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Index
S.no Contents Pg.no

1. Objective 2

2. Materials 3

3. Background Information 4

4. Theory 5

5. Structure of a Flower 6

6. Process of Sexual Reproduction 7

7. Outbreeding Devices 10

8. Double Fertilization 11

9. Experiments 16

10. Applications 19

11. Conclusion 20

12. Bibliography 21
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Objective
To understand the process of sexual reproduction in
flowering plants, study the structure of flowers, and
explore the mechanisms of pollination and fertilization.
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Materials
● Fresh flowers (e.g., lily, hibiscus)
● Microscope
● Slides and cover slips
● Staining solution (e.g., iodine)
● Paintbrush
● Water
● Petri dish
● Notebook and pencil
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Background Information
Sexual reproduction in flowering plants involves
the formation of seeds through the fusion of male and
female gametes. This process includes pollination,
where pollen is transferred from the male anther to the
female stigma, followed by fertilization, where the male
gamete fuses with the female ovule
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Theory
● Pollination:
The transfer of pollen from an anther to a stigma.
● Fertilization:
The fusion of male and female gametes to form a
zygote, which develops into a seed.
● Types of Pollination:
1.Self-Pollination:
Pollen from the same flower or plant.
2.Cross-Pollination:
Pollen from a different flower or plant.
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Structure of Flower
● Sepals: Protect the flower bud before it opens.
● Petals: Often colorful and attract pollinators.
● Stamens: The male reproductive parts consisting
of anthers and filaments.
● Carpels/Pistils: The female reproductive parts
consisting of stigma, style, and ovary.
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Process of Sexual Reproduction

Pollination
● Self-Pollination: Pollen is transferred to the stigma
of the same flower or another flower on the same
plant.
● Cross-Pollination: Pollen is transferred to the
stigma of a flower on a different plant of the same
species, often facilitated by wind, water, or
animals.
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Fertilization
● Step 1: Pollen lands on the stigma and germinates,
forming a pollen tube.
● Step 2: The pollen tube grows down the style
towards the ovary.
● Step 3: The sperm cells travel through the pollen
tube to reach the ovule.
● Step 4: One sperm cell fuses with the egg cell to
form a zygote, while the other fuses with two polar
nuclei to form the endosperm (double fertilization).
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Double Fertilization
Double fertilization is a unique and complex
process in the reproductive cycle of flowering plants
(angiosperms). It involves two separate fertilization
events within the female reproductive organ of the
plant
First Fertilization Event: One of the two sperm cells
fuses with the egg cell, resulting in the formation of a
diploid (2n) zygote. This zygote will eventually develop
into the embryo of the seed.
Second Fertilization Event: The other sperm cell
fuses with the two haploid polar nuclei located in the
central cell of the embryo sac. This fusion forms a
triploid (3n) cell called the primary endosperm cell,
which will develop into the endosperm. The endosperm
serves as a nutritive tissue that supports the
developing embryo.
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Outbreeding Devices
Outbreeding devices are mechanisms that
flowering plants have evolved to promote cross-
pollination (outcrossing) and reduce the likelihood of
self-pollination (inbreeding). These mechanisms
enhance genetic diversity and improve the adaptability
and survival of plant species. Here are some key
outbreeding devices:

1. Dichogamy

Dichogamy refers to the temporal separation of

male and female reproductive organ maturity within a
single flower or between flowers on the same plant.
There are two main types:

● Protandry: The male anthers mature and release

pollen before the female stigmas are receptive.
This ensures that pollen is dispersed before the
stigma of the same flower can be fertilized.
Examples include many species of the sunflower
family (Asteraceae) and carrot family (Apiaceae).
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● Protogyny: The female stigmas mature and

become receptive before the male anthers release
pollen. This also reduces the chance of self-
fertilization. Examples include some species of
magnolias and arum lilies.

2. Herkogamy

Herkogamy is the spatial separation of anthers and

stigmas within the same flower to reduce the likelihood
of self-pollination. There are different types of
herkogamy:

● Approach Herkogamy: The stigma is positioned

above the anthers, so pollinators contact the
stigma before touching the anthers.
● Reverse Herkogamy: The anthers are positioned
above the stigma, promoting pollen transfer to
other flowers before the stigma is contacted.
● Enantiostyly: Flowers exhibit left-right
asymmetry with anthers and stigmas positioned on
opposite sides, promoting cross-pollination.

