2. Two Types of Substances. Some substances are made of only one kind of atom. Other
substances are made of more than one kind of atom. How are the properties of these two
types of substances different?

Elements and compounds

Explanation:

Substances are purely classified as pure and impure substances.

Pure substances are those with a definite composition which are simply elements and compounds.

Impure substances are those with an indefinite composition which are mixtures.

How are their properties different;

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explanation:

jujj

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.