Zadanie 7, Paper 2, maj 2026, TZ2, Biologia IB SL
Wzorowane na: Biology SL Paper 2, May 2026, TZ2, pytanie 7. Treść, dane i kontekst są zmienione; sprawdzane umiejętności, format i punktacja jak w oryginale.
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Zadanie
Polecenie
A membrane’s molecular organization underlies selective transport and electrical properties.
(a) Outline phospholipid structure and its interactions with water.
(b) Explain how proteins enable substances to cross membranes.
(c) Describe the establishment of a neuronal resting potential.
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Odpowiedź z klucza
(a) A phospholipid has two fatty-acid tails. ✔
Its head contains phosphate linked to glycerol. ✔
It is amphipathic, OR explicitly has both hydrophilic and hydrophobic regions. ✔
The head is hydrophilic. ✔
The tails are hydrophobic. ✔
In water these molecules assemble into bilayers. ✔
(b) Integral proteins are embedded in the bilayer. ✔
Transmembrane proteins carry specified solutes or ions across it. ✔
Their specificity makes the membrane selectively permeable. ✔
Channels enable facilitated diffusion. ✔
Net passive flux follows the concentration gradient. ✔
Gated channels can open or close. ✔
Pumps perform active transport. ✔
ATP hydrolysis supplies energy for pumping. ✔
Active transport can move a solute against its gradient. ✔
Aquaporins facilitate rapid water movement. ✔
(c) The resting potential is approximately −70 mV. ✔
An active process establishes/maintains it, OR ATP is required. ✔
Sodium–potassium pumps control the process, OR the pump is identified as a transmembrane antiporter. ✔
Each pump cycle exports three sodium ions and imports two potassium ions. ✔
This establishes ion/electrochemical gradients. ✔
The cell interior is negative relative to the exterior. ✔
Schemat punktowania
(a) Award any 4 points, maximum 4. Require both phosphate and glycerol for the head-composition point; amphipathic OR the explicit presence of both hydrophilic and hydrophobic regions earns the general-property point; do not infer it merely from separate head/tail points. Accept an annotated drawing. (b) Award any 7 points, maximum 7. Qualify membrane/transmembrane proteins for the transport point; connect selectivity to proteins. (c) Award any 4 points, maximum 4; a correctly charge-labelled drawing may earn the polarity point. Award 1 additional quality mark for a clear, concise overall response with little irrelevant repetition; judge it independently of content. Maximum 16 overall.