Zadanie 7, Paper 2, maj 2026, TZ2, Biologia IB HL
Wzorowane na: Biology HL Paper 2, May 2026, TZ2, pytanie 7. Treść, dane i kontekst są zmienione; sprawdzane umiejętności, format i punktacja jak w oryginale.
Darmowe konto pozwoli wrócić do niego później.
Zadanie
Polecenie
Directional processes depend on structures that constrain movement.
(a) Outline how structures in the human circulatory system limit backward blood flow.
(b) Explain why transmission across a chemical synapse proceeds from the presynaptic to the postsynaptic neuron.
(c) Describe how DNA strand direction affects the way replication proceeds.
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Pokaż rozwiązanieUkryj rozwiązanieKlucz i punktacja
Odpowiedź z klucza
(a) Valves permit forward flow and close against backward flow. ✔
A reversal of the pressure difference closes a valve. ✔
Veins contain valves. ✔
Atrioventricular valves separate atria from ventricles. ✔
Semilunar valves occur at the ventricular exits. ✔
(b) The two sides differ structurally, with release machinery on the presynaptic side and reception on the postsynaptic side. ✔
An action potential arrives at the presynaptic terminal. ✔
The presynaptic membrane has voltage-gated calcium channels, OR those channels open. ✔
Calcium ions enter the terminal. ✔
Neurotransmitter vesicles move towards OR fuse with the presynaptic membrane. ✔
Neurotransmitter is released into the cleft. ✔
Release occurs by exocytosis. ✔
The transmitter diffuses across the cleft. ✔
The postsynaptic membrane has transmitter receptors, OR transmitter binds those receptors. ✔
Receptor activation opens ion channels, often allowing sodium entry at an excitatory synapse. ✔
A postsynaptic potential is produced; if threshold is reached, this can initiate an action potential. ✔
Transmitter is subsequently removed, broken down or taken up again. ✔
(c) Each strand has a 5′ end and a 3′ end. ✔
The 5′ end bears phosphate, OR the 3′ end terminates at deoxyribose. ✔
The two template strands are antiparallel. ✔
Helicase separates the helix into templates. ✔
Polymerase extends new DNA only in the 5′ to 3′ direction. ✔
The leading strand is synthesized continuously, OR synthesis proceeds towards the advancing fork. ✔
The lagging strand is synthesized discontinuously, OR synthesis proceeds away from the fork. ✔
It is produced as Okazaki fragments. ✔
Ligase seals these fragments into a continuous strand. ✔
Schemat punktowania
(a) Award any 3 listed points, maximum 3. (b) Award any 7, maximum 7. (c) Award any 5, maximum 5. Accept appropriately annotated diagrams. Quality: award 1 additional mark for an overall response across all parts that is readily understandable, concise and largely free of repetition and irrelevant material. Assess this separately from content. Maximum 16 marks overall.