contraction as the inspiratory action. Quality: award 1 additional mark when the whole response is clear on first reading, concise and substantially free of irrelevant repetition. Judge quality independently of content. Maximum 16 overall.