Numerical answer
The four sentences below, numbered 1–4, can be arranged into a coherent paragraph. Decide on the correct order.
1. Coral polyps, in turn, expel the algae when stressed by unusually warm water, a process visible to us as coral bleaching.
2. Coral reefs owe their vivid colour to microscopic algae living within the tissue of coral polyps, in a relationship that benefits both partners.
3. A bleached reef is not necessarily a dead one — corals can recover their algae, and their colour, if water temperatures fall again before the coral itself starves.
4. The algae photosynthesise and share the resulting nutrients with their coral hosts, while the coral provides the algae shelter and compounds needed for photosynthesis.
Enter the correct order as a 4-digit number (e.g. 2413).
1. Coral polyps, in turn, expel the algae when stressed by unusually warm water, a process visible to us as coral bleaching.
2. Coral reefs owe their vivid colour to microscopic algae living within the tissue of coral polyps, in a relationship that benefits both partners.
3. A bleached reef is not necessarily a dead one — corals can recover their algae, and their colour, if water temperatures fall again before the coral itself starves.
4. The algae photosynthesise and share the resulting nutrients with their coral hosts, while the coral provides the algae shelter and compounds needed for photosynthesis.
Enter the correct order as a 4-digit number (e.g. 2413).
Show answer and solution
Answer: 2413
Sentence 2 introduces the coral-algae relationship generally ('a relationship that benefits both partners'), sentence 4 explains that mutual benefit specifically (photosynthesis/nutrients for shelter/compounds), sentence 1 introduces the disruption (bleaching under heat stress), and sentence 3 closes with the possibility of recovery after bleaching. The logical flow is: relationship → mechanism of benefit → disruption → possible recovery, giving order 2-4-1-3.
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