Download The megasporocyte divides by meiosis to produce the haploid

Chapter 23b-Angiosperms
Double Fertilization
The ovule is the site of meiosis and ultimately the formation of the
seed.
The ovule develops one or more layers of sterile tissue,
the integuments along with a megasporocyte, which is
embedded in the nucellus.
The megasporocyte divides by meiosis to produce the
haploid megaspores.
Of the four megaspores, generally only one remains.
Within the embryo sac, cell walls develop around some
of the nuclei, forming the egg and 2 other cells, the
synergids.
Other nuclei are not enclosed in cell walls. Some of these, the polar
nuclei, are located in the central region of the embryo sac.
This shows the mature ovule with the embryo sac
fully developed. Note that the egg and synergids
are located at the micropylar end and that the polar
nuclei are not far from the same end.
The pollen tube grows through the micropyle and the 2
sperm nuclei are released.
The phenomenon of two sperm nuclei combining with
different nuclei from the female gametophyte is termed
double fertilization, a phenomenon nearly unique to
angiosperms.
Flowers Vary in their Architecture
A flower with all four parts is a complete flower.
If it lacks one or more parts, it is an incomplete flower.
If a flower has both androecium and gynoecium (male
and female) it is called a perfect flower.
If only one sex is present, it is an imperfect flower.
Symmetry is also used to characterize flowers
Regular symmetry is when all the flower parts
Sedum
Irregular symmetry is when the flower parts are not equal.
Pisum
Flower parts may be free or united (fused).
In Sedum, the petals, sepals, stamens, and pistils are
completely separate and free.
In Narcissus, the petals are fused over part of their length
to form a tube.
Sedum
Ovary position also varies.
In some plants, the ovaries are clearly situated above the point of attachment of the other flower parts.
In other plants, the ovaries appear to be placed below the point of attachment of the other flower parts.
Superior ovary in Tulipa.
Inferior ovary in Narcissus.
A cluster of flowers is called an inflorescence
Angiosperms-Fruits
Fruits are derived from the ovary of the flower.
Fruits protect seeds, aid in seed dispersal, and
can be a factor in seed germination.
Fruit structure is highly constant for the same species in
different environments and therefore fruits are used in
classification.
Fruits are of three types:
Simple fruits are derived from a single ovary, the ovary
may have one or more carpels.
Aggregate fruits are derived from many separate ovaries
of a single flower, all attached to a common receptacle.
Carpels
Stamen
Raspberry flower
Carpel
(fruitlet)
Stigma
Ovary
Stamen
Raspberry fruit
Aggregate fruit
Multiple fruits are the enlarged ovaries of multiple flowers
that more or less fuse together.
Flower
Pineapple inflorescence
Each
segment
develops
from the
carpel
of one
flower
Pineapple fruit
Multiple fruit
A simple fruit – the almond
The almond has only a single carpel with one ovule.
A simple fruit – the legume, found in
peas, beans, etc.
Legumes have a single ovary and carpel, but there
are multiple ovules.
Fruits may be dehiscent (splits open) or indehiscent.
Additional simple, dehiscent fruits:
Follicle (Ex: Magnolia)
The follicle develops from a single carpel and opens
along only 1 side.
Capsule (Poppy)
Capsules are simple fruits derived from compound ovaries
Simple fruits can also be indehiscent, either dry or fleshy.
Nuts are one type of dry, indehiscent fruit.
Other dry, indehiscent simple fruits include: achene
The sunflower “seed” is actually an achene; the shell is
the pericarp.
Other dry, indehiscent simple fruits include: caryopsis
The “seeds” of corn and other grasses. The caryopsis
differs from the achene in that the pericarp is firmly
attached to the seed.
Other dry, indehiscent simple fruits include: samara
The winged fruits of maples and elms.
The wings are outgrowths from the ovary wall.
One of the most common fleshy simple fruits is the drupe.
Plants that produce drupes include
The almond is also a drupe, but we don’t see the
fleshy part. The initial fleshy pericarp eventually dries
and becomes the hard covering of the seed.
Other fleshy, simple fruits include:
Berry
Berries are derived from a compound ovary, and many
seeds are embedded in the fleshy pericarp.
