Lecture 21: Alternation of generation Flashcards
Sporophyte
plant that produces spores
What is the ploidy of the sporophyte phaseof the plants life cycle?
Diploid (2n)
What is meiosis?
Cell division where 1 diploid cell (2n) divides to form 4 haploid cells (n)
What is a spore?
The product of meiosis…. haploid cells resulting from meiotic cell division
What does the spore mark?
The initiation of the gametophyte generation
What is a gametophyte?
A plant that produces gametes (like egg and sperm)
What is the ploidy of the gametophyte phase of a plant’s life cycle??
haploid (n)
What is a gamete?
Egg and sperm….produced from the mitotic cell divisions of the gametophyte
What happen to the 2 gametes at fertilization?
egg and sperm fuse to produce a zygote
What is a zygote?
The product of egg and sperm fusion
What ploidy is a zygote?
A diploid because it results from the fusion of 2 haploid gametes
What marks the initiation of the sporophyte generation?
the zygote
Alternation of generations (between sporophyte and gametophyte stages) can vary among plants for (3 things)
- physical appearance of each stage (size, form, vigor)
- time spent in each stage (is it persistent? emphemeral ?)
- mechanics of gamete production and fusion (are there many or few cell divisions? How do the gametes find each other?)
What ploidy is moss in the gameteophyte stage?
haploid (n)
What is a bryophyte? Give an example.
A non-flowering plant (moss and fern)
What is the haploid gametophyte in moss?
The green bit!
What does the sporophyte form on moss?
a sporangium (capsule) in which cell divide meiotically and form spores
What is the relationship between the sporophyte and the gametophyte in moss?
Sporophyte grows on, is supported by and gain nutrition from gametophyte
What does the sporophyte generation look like in a fern?
What we regularly think of as a fern
What are sori?
Sporangia in fern (formed on the underside of fronds)
Characteristics of sori
conspicuous, hardy, long-lived
What is a prothallus?
heart-shaped structure where antheridia and archegonia form on surface
What do gametes form inside through mitotic divisions?
Antheridia
Characteristics of prothallus
inconspicuous, fragile, short lived
What happens during pollen formation in flowering plants?
Haploid spore divides by mitosis so within each pollen grain there are 2 cells
What are the 2 cells in a pollen grain?
1 tube cell and 1 generative cell
What does pollen consist of?
4 haploid cells formed with a spore with a protective coat (exine coat)
Why do flowering plants need 2 sperm cells?
So 1 can fertilize the egg to form a zygote while 1 gets with 2 female nuclei to produce endosperm
What happens to a male gametophyte in angiosperms? (flowering plants)
It is reduced to just 3 cells held within a pollen grain (1 tube cell and 2 sperm) are dispersed via wind and pollinators
What happens to the microspore mother cells in an anter?
They divide by meiosis to form 4 haploid cells
What happens to the megaspore mother cell?
Divides by meiosis in megasporangium (located in ovule)
How many of the cells survive after the megaspore mother cell divides by meiosis?
1/4
How many mitotic divisions does the megaspore mother cell undergo? How many cells does it yield?
3…..8 cells arrange in an embryo sac to prepare for fertilization (**female gameteophyte is reduced to 8 cells at this point)
What forms the embryo of the seed?
A fusion of the egg and sperm makes the zygote
Dispersal agent of moss
water
dispersal agent of fern
water
Dispersal agent of angiosperm
wind and pollinators
What is the male gameteophyte type in moss?
Flagellated
What is the male gameteophyte type in ferns?
flagellated
What is the male gameteophyte type in angiosperm
non-flagella
Dominant generation in moss
gameteophyte
Dominant generation in ferns
sporophyte
Dominant generation in angiosperms
sporophyte
