Download Grade 11 University Biology

Grade 11 University Biology
Plant Reproduction
Section 14.1 Pages 582-592
For a very detailed description of the life of plants, see
http://www.sebring.k12.oh.us/McKinley_Jr__Sr__High_School/Naples/7th/chap10.pdf
Seedless Reproduction
 Seedless plants include all non-vascular plants and some vascular plants (i.e., ferns)
 Plants such as ferns and mosses do not produce seeds; rather, they grow from spores
 The sporophyte stage of these plants produces haploid spores inside spore cases. When the
case breaks, the spores are released and moved by either wind or water. The spores may grow
into plants that can produce sex cells. (i.e., male and female gametophytes)
 Non-vascular plants do NOT have vascular bundles (...in other words, they cannot transport
water throughout the plant). Instead, water just flows from cell to cell.
Moss Life Cycle
 Starting in the upper left corner of the
illustration, the spores (n) are released
from the moss capsule.
 On suitable ground, a spore starts to
grow and develops into a small green
shoot called a protonema.
 The protonema grows buds that
become the familiar leafy green stems
of a moss. This phase of the
moss lifecycle is termed the
gametophyte. The gametophyte may
be male (n) or female (n).
 Within some leaves of the gametophyte,
special structures develop into male and
female sex organs. The male part is
called the Antheridium (n) and the
female part the Archegonium (n)
 Inside the Antheridium, sperm are
produced. They have tails (flagella) so
they can swim, in a film of water, to the Archegonium.
 The sperm are attracted to the Archegonium by chemicals released into the film of water.
 Once reaching the Archegonium, the sperm swim down the Archegonium’s neck to reach and
fertilize the egg
 The fertilized egg (2n) develops into a structure called the sporophyte. The sporophyte
consists of a stem or seta and a capsule in which vast numbers of spores, via meiosis, are
produced. During the growth period, the capsule is covered by a thin protective layer
(calyptras).
 When the spores are nearing maturity, the calypra falls off revealing a cap or operculum that
keeps the spores from being released. At maturity, the operculum falls off and, usually in dry
weather, the spores are shaken out of the capsule and dispersed by the wind.
 On the ground, the spores begin to produce new gametophytes...and the cycle is repeated.
Fern Life Cycle (Vascular Seedless Plants)
 Fern leaves are fronds that grow from an
underground stem called a rhizome. The
roots also grow from the rhizome
 Fern do not flower; rather, they produce
spores and grow with a gametophyte
intermediate stage.
 Different from the moss, the fern
sporophyte produces its own food from
photosynthesis.
 Spores are produced on the underside of
the frond in a structure called a sori
(...sometimes mistaken for disease)
 Once released, the spores fall to the
ground. If they land on damp soil, the
spore grows into a small, green, heartshaped prothallus (the gametophyte).
 Male and female reproductive structures
form on the prothallus.
 Using water, the male sperm swims to the
egg, and fertilization occurs to produce a
zygote
 The zygote grows into the familiar fern plant.
 Meiosis occurs to produce spores inside a spore case
 Once mature, the spores are ejected and fall to the ground...and the cycle is repeated.
Sexual Reproduction
Cost and Benefits of Sexual Reproduction
 Populations have a high level of genetic diversity. If environmental conditions change, the
chance of some individuals will survive is increased.
 The products of sexual reproduction are seeds. Seeds can be dispersed far from the parent
plant. Thus, seeds may find better growing conditions, inhabit new areas and experience less
competition for resources
 Seeds can remain dormant for long periods and germinate when growing conditions are
favourable. This increases the
chance of survival.
Gymnosperms
 Gymnosperm means “naked seed.”
In other words, seeds are NOT
enclosed in an ovary as in the
flowering plants; rather, seeds grow
on the surface of a modified leaf in a
strobilus or cone. Thus,
gymnosperms are conifers (e.g., pine,
cedar).
 Conifers produce both male and
female cones.
 In the male cone, haploid cells called
microspores are produced by meiosis.
Each microspore develops into a
pollen grain containing a male
gametophyte.
 In the female cone, meiosis produces
megaspores that give rise to egg-producing female gametophytes.
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Pollination (i.e., transfer of male pollen grains to the female ovule) is wind pollination.
Sticky resin and the cone’s shape guide the pollen to the ovule.
Once at the ovule, the pollen grain grows a pollen tube. As the tube grows, the haploid nucleus
divides by mitosis to produce two haploid sperm nuclei. One sperm fertilizes the egg to produce
a diploid zygote. The other sperm degrades....THUS “single fertilization.”
Upon fertilization, the ovule develops the seed structures (i.e., seed coat and endosperm) and the
zygote develops into the embryo.
Female cones remain on the parent plant until the seeds mature.
If the seed germinates, it grows into a sporophyte and the cycle is repeated.
Alternation of generations is involved in gymnosperm reproduction. They are all heterosporous:
the microspores are shed as pollen; whereas, the megaspore germinates in the strobilus to
produce the female gametophyte. The archegonia is fertilized by sperm from the male
gametophyte and the zygote grows to produce an embryo which is enclosed in a seed coat of
tissue from the parent plant.
Angiosperms
 Angiosperms are flowering plants.
 Most angiosperms are
terrestrial...and thus, they lack
mobility. Thus, the flower is very
important to angiosperm fertilization.
 Meiosis in the sporophyte generation
produces two kinds of spores: (1)
microspores which develop into the
male gametophyte, and (2)
megaspores which develop into the
female gametophyte. Both
gametophytes are produced in the
flower.
 Monocots have “imperfect flowers”
on the same plant. That is, one
flower has male parts while a
different flower has only female
parts. Dicots flowers ON THE
SAME PLANT are either male or
female.
 The male part of the plant is the
stamen with two parts: (1) anther
produces pollen grains, and (2)
filament gives support. Meiosis
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produces pollen grains.
The female part is the carpel with three parts: (1) stigma with a sticky surface as a landing site
for pollen grains, (2) style is a tube and (3) ovary containing ovules. Meiosis produces four
haploid cells...one megaspore and three smaller cells that degenerate. The megaspore
undergoes three mitotic divisions to produce eight nuclei consisting of (1) an egg cell, (2) two
cells that secrete an attractant the guides the pollen tube, (3) two polar nuclei which will develop
into the endosperm after fertilization and (4) three antipodal cells
When a pollen grain reaches the stigma, it germinates into a pollen tube. The germ cell divides by
mitosis forming two sperm cells. The two sperm cells migrate down the pollen tube and into the
female ovule chamber.
At this point, Double Fertilization occurs. One sperm cell fuses with the egg forming the diploid
zygote. The other sperm cell fuses with the polar nuclei forming the endosperm nucleus. Most
angiosperms have two polar nuclei so the endosperm is triploid (3n).
The product of sexual reproduction in angiosperms are seeds contained inside a fruit (...a ripened
ovary)