The tomato is a berry.
Other fleshy, simple fruits include:
Pepo
The cucurbits (watermelon, cucumber, squash) are
pepos.
Pepos are specialized berries except with a rind that is a
layer of tissue from the receptacle.
Other fleshy, simple fruits include:
Hesperidium
A heperidium is another specialized berry and includes
the citrus fruits.
The thick peel that has numerous oil cavities is the
exocarp and mesocarp.
Other fleshy, simple fruits include:
Pome
The pome is derived from an inferior ovary.
Seeds are the structures containing the embryonic plant.
Technically, they are mature ovules.
The primary endosperm nucleus
The integuments of the ovule
In cotton, initially after fertilization, the zygote
nucleus divides frequently while the primary
endosperm nucleus divides rapidly to form the
endosperm.
The endosperm is one type of nutrient-rich tissue
that will feed the developing plant when it germinates.
Endosperm
Embryo
cotyledons
The embryo continues to develop,
Cotyledon
Shoot tip
The embryo ultimately develops a shoot tip at one end
and an embryonic root (called a radicle) at the other.
Radicle
The are many variations on the development of the embryo.
The most basic of these is the single cotyledon of
the monocots vs. the 2 cotyledons of the dicots.
2 cotyledons in the dicot,
castor bean
A single cotyledon in the
monocot, onion
The endosperm is a major food storage for the
germinating seed in many monocots.
Both onion (left) and grasses (foxtail, right) have abundant
endosperm in the mature seed.
Germination – growth of the embryo into a plant.
Germination
The cells of the embryo and nutritive parts of
the seed are tightly packed with storage
structures containing starch, proteins, and
lipids.
Foxtail dry seed cell
The first step of germination is imbibition,
Cells rapidly develop a high metabolic rate and the storage bodies diminish.
Germination in garden bean.
The seed is mostly made up of the two cotyledons. Initial stages of
germination, however, involve other parts of the embryo, the
hypocotyl and epicotyl.
The hypocotyl is a structure just at the base of the
cotyledons.
The epicotyl
As the bean seed starts to germinate, the hypocotyl
elongates as the radicle starts to develop into a
root.
The plant stays below ground at first, but the
elongating hypcotyl raises the cotyledons, still
enclosed in the seed coat.
The epicotyl then starts to elongate as the cotyledons
emerge from the seed coat.
The epicotyl enlongates further and the first true foliage leaves develop.
The cotyledons, which are primarily storage, eventually wither as the plant continues to grow.
In grasses like corn, the shoot and root are enveloped by
2 tubular sheaths
Study outline for Chapter 23b-Angiosperms
Label the angiosperm life cycle with the terms below:
sporophyte
gametophyte
anther
filament
pollen sac
pollen
integuments
micropyle
ovule
polar nuclei
synergids
egg
sperm
endosperm
embryo
seed
seedling
stigma
style
ovary
pollen tube
embryo sac
Use the figure above to describe the angiosperm life cycle. Please include an explanation of double fertilization
in your answer.
Study outline for Chapter 23b-Angiosperms
Define the following term of floral characteristics:
complete flower
incomplete flower
perfect flower
imperfect flower
Define the following term of floral characteristics and be able to recognize each characteristic.
regular flower
irregular flower
free floral parts
fused floral parts
superior ovary
inferior ovary
inflorescence
panicle
umbel
compound umbel
spike solitary
disc flowers
ray flowers
What are the 3 types of fruits?
Define simple fruit.
Define aggregate fruit.
Define multiple fruit.
Define dehiscent.
Define indehiscent.
Define the following fruit types and know two examples for each type of fruit.
Dry, simple fruits
legume
follicle
capsule
nut
achene
samara
caryopsis
Which of the fruits listed above are dehiscent?
Which of the fruits listed above are indehiscent?
Fleshy, simple fruits
drupe
berry
hesperidium
pepo
pome
Aggregate fruit
Study outline for Chapter 23b-Angiosperms
Define germination.
Define inhibition.
Define the following terms below and label the images provided:
radicle
cotyledon
epicotyl
hypocotyl
seed coat
foliage leaves
coleoptile
coleorhiza
Which image is a monocot?
Which image is a eudicot?