Transcript The Life Cycle of Angiosperms

Tuesday, July 21, 2015
THE LIFE CYCLE OF
ANGIOSPERMS
1
Packet #75
Chapter #38
Tuesday, July 21, 2015
INTRODUCTION
Angiosperms are the
predominant plant
species on the planet.
 Unlike gymnosperms,
these plants produce
seeds that have a
covering.

2
Tuesday, July 21, 2015
LIFE CYCLE OF ANGIOSPERM
Figure 38.2 (More Detail)
Page 772
In the angiosperm,
the sporophyte
generation is
dominant
 Gametophytes are
extremely reduced in
size and nutritionally
dependent on the
sporophyte generation
 Flowering plants are
hetereosporous

3
Tuesday, July 21, 2015
FIGURE 38.4
THE DEVELOPMENT OF ANGIOSPERM
GAMEOPHYTES
4
Pollen sac
(microsporangium)
(a) Development of a male gametophyte
(pollen grain)
1
Each one of the
microsporangia
contains diploid
microsporocytes
(microspore
mother cells).
2 Each microsporocyte divides by
meiosis to produce
four haploid
microspores,
each of which
develops into
a pollen grain.
3
Figure 38.4a
Tuesday, July 21, 2015
FIGURE 38.4
DEVELOPMENT OF POLLEN GRAINS
A pollen grain becomes a
mature male gametophyte
when its generative nucleus
divides and forms two sperm.
This usually occurs after a
pollen grain lands on the stigma
of a carpel and the pollen
tube begins to grow. (See
Figure 38.2b.)
Microsporocyte
MEIOSIS
Microspores (4)
Each of 4
microspores
MITOSIS
Generative
cell (will
form 2
sperm)
Male
Gametophyte
(pollen grain)
20
75
m
Nucleus
of tube cell
m
Ragweed
pollen
grain
KEY
to labels
Haploid (2n)
Diploid (2n)
5
Tuesday, July 21, 2015
FIGURE 38.4
DEVELOPMENT OF EMBRYO SACS
(b) Development of a female gametophyte
(embryo sac)
Megasporangium
Ovule
MEIOSIS
Megasporocyte
Integuments
Micropyle
Surviving
megaspore
Female gametophyte
(embryo sac)
MITOSIS
Ovule
Antipodel
Cells (3)
Polar
Nuclei (2)
Egg (1)
Integuments
100
Haploid (2n)
Diploid (2n)
m
Key
to labels
Synergids (2)
Embryo
sac
1 Within the ovule’s
megasporangium
is a large diploid
cell called the
megasporocyte
(megaspore
mother cell).
2 The megasporocyte divides by
meiosis and gives rise to four
haploid cells, but in most
species only one of these
survives as the megaspore.
3 Three mitotic divisions
of the megaspore form
the embryo sac, a
multicellular female
gametophyte. The
ovule now consists of
the embryo sac along
with the surrounding
integuments (protective
tissue).
Figure 38.4b
6
Tuesday, July 21, 2015
LIFE CYCLE OF ANGIOSPERM


Each microspore develop
into a pollen grain.
Immature male
gametophytes are contained
within pollen grains.


Each pollen grain has two
haploid (n) cells.
One of each four
megaspores produced
during meiosis develops into
an embryo sac (female
gametophyte).
Embryo sac contains seven
cells with eight nuclei
 The egg cell and the
central cell, which
contains two polar nuclei,
participate in
fertilization.

7
Tuesday, July 21, 2015
LIFE CYCLE OF ANGIOSPERM
Pollen released from
the anther
 Pollen is carried to the
sticky stigma
 Flowers can selfpollinate or crosspollinate.


Transfer of pollen
from flowers of one
plant to flowers of
another plant is called
cross-pollination
8
Tuesday, July 21, 2015
LIFE CYCLE OF ANGIOSPERM



Pollen grain germinates
after it sticks to the
stigma.
Pollen grain now contains
the mature male
gametophyte and extends
a tube down through the
style.
After it reaches the ovary,
the pollen tube penetrates
the microphyle and
discharges two sperm
cells into the female
gametophyte (embryo sac)

Results in double
fertilization
9
Tuesday, July 21, 2015
POLLEN TUBE
10

Double Fertilization
Results in the formation
of a diploid zygote and
triploid endosperm
 One sperm nucleus fuses
with the egg to form a
diploid zygote.
 The other sperm nucleus
fuses with the two nuclei
if the female
gametophyte



Tuesday, July 21, 2015
LIFE CYCLE OF ANGIOSPERM
Cell is now triploid (3n).
Characteristic of
flowering plants.
11

Double fertilization
ensures the
endosperm will
develop only in ovules
where the egg has
been fertilized

Tuesday, July 21, 2015
FIGURE 38.6
DOUBLE FERTILIZATION
Prevents the
angiosperms from
wasting resources
12
After double
fertilization, the ovule
matures into a seed.
 The zygote develops
into the sporophyte
embryo with a
rudimentary root and
either one or two seed
leaves (cotyledons—
monocots vs. dicots)

Tuesday, July 21, 2015
LIFE CYCLE OF ANGIOSPERM
13





Seed consists of the embryo,
endosperm, sporangium and
a seed coat.
An ovary develops into a
fruit as its ovules develop
into seeds.
Dispersal occurs via wind or
animals
Seed germinates if the
environmental conditions
are favorable.
Seed coat ruptures, the
embryo emerges as a
seedling and uses the stored
food in the endosperm and
cotyledons to begin growth.
Tuesday, July 21, 2015
LIFE CYCLE OF ANGIOSPERM
14
Tuesday, July 21, 2015
MECHANISMS TO PREVENT
SELF-POLLINATION
(SELFING!)
15
Chapter 38


Some flowers selffertilize but most
angiosperms have
mechanism that prevent
“selfing.”
Dioecious plants

Unisexual


Tuesday, July 21, 2015
INTRODUCTION I
Ackee {Barbados}—
Ginnup {Jamacia}
Bisexual flowers
Stamens and carpels
mature at different times
 Stamens and carpels are
arranged in a way that
makes self-pollination
unlikely

16

AKA Self-incompatibility
Most common method that plants use to prevent
“selfing”
 Some plants recognize their own pollen and that of
closely related individuals



Tuesday, July 21, 2015
INTRODUCTION II
BIOCHEMICAL BLOCKING
Hmmm!
Biochemical block prevents pollen from completing
its development and fertilizing the egg
17
Tuesday, July 21, 2015
REVIEW
18
Imagine that…plants which are more simplistic
organisms appear to have more complex
reproductive cycles.

Students

List potential examination questions and/or here, and
on following slides, based on the packet.
Tuesday, July 21, 2015
REVIEW
19