How do plant roots "know" to grow downward? this is a plant response called
a) gravitropism.
b) hydrotropism.
c) phototropism.
d) thigmotropism.

The correct answer would be A) gravitropism

Gravitropism or geotropism refers to the differential growth of a plant in response to the gravitational pull.

For example, roots show positive geotropism, that is, they grow in direction of gravitational pull.

In contrast, shoots show negative geotropism, that is, they grow in opposite direction as compared to the direction of gravitational pull.

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.

the match duh

explanation: