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Midterm

BIOL 1002 Study Guide - Midterm Guide: Microspore, Cotyledon, Endosperm

19 pages71 viewsWinter 2014

Department
Biological Sciences
Course Code
BIOL 1002
Professor
All
Study Guide
Midterm

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CHAPTER 44
GAMETOPHYTE DEVELOPMENT IN FLOWERING PLANTS
MALE:
The gametophytes are haploid and develop
within sporophyte flowers. They are very
small compared to the sporophyte and cannot
live on their own.
Pollen (male gametophyte) develops within
the pollen sacs of anthers.
1) Microspore mother cell (a.k.a.
microsporocyte) develops inside the pollen
sacs
2) Diploid microspore mother cells
divide by meiosis to form 4 haploid
microspores from each microspore
mother cell.
3) Each microspore divides by mitosis to
make an immature pollen grain containing:
a. tube cell.
b. generative cell (inside the tube cell)
4) The generative cell goes through
mitosis to form two sperm cells. This is now the mature pollen grain (see fig 44-5).
Once the pollen matures, the anther splits open and breezes carry away the pollen.
FEMALE:
Embryo sac development (see fig 44-7)
Within the ovary of a carpel, masses of cells differentiate into ovules. The outer layers of the
ovule are the integument.
The tissue of the ovule is diploid.
The series of events leading to the
female gametophyte are
1) The megaspore mother
cell (a.k.a. megasporocyte)
develops within the ovule that
is within the ovary of the
carpel.
2) The megaspore mother cell divides
by meiosis to form four haploid
megaspores.
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3) One of the four megaspores survives.
4) The remaining one of the four goes through 3 rounds of mitosis, producing eight
haploid nuclei. Plasma membranes and cells walls then form, dividing the cytoplasm
into the seven cells that make up the female gametophyte.
5) There are 3 small cells at each end (each with one nucleus), and one large central
cell with two nuclei. (The egg is one of the 3 cells at the lower end, located near an
opening in the integuments of the ovule.
The larger center cell becomes the primary endosperm cell.
POLLINATION AND FERTILIZATION (see fig 44-8)
1) Pollination starts when pollen leaves an anther and lands on a stigma. The pollen absorbs
water from the stigma.
2) The tube cell breaks through the pollen coat, and the pollen grain grows a tube down
through the style towards the ovary. It reaches the opening in the integuments of the ovule.
3) The pollen grain releases 2 sperm cells from the generative cell move down the tube to the
ovary where a double fertilization occurs.
Double Fertilization
- One sperm fuses with the egg cell to form the diploid zygote.
- The other sperm fuses with the polar nuclei in the primary endosperm cell making this
triploid endosperm (3 sets of chromosomes) tissue.
DEVELOPMENT OF SEEDS ANDS (see fig 44-9)
The seed develops from the ovule.
1) The integuments become the seed coat.
2) The primary endosperm divides. The daughter cells absorb nutrients from the parent
plant, forming a food-filled endosperm (acts as food for the new plant).
3) The zygote becomes the embryo.
The walls of the ovary turn into the flesh of the fruit.
As the seed grows, the embryo differentiates into shoots and roots. The shoot portion
includes one or two cotyledons (seed leaves) (see fig 44-10).
In dicots there are 2 cotyledons in the embryo, and monocots have only 1 cotyledon.
In the monocots, the cotyledon is protected by a tough sheath called the coleoptile (see fig
44-11).
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 Monocot Dicot 
COEVOLUTION OF FLOWERS AND POLLINATORS
Animal pollinated flowers have several modifications in order to:
- Attract animal pollinators
- Frustrate undesirable visitors
- Ensure cross-fertilization
Bee pollinated flowers:
- Brightly colored (white, yellow, or blue) with ultraviolet patterns. Bees cannot see red, and
they see near-UV, which is invisible to humans.
- These flower are tubular and produce their nectar (the food enticement) at the bottom of a
short tube, so the bee has to push past the stamens to get to it.
Butterfly pollinated flowers:
- Also brightly colored with have long tubular flowers.
Moth pollinated flowers:
- Light colored and sweet smelling so they’re easier to find in the dark.
- Typically night flowering plants.
Fly pollinated flowers (see case study page 865):
- Smell like rotting flesh or dung
Hummingbird pollinated flowers:
- Very deep tubular flowers of red or orange colors that produce large amounts of nectar.
- These flowers usually lack fragrance (birds attracted by color not scent) and don’t have a
landing zone.
Copulatory pollinated flowers:
- Sex is the enticement.
Some orchids mimic female wasps in scent and shape, attracting males that attempt to
copulate with the flower picking up pollen in the process.
The main function of the fruit is to aid in seed dispersal
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