<span>Only about 75% of water is fresh and suitable for human use.
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Ecosystems maintain themselves by cycling energy and nutrients obtained from external sources. At the first trophic level<span>, </span>primary producers<span> (plants, algae, and some bacteria) use solar energy to produce organic plant material through photosynthesis. Herbivores—animals that feed solely on plants—make up the second trophic level. Predators that eat herbivores comprise the third trophic level; if larger predators are present, they represent still higher trophic levels. Organisms that feed at several trophic levels (for example, grizzly bears that eat berries and salmon) are classified at the highest of the trophic levels at which they feed. Decomposers, which include bacteria, fungi, molds, worms, and insects, break down wastes and dead organisms and return nutrients to the soil
I got this passage from Annenberg Learner
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The correct answer is option a, that is, multicellular, heterotrophic, and diploid.
Animals refer to the multicellular eukaryotic species, which forms the biological kingdom Animalia. Animals exhibit many features, which distinguish them from other living species. The animals are multicellular and eukaryotic, unlike prokaryotic bacteria, and unlike protists that are eukaryotic but unicellular.
The animals are heterotrophic, not like algae and plants that generate their own food. Almost all the animals make use of some kind of sexual reproduction. They are diploid and generate haploid gametes by the process of meiosis, the larger non-motile gametes are ova and the smaller motile gametes are spermatozoa.