3. Self-Incompatibility (SI) Systems

Self-incompatibility is a genetic mechanism that

prevents self-fertilization and promotes outcrossing. It
involves recognition and rejection of self-pollen based
on genet
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markers

● Gametophytic Self-Incompatibility (GSI): The

incompatibility is determined by the haploid
genotype of the pollen. If the pollen's S-allele
matches the S-allele of the stigma, pollen tube
growth is inhibited. Examples include many species
of the nightshade family (Solanaceae), such as
tomatoes and potatoes.
● Sporophytic Self-Incompatibility (SSI): The
incompatibility is determined by the diploid
genotype of the pollen parent. The stigma surface
recognizes and rejects pollen based on specific
surface proteins. Examples include members of the
mustard family (Brassicaceae), such as cabbage
and broccoli.

4. Heterostyly

Heterostyly is the presence of different flower

morphs within a species, each with distinct lengths of
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stamens and pistils. This structural variation promotes

cross-pollination between different morphs:

● Distyly: Species have two flower morphs, one with

long styles and short stamens (pin flowers), and
the other with short styles and long stamens
(thrum flowers). This promotes cross-pollination as
pollinators transfer pollen from one morph to the
stigma of another. Examples include primroses
(Primula) and some species of flax (Linum).
● Tristyly: Species have three flower morphs, each
with different combinations of short, medium, and
long stamens and styles. Examples include some
species of the water hyacinth (Eichhornia).

5. Dioecy and Monoecy

● Dioecy: Species have separate male and female

plants, ensuring cross-pollination since individual
plants produce only male or female flowers.
Examples include willow(Salix) and holly.
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● Monoecy: Species have both male and female

flowers onthe same plant but in different locations,
reducing thelikelihood of self-pollination. Examples
include corn(Zeamays) and cucumbers (Cucumis
sativus).

6. Unisexual Flowers

Unisexual flowers are either male or female,

preventing self pollination within the same flower. Plants may
be monoecious or dioecious

● Male Flowers: Produce only pollen and are

typically found on the same or different plants as
female flowers.
● Female Flowers: Contain only the pistil and can
only receive pollen from male flowers.
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7. Temporal Flower Opening

Some plants stagger the opening times of their

flowers to promote cross-pollination. Flowers may open
at different times of the day or in different seasons,
reducing the chances of self-pollination.

8. Pollinator Behavior

Certain flowers are adapted to attract specific

pollinators whose behavior promotes cross-pollination.
For example, flowers may have specific colors, shapes,
scents, or nectar rewards that attract bees, birds, bats,
or other pollinators, ensuring pollen transfer between
different plants.

9. Mechanical Barriers

Some flowers have physical barriers that make it

difficult for self-pollination to occur. For example, the
structure of the flower may prevent the pollen from
reaching the stigma of the same flower.
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Experiments
Experiment 1: Observing Pollen Grains
● Objective: To observe and identify pollen grains
from different flowers.
● Materials: Fresh flowers, microscope, slides,
cover slips, staining solution, paintbrush.
● Procedure:
1. Collect pollen from the anther using a
paintbrush.
2. Place the pollen on a slide and add a drop of
staining solution.
3. Cover with a cover slip and observe under the
microscope.
4. Draw and label the pollen grains observed.
● Observation: Note the size, shape, and structure
of the pollen grains.
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Experiment 2: Germination of Pollen on Stigma

● Objective: To observe the germination of pollen
grains on a stigma.
● Materials: Fresh flowers, microscope, slides,
cover slips, water, petri dish.
● Procedure:
1. Collect a stigma with some pollen on it from a
flower.
2. Place the stigma on a slide and add a drop of
water.
3. Cover with a cover slip and observe under the
microscope.
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4.Look for pollen tubes emerging from the pollen

grains.
● Observation: Record the presence of pollen tubes
and measure their length.
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Applications
● Agriculture: Understanding pollination and
fertilization can help improve crop yields and
hybrid plant development.
● Horticulture: Knowledge of flower structure and
reproduction is essential for breeding new plant
varieties.
● Conservation: Understanding plant reproduction
aids in the conservation of endangered plant
species.
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Conclusion
Summarize the process of sexual reproduction in
flowering plants, highlighting the importance of
pollination and fertilization in the formation of seeds
and the continuation of plant species.
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Bibliography
● Botany textbooks
● Scientific journals on plant biology
● Online educational resources on plant reproduction

 "Biology of Plants" by Peter H. Raven,

 "Plant Systematics
 "The Flowering Process
 "Pollination and Fertilization in Flowering Plants"
 "Plant Reproductive System" on Encyclopaedia
 "Reproduction in Flowering Plants"
 Nature journal - Plant Reproduction