Rigid skeletons are formed from materials including chitin (in arthropods), calcium compounds such as calcium carbonate (in stony corals and mollusks) and silicate (for diatoms and radiolarians).
D. Polar regions receive less solar energy and heat per unit area than tropical regions
Less direct sunlight means that there is less concentration of direct solar rays. This would influence temperature and would ultimately create weather, and since this pattern continues of switching direct ray latitudes, this would create climate zones all over the Earth, and similar ones with similar latitude and terrain.
Seasonal variations of climate impact the state of an ecosystem. In areas that experience a cold season, some elements of the ecosystem change their residence or even hibernate to survive. Succession can be considered a higher state of development of the ecosystem.
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