Reproduction in
Flowering Plants
Flowers are specialized for sexual
reproduction. Meiosis and fertilization
occur in a flower.
Most flowers contain both the male and female
reproductive organs. Flowers with both reproductive
organs are called “perfect or complete flowers”.
Flowers containing only one reproductive organ are called
“imperfect or incomplete flowers”.
Many flowers also have accessory or extra structures,
such as petals and sepals.
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Reproductive parts of a flower:
The stamen is the male reproductive organ of a flower. It
is composed of an anther and a filament.
As a result of meiosis, the diploid (2n) cells of the anther
produce pollen grains which contain monoploid (n) nuclei.
The pistil is the female reproductive organ of a flower. It is
composed of the stigma, style, and the ovary.
During meiosis, the ovary produces ovules, which contain
the monoploid egg nucleus (n).
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Mrs. Degl
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Pollination
Pollination is the transfer of pollen grains from the anther to the stigma.
Pollination may be accomplished by wind, insects, and birds.
In some cases, the colored petals of a flower act as a visual attraction
for insects. Nectar can also act as an attractant.
Self-Pollination is the transfer of pollen from the anther to the stigma
of the same flower or from the anther to the stigma of another flower that is
part of the same plant.
Cross pollination is the transfer of pollen from an anther on one
flower to a stigma of a flower on a different plant. Cross pollination is an
adaptation which causes variation among flowers.
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Pollen
•In flowering plants, the problem of
reproduction in a dry, external
environment is partially solved by the
presence of the thick wall of the pollen
grain.
•The pollen grain wall prevents
dehydration of the contents while it is
transferred to the stigma (female organ).
•After pollination, the pollen grain
germinates (is activated) on the stigma
and forms a pollen tube, which extends
to the ovule.
•Sperm nuclei is formed at this time, in
the pollen tube, from the monoploid (n)
nucleus in the pollen grain.
•The pollen tube is an adaptation for
internal fertilization.
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Flower Fertilization and Embryo Development.
•The union or fusion of the male and female nuclei in the ovule results in a
zygote.
•The zygote continues to develop into an embryo.
•The ripened ovule, with the embryo, develops into the seed.
•The seed consists of a seed coat, which develops from the outer
coverings of the ovule and embryo.
•The ripened ovary develops into the fruit.
•The plant embryo consists of three parts: hypocotyl, epicotyl, and
cotyledon.
(1 cotyledon = monocot)
(2 cotyledons = dicot)
(cotyledon)
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Germination and Growth
Fruits are specialized structures that
which aid in seed dispersal. Seeds
develop inside the fruit. If the
temperature and moisture and oxygen
levels are sufficient, the dispersed
seeds will germinate (activate and
grow).
Growth in most plants occurs in the meristems.
The organs of a plant are developed in the meristems.
Apical Meristems are found in the tips of roots and stems and cause the
plant to grow in length.
Lateral Meristems (Cambium) are between the xylem and phloem and
cause the plant to grow in diameter (get wider).
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