What is population density? answers are a. the number of organisms of a species
in a particular area. and b. the area occupied by a particular species in the ecosystem. c. the total number of organisms within a fixed area. and d. the total number of organisms of a particular species.

Option C.

Population density is the total number of organisms within a fixed area.

Explanation:

Population density is the total number of organisms per unit area. Population density is calculated by dividing the number of organisms by the unit area either in square kilometers, squaremeters, square miles.

Population density =number of organisms ÷ unit of land area.

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.