In the early days of germ theory, contagious diseases were thought to be caused by fungi or bacteria. in the 1890s, dmitri
ivanovski filtered extracts from diseased tobacco plants and discovered that the disease could be transmitted to new plants
through the filtrate. he concluded that the disease was caused by particles smaller than bacteria: the tobacco mosaic virus.
which best explains how ivanovski's work led to a change in the germ theory?
he tried to promote his hypothesis as a law.
he used a new experimental method to test his hypothesis.
he used a more powerful bacterial strain than other scientists had.
he obtained results that confirmed what other scientists were thinking

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.

it is a

explanation:

the real answer is b. scintillation counter

both male and female gametes are produced by meiosis of the germ cells. therefore, both male and female gametes are haploid. one male and one female gamete unite during the fertilization to form the diploid zygote. in seed bearing plants, pollen grain is the male gametophyte, which produces sperm cells.