Zadanie 10, Paper 2, maj 2025, TZ2, Biologia IB HL
Wzorowane na: Biology HL Paper 2, May 2025, TZ2, pytanie 10. Treść, dane i kontekst są zmienione; sprawdzane umiejętności, format i punktacja jak w oryginale.
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Zadanie
Polecenie
Biological functions depend on molecular organization and coordination between body systems.
(a) Describe how codons determine polypeptide structure.
(b) Outline how photosystem structure supports its function.
(c) Explain how blood pH can fall during activity and how this changes ventilation in humans.
One additional mark is available for clear, concise communication across the whole response.
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Odpowiedź z klucza
(a) An mRNA codon consists of three bases. ✔
Each sense codon specifies one amino acid. ✔
AUG commonly starts translation and specifies methionine. ✔
UAA, UAG and UGA are termination signals. ✔
A tRNA anticodon pairs complementarily with an mRNA codon. ✔
The code is degenerate, with several codons able to specify the same amino acid. ✔
Codon order determines the amino-acid order, or primary structure, of the polypeptide. ✔
(b) Photosystems are embedded in thylakoid membranes. ✔
Photosynthetic electron transfer involves photosystem II and photosystem I. ✔
The pigment arrangement captures light energy. ✔
Energy reaches a reaction centre, permitting transfer of an excited electron to an acceptor. ✔
An array contains chlorophylls together with accessory pigments. ✔
Different pigments broaden the wavelengths of light that can be used. ✔
(c) Increased cellular respiration can raise carbon dioxide production and its concentration in blood. ✔
Exercise increases metabolic demand; during intense activity oxygen supply can become limiting. ✔
Dissolved carbon dioxide reacts with water, generating carbonic acid and hydrogen ions, lowering pH. ✔
Carbonic anhydrase accelerates this carbon dioxide hydration reaction. ✔
Chemoreceptors respond to increased carbon dioxide or hydrogen-ion concentration. ✔
Peripheral chemoreceptors occur in carotid and aortic bodies. ✔
Sensory information reaches respiratory control centres in the medulla. ✔
Motor signals adjust contraction of external intercostal muscles. ✔
Motor signals also adjust diaphragm contraction. ✔
These signals travel via intercostal and phrenic nerves. ✔
Ventilation frequency increases. ✔
Greater inspiratory muscle activity increases tidal volume, helping remove more carbon dioxide. ✔
Communication: the explanation is coherent, succinct and free of distracting repetition. ✔
Schemat punktowania
(a) Any 4, max 4. (b) Any 3, max 3. (c) Any 8 distinct points, max 8. Accept a scientifically accurate account of exercise-associated metabolic acidosis; do not require the inaccurate assertion that lactate production itself releases hydrogen ions. Add 1 holistic clarity mark across all parts, maximum 16. In (a), AUG initiation OR AUG coding for methionine suffices; stating there are three stop codons earns the stop point without requiring their names. In (b), emission/transfer of an excited electron suffices without naming an acceptor. In (c), exercise OR oxygen limitation suffices for the activity context; CO2 causing lower pH OR describing carbonic-acid/H+ formation suffices for the acidification point; naming intercostal OR phrenic nerve suffices for the nerve point.