Life cycles of early land plants

Question 1

meiosis definition

Answer 1

diploid nucleus becomes haploid daughter cells

Question 2

define fertilisation/syngamy

Answer 2

haploid cells fuse to produce diploid nucleus

Question 3

define isogamy

Answer 3

two gametes that fuse are not differentiated in size so cannot identify male or female gametes (have - or + strains instead)

Question 4

define anisogamy

Answer 4

two gametes that fuse are differentiated in size and the female gamete is the largest one

Question 5

oogamy definition

Answer 5

extreme anisogamy where the female gamete has lost motility and is much larger than the male gamete. Egg and sperm

Question 6

how do the generations occur in plants?

Answer 6

haploid (gametophyte) and diploid (sporophyte) generations alternate (different to in animals which are zygote to zygote)

Question 7

what is the life cycle of the chlorophyte?

Answer 7

1. Diploid zygotę which is sometimes a resting stage
2. Zygote becomes a zygospore (resting zygote)
3. When zygospore is reactivated it undergoes meiosis to make daughter cells with + or - strain cells
4. Daughter cells grow and divide until they are large enough to undergo mitosis and make gametes
5. Motile gametes fuze and form zygotes

Question 8

what is the life cycle of a streptophyte?

Answer 8

• Diploid egg is retained on haploid parent
• Can form a zygospore
• Undergoes meiosis to make haploid spores
• Spores germinate and grow to make gametes

Question 9

life cycles with one haploid generation and one diploid generation

Answer 9

• Zygote, instead of immediately making daughter cells, grow into a multicellular embryo and then a sporophyte (diploid individual)
• Sporophyte makes haploid spores that grow into gametophytes that make gametes
• Very similar to algae (just evolved a sporophyte multicellular phase)

Question 10

why evolve a sporophyte?

Answer 10

• Spores are desiccation resistant and can be dispersed by wind
• Algae zygotes need a watery medium
• Sporophytes amplify the number of spores that can be produced from each zygote (algae only produce four spores from each zygote) - more chance of successful reproduction
• Sporophyte longevity, photosynthetic ability and size become more complex as vascular and seed plants evolve
• Gametophytes become less ecologically dominant

Question 11

why evolve sporophytic dominance?

Answer 11

Sporophytes amplify number of spores from each zygote and so sporophytic dominance amplifies that further - can live through multiple reproductive seasons and produce many spores

Question 12

Sporophytes amplify number of spores from each zygote and so sporophytic dominance amplifies that further - can live through multiple reproductive seasons and produce many spores

Answer 12

• Could land plants have evolved the same morphological diversity with ancestral algal life cycle?Could we have had giant moss gametophytes?
• A tree sized moss gametophytes would produce gametangia and the rain fall would disperse to archegonia (could have worked)
• This life cycle would have been dependent on external factor (rain availability) - this would have limited ability to colonise all biomes (dry areas especially)

Question 13

what organisms have one multicellular diploid generation? would this work for plants?

Answer 13

• animals
• brown algae called fucus

Fucus:
Zygote is diploid and grows into an embryo
Embryo grows into mature diploid individual
Produce sperm and eggs which are released into the water and fuse to produce zygote

• no, too dry on land