Quiz Two – Take Home (due Tuesday 10/24/06)

1. Several organisms we have studied have motile spores at some stage in their life cycle. Motile spores have been called swarm cells, zoospores and planogametes.

a. Define each term (1.5 points each) and write after each definition, all the phyla which have that type of spore (0.5 points for each correct phylum, -0.5 points for an incorrect phylum). For example if the Ascomycota has both zoospores and planogametes list Ascomycota under both headings.

i. Swarm cells:

flagellate cells of the Myxomycota and Plasmodiophoromycota that are anisokont with two anterior whiplash flagella. They form when excess water is available when spores germinate.

(acceptable: 1-4 whiplash flagella, anteriorly attached.)

ii. Zoospores:

motile, asexually produced spores found in the Oomycota, Hyphochytriomycota, Chytridiomycota, (Labyrinthulomycota and Plasmodiophoromycota.)

iii. Planogametes:

motile gametes, found in the Chytridiomycota (and Plasmodiophoromycota)

b. For any type of motile spore (i, ii, or iii, above) that is found in more than one phylum, draw the characteristic motile spore of each phylum including details on type and number of flagella, and swimming direction. (1 point for each correct diagram)

ii.

Chytridiomycota Hyphochytriomycota Oomycota

2a. Describe why the Oomycota are said to have a short haploid stage and a short dikaryon stage in their life cycle. In order to do this fully, you will need to explain where plasmogamy, karyogamy and meiosis take place in the life cycle. You can supplement your explanation with drawings. (5 points).

The Oomycota are said to have a short haploid stage and short dikaryotic stage because those stages are limited to single cells with no division of the nuclei. Meiosis takes place by the nuclei in the gametangia (oogonium, antheridium), after they develop, to produce the haploid nuclei. They are restricted to the gametes, the oospheres and antheridial nuclei. After formation, plasmogamy occurs via contact and an antheridial nucleus is transferred into the oosphere to produce a dikaryotic cell. Nuclear fusion then takes place to produce the diploid nucleus and begin development of the oospore. The oospore upon germination produces the diploid hyphae that initiate the asexual phase.

2b. Does mitosis of the haploid and/or dikaryon stage nuclei in the Oomcyota occur?

Explain your answer. (2 points)

No, there is no mitosis of the haploid or dikaryotic nuclei in the Oomycota There is an immediate progression following meiosis to plasmogamy and karyogamy with no mitotic nuclear division taking place. Mitosis doesn’t occur again until germination of the oospore.

2c. From which cell(s) does the asexual stage grow? Explain. (1 point)

The asexual stage grows from the oospores or from (encysted) zoospores.

3. Consider the life cycle of Allomyces macrogynus.:

a. What are the similarities and what are the differences between the cells labeled “K” and “J”? (2 points)

J and K are both zoospores. J zoospores are diploid, produced from mitosporangia (zoosporangia) of the sporothallus and K are haploid zoospores, produced in the meiosporangia (resistant sporangia) of the sporothallus.

3b. What are the similarities and what are the differences between the cells labeled “C” and “D”? (2 points)

C and D are both motile gametes, C is the male gamete and D is the female gamete. They differ in size (big female) and pigment, the male is orange.

3c. What are the structures labeled A and I and why are they given these names? What is the nuclear ploidy of these structures? (3 points)

A is the gametothallus and I is the sporothallus. They are named based on the types of spores they produce with the gametothallus producing planogametes and the sporothallus producing zoospores.

The gametothallus is haploid and the sporothallus is diploid.

3d. This lifecycle is said to be an example of a diplobiontic lifecycle. What does this mean and how does it apply to this lifecycle? (2 points).

A diplobiontic lifecycle is one where the haploid and diploid generations (phases) of the lifecycle are separate independent phases. It applies to Allomyces macrogynus because the gametothallus represents the growing haploid phase and the sporothallus the growing diploid phase.

[It is also referred to as alternation of generations]

3e. In this lifecycle, anisogamy takes place. What is anisogamy and where in the lifecycle does it occur (2 points)? How does this event tell you what phylum this lifecycle represents (2 points)?

Anisogamy is fusion between two morphologically different planogametes. It occurs between the planogametes ‘C’ and ‘D” which are the male and female gametes respectively. It tells you you are dealing with the Chytridiomycota because that is the phylum in which fusion of motile gametes takes place