133 - ___ = ___ / 116 = 75.5

Bio 332
Fall 2001

Exam III

Name______________________

This is a take-home exam given before Thanksgiving break, it must be handed in on the Monday after Thanksgiving. All answers must be limited to the space provided on the PRINTED side of each page; answers continuing on the backs of pages or on attached pages will not be scored...brevity and concise answers are required. Late papers receive the late penalty listed on the syllabus. This exam covers eukaryotic algae, bryophytes, and lower-vascular plants (ferns and allies including Selaginella). In this coverage, the plant kingdom evolves toward an assemblage of vascularized seed-bearing plants. The questions on this exam should reflect your understanding of this evolutionary progression.

Common Threads. Assuming for a moment that these organisms constitute a clade, what are the synapomorphies among these plants? (8 points)
photosynthetic pigmentschlorophyll a,b
main storage carbohydratestarch
cell wall polysaccharidecellulose + pectin etc.
ribosomes80S cytoplasmic, 70S chloroplast and mitochondrion
DNA organizationhistone bound, linear, multiple chromosomes
nuclear envelopepresent except in mitosis
nuclear divisionmitosis
cytokinesisphragmoplast/cell plate

Evolution of life history. Among these groups there are three distinctly different life-histories: haplontic, diplontic, and diplohaplontic. Briefly describe each one. (6 points)
Haplonticdominant multicellular haploid
diploid is single cell
Diplonticdominant multicellular diploid
haploid is single cell
Diplohaplonticboth haploid and diploid are multicellular
Now write a short paragraph explaining what you believe is the plesiomorphic history and which is the most-apomorphic history among these groups. Defend your answer carefully and as thoroughly as possible in the space below. Consider the transition to terrestrial life in your answer. (5 points)
Zygotic (haplontic) is the plesiomorphic history. Monerans are haploid as the outgroup. Aquatic organisms of the ancient environment were shielded from UV mutagen so it was sufficient to be haploid through much of the life history. With the move to land, exposure to UV in the atmosphere gave higher mutation rates, so it was adaptive to shield lethal mutant alleles as recessives in heterozygous diploid genotypes. The elaboration of the diploid phase of the life history leads to greater genetic diversity for more-rapid colonization of diverse habitats and better ability to withstand a changing environment. The progression of adaptations to terrestrial life among these organisms correlates with transition to the sporic (diplohaplontic) life history among these organisms. This progression is probably leading ultimately to the gametic (diplontic) life history as the haploid is further reduced toward a single cell; it is not there yet in higher plants however.

Evolution of gametophytes. Trace the evolution through these organisms of the gametophyte from most primitive of the algae through those in Selaginella. While describing the gametophyte plant body in each group, be sure to indicate apomorphies that appear along this path of evolution both within and among the groups. (41 points divided as shown below)
ThallusGametangia
Green Algaeunicellular
colonial
filamentous
parenchymatous

(4 points)
female: isogametangium to oogonium
male: isogametangium to antheridium
cell wall is the only protective layer

(3 points)
Liverwortrhizoid
sheet-like thallus
PSN in chambers

(3 points)
female: archegonium
male: antheridium
both with sterile jacket of cells

(3 points)
Mossleafy shoot
rhizoid
vascular tissues (hydroid/leptoid)

(3 points)
female: archegonium
male: antheridium
sterile jacket

(3 points)
Psilotumheterotrophic
subterranean
fungal association
thallus + rhizoid as liverwort

(4 points)
female: archegonium
male: antheridium
sterile jacket

(3 points)
Fernthallus
rhizoid
autotrophic

(3 points)
female: archegonium
male: antheridium
sterile jacket

(3 points)
Selaginellamega: endosporic thallus
rhizoid
heterotrophic
stored reserves
micro: none, no thallus!

(5 points)
female: archegonium
sterile jacket
male: microspore wall is antheridium
no sterile jacket!

(4 points)

Evolution of gametes. Among these groups there are three distinctly different gamete conditions: isogametes, anisogametes, oogametes. Briefly describe each one. (6 points)
Isogametessame size
both motile
Anisogametesdifferent size
both motile
Oogameteslarge sessile egg
small motile sperm
Now write a short paragraph explaining what you believe is the plesiomorphic and which is the most-apomorphic gamete condition among these groups. Defend your answer carefully and as thoroughly as possible in the space below. Consider the transition to terrestrial life in your answer. (5 points)
Isogamous is plesiomorphic as conjugating monerans (the outgroup) have isomorphic cells. Motile gametes are needed in an aquatic environment where life originated to keep these photosynthetic organisms in the photic zone. Anisogamy is transitional to the apomorphic oogamy. Having sessile gametes avoids the need for water in the life history for the transition to terrestrial life. Having the sessile gamete attached to the sporophyte provides continuous nourishment from sporophyte to sporophyte as the gametophyte is reduced ultimately into a single cell.

Evolution of sporophytes. Repeat your tracing of the evolutionary pathway as you did for gametophytes, but now with respect to sporophyte and sporangia. (52 points divided as shown below)
Sporophyte BodySporangium
Green Algaesingle cell to thallus
(2 points)
cell wall only (no sterile jacket)
(zoosporangium)

(1 point)
Liverwortfoot
stalk
capsule
dependent on gametophyte
vascular (hydroid/leptoid)

(5 points)
sterile jacket
elaters

(2 points)
Anthocerosfoot
intercalary meristem
sporangium
photosynthetic
vascular (hydroid/leptoid)

(5 points)
sterile jacket
indeterminate

(2 points)
Psilotumrhizoid
stem
enation
true xylem and phloem
exarch
protostele

(7 points)
synangium sterile jacket
(1 point)
Lycopodiumroot
stem
microphyll/sporophyll
strobilus
plectostele
exarch

(6 points)
sterile jacket
(1 point)
Fernroot
rhizome
megaphyll
mesarch
siphonostele
amphiphloic

(6 points)
annulus
lip cell
stalk
aggregated into sori

(4 points)
Selaginellaroot
rhizophore
stem
microphyll

(4 points)
megasporangium
one sporocyte
not shed
microsporangium
many microsporocytes
shed with endosporic microgametophyte

(6 points)

Evolution of spores. Among these groups there are distinctly different spore (meiotic product) conditions. Briefly describe the progression from algae to Selaginella. Write a short paragraph explaining what you believe is the plesiomorphic and which is the most-apomorphic spore condition among these groups. Defend your answer carefully and as thoroughly as possible in the space below. Consider the transition to terrestrial life in your answer. (10 points)
The zoospore, a motile meiotic product, would be the plesiomorphic condition in aquatic algae. The cell wall was not invested with cutin or sporopollenin. With transition to land, the spore became immotile and its wall was cutinized or invested with sporopollenin in bryophytes and ferns; this avoided desiccation in the terrestrial environment. The spore became sexually dimorphic in size and color as heterospory evolved for some ferns and Selaginella, and gender expression was moved into the sporophyte. The spore hosted mitotic divisions resulting in endosporic gametophytes. Ultimately this happened inside the spore wall prior to dispersal so that the microspore became a pollen grain. The megaspore was held in the sporangium bringing on a requirement for pollination; a fundamentally terrestrial process. This permits the gametophyte generation to be completely hosted by the sporophyte in terrestrial plants. Syngamy is hosted within the spore wall in these organisms so that ultimately (in gymnosperms) free water is no longer necessary for syngamy.



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