The two body forms of some radiates is an example of alternation of generations.

Question

Answer the following statement true (T) or false (F)

Answer 1

False

Clarify Question

• What is the key concept addressed by the question?
   o The question is asking you whether the polyp and medusa forms of cnidarians are examples of gametophyte and sporophyte forms of plants.
• What type of thinking is required?
   o The question requires you to apply what you know about the cnidarian forms to what you know about the plant forms.
• What key words does the question contain and what do they mean?
   o Radiates: animals of the phyla Cnidaria and Ctenophora, so named because they are radially symmetrical
   o Alternation of generations: the life cycle of plants, where a multicellular haploid form (gametophyte) alternates with a multicellular diploid form (spermatophyte)

Gather Content

• What are the two body forms of the Radiata?
   o The question is asking you about the Radiata, but you are expected to realize it is referring specifically to cnidarians. Many cnidarians alternate body forms with a sessile polyp budding off motile medusa. The medusae then reproduce sexually, forming a zygote that becomes a larva that eventually metamorphoses into a new polyp. This is an alternation of body forms, but is it "alternation of generations"?

• So what is alternation of generations?
   o Plants also follow a life cycle in which two forms alternate. One form (the spermatophyte) is multicellular and diploid. Spermatophyte undergo meiosis to form haploid spores, which then grow into multicellular haploid forms called gametophytes. The gametophytes produce haploid gametes by mitosis. Two gametes fuse together to form a zygote that develops into a new sporophyte.

Consider Possibilities

• What do the answer choices say?
   o This is a true/false item, so the options are limited. Both situations contain two different body forms, so what's different about them. Let's focus on the fact that one of the body forms in alternation of generations (the gametophyte) is haploid. Are either the medusa or the polyp haploid?

Choose Answer

• So which statement is true?
   o In the general animal life cycle, only the gametes are haploid. In cnidarians, medusa are diploid forms that make gametes by meiosis (not mitosis like gametophytes). The two body forms of the radiates are not an example of alternation of generations. The statement is false.

Reflect on Process

• Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
   o The question was asking you to compare dimorphism in cnidarians to alteration of generations.
   o To get the correct answer, you needed to a) understand which two forms cnidarians have and b) what alternation of generations is.
   o If you got the correct answer, congratulations. If not, did you identify the polyp and medusa as the forms you were being asked about?
   o Did you correctly recall the key features of alternation of generations?
   o Did you overlook that animals are diploid while gametophytes are haploid?