1. Explain what a megaspore and a microspore is, where they come from and what
they produce.
Megaspore-product of the megasporangia that develops into the female
gametophyte which produces large gametes called eggs.
Microspores-produce of the microsporangia that develops into the male
gametophyte which produces small gametes called sperm.
*A plant that produces these is heterosporous.
2. Explain the gymnosperm life cycle
A sporophyte (2n) produces cones called the microsporangia and the
megasporangia.
The microsporangia divides by meiosis to produce microspores (n) that
divide by mitosis to form pollen grains (n)
The megasporangia divides inside of a mother cell that divides by meiosis to
form a megaspore (n) that undergoes mitosis to from the female
gametophyte containing egg cells (n).
The pollen grains are delivered by wind or animals to the female
gametophyte and delivers its sperm to fertilize the egg.
This becomes the embryo (2n) that matures inside a seed.
The seed becomes dispersed and grows into a new sporophyte (2n). Repeat.
3. Explain the angiosperm life cycle
A sporophyte (2n) includes a flower with stamens and carpels.
The stamens contain the anthers where the microsporangia (n) develops by
meiosis.
The carpel contains the ovary (fruit) which contains the ovules, which
produce the megasporangia (n) by meiosis.
The pollen grains are delivered to the carpel, and the two pollen grains
undergo double fertilization in the ovule. One sperm fuses with the egg to
form the diploid zygote (2n). The second sperm fuses with 2 nuclei in the
female gametophyte to form a triploid nutritive tissue called endosperm
(3n).
The seeds are dispersed and grow into a new sporophyte (2n). Repeat.
4. Why does this video relate to the direct-pollination hypothesis?
http://www.youtube.com/watch?v=GV0oLYLgSJs
Terms:
Gynmosperm (life cycle)
Angiosperm (life cycle)
Heterosporous
Megaspores
Microspores
Pollen grains
Flower
Stamens
Anthers
Carpel
Ovary
Double fertilization
Endosperm
Directed pollination hypothesis
Pollination syndrome
Fruit
Monocotyledons (monocots)
Dicotyledons (dicots)
Cotyledons
Ginkgophyta
Cycadophyta
Pinophyta
Gnetophyta