Unit
Plant Science
Problem Area
Reproduction in Plants
Lesson
Influence of Temperature on
Pollen Germination
Student Learning Objectives
1. Explain sexual reproduction of plants
and its importance.
 2. Explain how pollination occurs and
describe the different types of pollination.
 3. Explain fertilization in angiosperms.
 4. Identify how a common agronomic crop
pollinates and fertilizes.
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Terms
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Cross-pollination
Dioecious
Double fertilization
Endosperm
Fertilization
Gametes
Incompatibility
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Monoecious
Parthenocarpy
Pollination
Self-pollination
Sexual reproduction
Zygote
What is sexual reproduction and why is it
important to plants?
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A. In sexual reproduction, sperm carried in the pollen
from the male flower fuses with the egg in the female
part of the flower. Both contribute to the genetic makeup
of the new plant.
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B. Most plants reproduce their own kind in nature by
seeds that are the result of sexual reproduction. The
male sex cell (sperm) and the female sex cell (egg) are
known as gametes. The union of gametes produces the
seed that contains the embryo and stored food.
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C. Understanding plant reproduction has resulted in the
development of plant hybrids that have enabled large
scale agricultural production of food and fiber plants.
How does pollination occur and what are the
different types of pollination?
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Pollination is the transfer of pollen from male to
the female part of the flower.
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A. Plants rely on wind and water to transfer
pollen to the stigma. In addition, plants depend
on animals to help with pollination. Birds,
insects, bats and other animals are attracted to
brightly colored, scented flowers. These animals
transfer pollen from the anthers of the flowers
they visit to the stigmas of other flowers.
 1.
When the pollen of a plant pollinates a flower on the
same plant, it is called self- pollination. Many plants
have this ability to self-pollinate while others do not.
 2. Some plants have incompatibility (self-sterility),
meaning there is a genetic factor preventing pollen
tubes from growing in the style of the same plant.
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B. When the pollen of a plant pollinates the flower on
another plant of the same species, it is said to be
cross-pollination.
C. Once pollen lands on the stigma, it grows a pollen
tube down the style to the ovary. The cell within the
grain of pollen divides to form two sperm nuclei, which
travel down the pollen tube to the embryo sac,
fertilizing the egg.
How does fertilization occur in flowering
plants?
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Fertilization is necessary in flowering plants in
order for the seed to develop.
A. Fertilization unites the single chromosome in
the sperm nucleus with the single chromosome
in the egg nucleus. This enables the fertilized
egg or zygote, to have a complete pair of
chromosomes.
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B. Fertilization occurs when the nucleus of the
sperm unites with the nucleus of the egg. Plant
fertilization is unique because the sperm
contains two nuclei. Flowering plants have
double fertilization. One sperm nucleus unites
with the egg nuclei to produce a zygote. The
second sperm nucleus unites with the nuclei of
the embryo sac to develop into the endosperm
or food storage tissue.
C. Formation of fruit without the stimulation of
pollination and fertilization is also a possibility.
This is known as parthenocarpy.
How does a common agronomic crop
pollinate and fertilize?
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A. Corn requires specific requirements for
successful production.
B. The silk and tassel are the female and male
reproductive parts of the corn plant.
C. The silk is the female reproductive part and the
tassel is the male reproductive part.
D. Plants such as corn are monoecious meaning
they have separate staminate and pistillate flowers
on the same plant. Dioecious plants, such as
soybeans, have staminate and pistillate flowers on
separate plants.
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E. Pollen shed usually begins two to three days prior to
silk emergence and continues for five to eight days with
peak shed on the third day.
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F. The tassel is usually fully emerged and stretched out
before any pollen is shed. Pollen shed begins at the
middle of the central spike of the tassel and spreads out
later over the whole tassel with the lower branches last
to shed pollen.
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G. Pollen grains are borne in anthers, each of which
contains a large number of pollen grains. The anthers
open and the pollen grains pour out in early to mid
morning after dew has dried off the tassels. Pollen is
light and is often carried considerable distances by the
wind.
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H. Pollen shed is not a continuous process. It stops when
the tassel is too wet or too dry and begins again when
temperature conditions are favorable. The optimum
temperature for corn growth is 70 to 86 degrees F.
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I. Under favorable conditions, pollen grain remains viable
and enters the female flower (ovule).
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J. Pollen of a given plant rarely fertilizes the silks of the
same plant. Under field conditions other plants in the field
pollinate 97% or more of the kernels produced by each
plant.
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K. The amount of pollen is rarely a cause of poor kernel
set. Shortages of pollen are usually only a problem under
conditions of extreme heat and drought. Poor seed set is
more often associated with poor timing of pollen shed with
silk emergence.
Review/Summary
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What is sexual reproduction and why is it
important to plants?
How does pollination occur and what are the
different types of pollination?
How does fertilization occur in flowering plants?
How does a common agronomic crop pollinate
and fertilize?