Plant Reproduction
• Like all other living things, plants also need to
reproduce to produce more plants.
• Plants can reproduce asexually or sexually.
• Botanists and farmers have been able to
interfere in the reproductive process of plants
to produce new plants with desirable
characteristics.
• This has had an impact on diversity and
quality plant food production.
Reproduction in Nonvascular Plants
• Nonvascular plants can reproduce asexually through
the process of vegetative reproduction. This occurs
when part of the plant breaks off and a new identical
plant develops.
• Most nonvascular plants reproduce sexually. The male
gamete is called an antheridium and it produces a
flagellated sperm. The female gamete is called an
archegonium and it produces a single egg.
• A moist area is needed for reproduction to occur.
Water allows the male sperm cells to swim from the
antheridium to the archegonium.
• The fertilized egg cell divides by mitosis and develops
into an embryonic sporophyte within the archegonium.
• Most plants have a life cycle that includes a
diploid generation, sporophyte, and a haploid
generation, gametophyte.
• The gametophyte generation is the dominant
generation in nonvascular plants.
• The sporophyte grows into a long stalk but
remains attached to the archegonium.
• A sporangium forms at the tip of
the long stalk and haploid spores
develop through meiosis.
• The sporangium bursts and the
spores scatter and they
germinate by mitosis forming
mature gametophytes.
Reproduction in Vascular plants
• Gymnosperms produce cones that are either
male cones or female cones.
• Male cones are small and generally found in
clusters.
• The male cones produce and release haploid
pollen cells that resemble yellow dust.
• Female cones are also
small but are very sticky.
• This allows the pollen to
adhere to the cone so that
fertilization can occur.
• When the pollen grain
attaches to the female cone,
it must travel to the female
gametophyte where the
archegonium houses the egg
cell.
• The pollen grain travels to
the opening of the ovule
called the micropyle and
attaches itself to the
nucellus.
• Here it will grow and develop
into a male gametophyte.
• The male gametophyte releases haploid
sperm cells that will eventually fertilize the
female egg cell to produce a diploid zygote.
• The zygote grows and develops into a seed
within the female gametophyte.
• It is protected by a layer of tissue called the
integument that will become the seed coat.
• Soon enough the seeds will be released and
germination will occur.
Reproduction in Angiosperms
Flowering plants usually contain both the female and male
parts. The female area of the plant is called the carpel and
it includes the stigma, style, ovary, and ovules or eggs. The
male part of the flower is called the stamen and it includes
the filament, anther, and pollen or sporangium.
• When a pollen grain reaches the stigma, it
germinates into a pollen tube.
• The germ cell divides by mitosis forming two
sperm cells.
• These sperm cells migrate down the pollen
tube as it grows through the style, micropyle,
and into the ovule chamber.
• The pollen tube enters the ovule through the
micropyle and it breaks open.
• One sperm cell fertilizes an egg cell forming a
diploid zygote.
• The other sperm cell fuses with a polar egg
cell (non-functioning) to form the endosperm.
• This is called double fertilization.
• The endosperm will provide nourishment to
the developing seed.
• After fertilization, each ovule develops into a
seed.
• The ovule covers and protects each seed.
Germination
• When a seed is released, it may not germinate
immediately. Growth may be delayed until
favourable conditions are present. Most seeds
will experience a period of dormancy. This period
may be a couple of days or even a couple of years
before germination starts.
• Germination begins when a hormone called
gibberellin is released into the seed from the
embryo. This hormone activates enzymes that
break down starch into smaller molecules to be
used as a source of energy for the embryo.
• As this occurs, water moves into the seed through
osmosis and the seed coat begins to swell.
• Often small cracks will result from the swelling of the
seed and this allows oxygen to enter the seed.
• With oxygen present, the embryo can undergo
aerobic cellular respiration and produce even more
energy in the form of ATP.
• The tip of the radicle
emerges out of the seed
first and elongates
downwards forming the
roots.
• The hypocotyl emerges
next and it forms a hook
and elongates upwards
and becomes the stem.
• Initially the cotyledons act
• The hypocotyl grabs the like leaves and carry out
cotyledon as it moves
photosynthesis, but as the
upwards towards light.
plant develops, true leaves
form and the cotyledon fall
off.
Artificial Reproduction
• The need to produce more food and
commercially viable plant products has caused
horticulturists and farmers to influence the
natural fertilization process of plants.
• Here are a few modified processes of plant
reproduction.
• Selective breeding has been used by farmers
for many years.
• In this process of sexual reproduction, farmers
choose plants that have desirable qualities
and only allow them to fertilize each other.
• Over time, the desirable qualities will be
present in all the seeds and the unfavourable
characteristics will be eliminated.
• This procedure is similar to what Gregor
Mendel did in order to get his pure bred
plants.
• Wheat, corn, and bananas are a few examples
of plants that have been selectively bred.
• Cutting is a form of asexual reproduction that
is very easy to perform.
• If there is plant that has desirable traits you
can simply cut a piece of the plant that
includes the stem and place it in water or soil.
• Tissue will start to develop from the cut end of
the stem.
• This tissue is called a callus and will eventually
develop into roots.
• This new plant is genetically identical to the
parent plant it came from.
• Grafting is a form of asexual reproduction that
can only be done with plants that have vascular
cambium, the tissue between xylem and phloem
cells in dicot plants.
• A bud (scion) from a plant that has desirable
characteristics is grafted or attached to the root
or stem (stock) of another plant.
• At the site of attachment, the
cambium of the scion fuses with the
cambium of the stock.
• This process allows farmers to grow
genetically identical trees.
• Apples, grapes, plums, and peaches
are all produced by grafting.
• The Macintosh apple was discovered in Ontario in
1811 by John Macintosh. Learn about the history of
the Macintosh apple.
Homework
• There are many good sites that animate the
process of fertilization in gymnosperms. Life
cycle of a Conifer is one that you can try.
• There are many good animations that show
how fertilization occurs in angiosperms. You
should view this Double Fertilization Video.