Zadanie 10, Paper 2, maj 2026, TZ3, Biologia IB HL
Wzorowane na: Biology HL Paper 2, May 2026, TZ3, pytanie 10. Treść, dane i kontekst są zmienione; sprawdzane umiejętności, format i punktacja jak w oryginale.
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Zadanie
Polecenie
Chemical messages coordinate cells and whole organisms.
(a) Describe bacterial quorum sensing.
(b) Outline roles of calcium ions in animal-cell signalling.
(c) Explain how plant hormones regulate growth through signalling.
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Odpowiedź z klucza
(a) Bacterial cells release diffusible signalling molecules. ✔
Their concentration rises as the population becomes denser. ✔
The molecules bind appropriate receptors. ✔
Above a threshold, receptor activation changes gene expression. ✔
At low density the signal disperses before it accumulates sufficiently. ✔
For example, quorum regulation can switch on bacterial light-producing enzymes in Vibrio fischeri; accept another correct example, such as quorum-regulated biofilm formation. ✔
(b) Calcium acts as a signal during synaptic transmission. ✔
Presynaptic depolarization triggers calcium entry, OR excitation of muscle triggers calcium release from the sarcoplasmic reticulum. ✔
Calcium moves through ion-channel proteins. ✔
It causes transmitter vesicles to approach or fuse with the presynaptic membrane. ✔
This leads to transmitter release into the cleft. ✔
Active transport subsequently removes cytosolic calcium from the terminal. ✔
Calcium also regulates muscle contraction. ✔
Calcium changes the conformation or position of muscle regulatory proteins, OR exposes myosin-binding sites on actin. Naming calcium binding to troponin is optional. ✔
(c) Plant hormones are produced by cells and transported to sites of action. ✔
Auxin promotes cell elongation or shoot growth. ✔
It promotes proton export into the cell-wall space. ✔
Wall acidification loosens connections within the cellulose network. ✔
Efflux carriers move auxin out of cells. ✔
Polar export and entry into adjacent cells establish directional auxin movement. ✔
Auxin gradients cause differential growth and bending. ✔
Shoot tips produce auxin, while root tips produce cytokinin. ✔
Auxin and cytokinin interact to balance root and shoot development. ✔
Cytokinin promotes cell division. ✔
Auxin suppresses axillary buds, OR cytokinin promotes their growth. ✔
Gibberellins can promote germination or stem growth. ✔
Abscisic acid can inhibit germination or shoot growth. ✔
Schemat punktowania
(a) Award any 4 points, maximum 4. Release must be explicit for the signal point; in a bioluminescence example, the bacteria themselves produce light. Other correct quorum-sensing examples are accepted. (b) Award any 4 points, maximum 4. Nerve-impulse propagation alone is not the synaptic-transmission point. (c) Award any 7 points, maximum 7. Ethylene/ripening alone is outside this growth question. Penalize confusion of cytokinin with cytokine only once. Quality: award 1 additional mark for a response across all parts that is readily understandable, concise and largely free of repetition or irrelevant material. Judge quality separately from content. Maximum 16 overall.