Numerical answer
The four sentences below, when properly sequenced, form a coherent paragraph. Enter the correct order as a four-digit number (e.g. 3142).
1. Coral reefs, though they occupy less than one percent of the ocean floor, support an estimated quarter of all known marine species, making them among the most biologically dense ecosystems on the planet.
2. This density depends on a fragile symbiosis: the coral animal hosts microscopic algae that photosynthesise and supply it with food, a partnership that collapses when water temperatures rise even slightly above normal.
3. When the algae are expelled in this stress response, known as bleaching, the coral loses both its colour and its primary food source, and can starve within weeks if warm conditions persist.
4. Repeated bleaching events, now occurring with increasing frequency as ocean temperatures climb, leave reefs less time to recover between episodes, threatening the very biodiversity their density once seemed to guarantee.
1. Coral reefs, though they occupy less than one percent of the ocean floor, support an estimated quarter of all known marine species, making them among the most biologically dense ecosystems on the planet.
2. This density depends on a fragile symbiosis: the coral animal hosts microscopic algae that photosynthesise and supply it with food, a partnership that collapses when water temperatures rise even slightly above normal.
3. When the algae are expelled in this stress response, known as bleaching, the coral loses both its colour and its primary food source, and can starve within weeks if warm conditions persist.
4. Repeated bleaching events, now occurring with increasing frequency as ocean temperatures climb, leave reefs less time to recover between episodes, threatening the very biodiversity their density once seemed to guarantee.
Show answer and solution
Answer: 1234
Sentence 1 introduces coral reefs and their biodiversity, the natural opening. Sentence 2 explains the symbiotic mechanism underlying that density and flags its fragility, following logically from 1. Sentence 3 describes what happens when the symbiosis breaks down (bleaching), a direct continuation of 2. Sentence 4 discusses the cumulative, worsening effect of repeated such events, the natural closing point. Order: 1-2-3-4.
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