Which of the following is a component of healthy soil ecosystems? a. fungi b. bacteria c. nematodes d. all of the above

d. all of the above

The soil microbes and insects plays an important role in maintaining the fertility of the soil. Also, the soil is the habitat of large diversity of these insects  and microbes. The fungi, bacteria and insects- nematodes decomposes the plant litter in the form of leaves, twigs and other organic matter available in the soil and helps in preparation of humus in the soil. Humus is a dark colored, sticky substance which is rich in organic matter and supports the growth of the plants. The healthier the soil, the more plants will grow and more litter will produce which otherwise favor the soil ecosystem.  

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organisms that lack symmetry are called asymmetrical and belong to phylum porifera/sponges.

organisms with specialized stinging cells belong to phylum cnidaria. stinging cells are called cnidoblast cells.

cnidarians show two morphological forms : polyp (sessile) and medusa (mobile)

filter feeding is observed in porifera members.  

alternation of generation is observed in coelenterata or cnidaria. there is alternation of asexual polyp form and sexual medusoid form. it is also referred as metagenesis.