Sexual reproduction in flowering plants is a complex biological process that ensures the production of genetically diverse offspring. It involves the fusion of male and female gametes, leading to the formation of seeds, which develop into new plants. Unlike asexual reproduction, sexual reproduction involves meiosis, pollination, fertilization, and seed formation. This process not only maintains species continuity but also promotes variation, which is crucial for adaptation and evolution.
Sexual Reproduction in Flowering Plants – Class 12 Biology Notes, MCQs & Questions”
Structure of a Flower
Understanding sexual reproduction in flowering plants begins with knowing the structure of a flower. A typical flower consists of both male and female reproductive organs along with other supportive structures.
Male Reproductive Organ – Stamen
The stamen is the male part of the flower and consists of:
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Anther: Produces pollen grains which contain male gametes (sperm cells).
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Filament: A stalk that supports the anther.
Female Reproductive Organ – Carpel/Pistil
The carpel or pistil is the female part of the flower and includes:
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Stigma: The sticky tip that captures pollen grains.
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Style: A tube-like structure that connects the stigma to the ovary.
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Ovary: Contains ovules, each of which can develop into a seed after fertilization.
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Ovule: Contains female gametes (egg cells).
Other Parts of a Flower
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Petals: Often colorful to attract pollinators.
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Sepals: Protect the developing flower bud.
Pollination
Pollination is the transfer of pollen grains from the anther to the stigma of a flower.
Types of Pollination
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Self-Pollination: Pollen from the anther falls on the stigma of the same flower or another flower of the same plant.
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Cross-Pollination: Pollen from the anther of one flower is transferred to the stigma of another flower on a different plant.
Agents of Pollination
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Abiotic: Wind (anemophily) and water (hydrophily).
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Biotic: Insects (entomophily), birds (ornithophily), and animals.
Fertilization
Fertilization is the fusion of male and female gametes to form a zygote.
Process of Fertilization
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Pollen Germination: A pollen grain on the stigma germinates and forms a pollen tube.
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Pollen Tube Growth: The pollen tube grows through the style toward the ovule.
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Syngamy: Male gamete fuses with the female gamete (egg) inside the ovule to form a zygote.
Double Fertilization
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Unique to angiosperms.
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One male gamete fuses with the egg to form the zygote.
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The second male gamete fuses with two polar nuclei to form the triploid endosperm, which nourishes the developing embryo.
Development of Seeds and Fruits
Seed Formation
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After fertilization, the zygote develops into an embryo.
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The ovule becomes the seed, and the surrounding ovary tissue develops into the fruit.
Fruit Formation
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Fruits protect seeds and aid in their dispersal.
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Types of fruits include simple, compound, and multiple fruits.
Seed Dispersal
Seeds are dispersed to reduce competition and promote colonization. Common methods include:
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Wind: Lightweight seeds like cotton.
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Water: Coconut seeds.
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Animals: Burdock seeds cling to fur, or fruits are eaten and excreted.
Importance of Sexual Reproduction in Flowering Plants
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Produces genetic variation, which helps plants adapt to changing environments.
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Ensures survival of species through seed formation.
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Enables evolution through recombination of genes.
Multiple Choice Questions (MCQs)
Q1. The male gamete in flowering plants is present in:
a) Ovule
b) Stigma
c) Pollen grain
d) Ovary
Answer: Pollen
Q2. The female gamete in flowering plants is:
a) Pollen grain
b) Egg cell
c) Stigma
d) Style
Answer: Egg
Q3. Pollination is the transfer of pollen from:
a) Stigma to anther
b) Ovule to stigma
c) Anther to stigma
d) Style to ovary
Answer: Anther
Q4. Self-pollination occurs in:
a) Different plant species
b) Same flower or same plant
c) Different genera
d) Same family but different species
Answer: Same
Q5. Cross-pollination requires:
a) Same flower
b) Same plant
c) Different plants
d) No pollen
Answer: Different
Q6. The sticky part of the pistil that receives pollen is:
a) Ovary
b) Stigma
c) Style
d) Sepal
Answer: Stigma
Q7. The tube through which pollen travels to reach the ovule is called:
a) Style
b) Pollen tube
c) Filament
d) Ovary
Answer: Tube
Q8. Fertilization results in the formation of a:
a) Zygote
b) Pollen grain
c) Endosperm
d) Ovule
Answer: Zygote
Q9. Double fertilization occurs in:
a) Gymnosperms
b) Bryophytes
c) Angiosperms
d) Pteridophytes
Answer: Angiosperms
Q10. The triploid tissue formed after double fertilization is:
a) Zygote
b) Embryo
c) Endosperm
d) Cotyledon
Answer: Endosperm
Q11. Ovules develop into:
a) Fruit
b) Seed
c) Pollen
d) Flower
Answer: Seed
Q12. Ovary develops into:
a) Seed
b) Fruit
c) Pollen
d) Stigma
Answer: Fruit
Q13. Anemophily refers to pollination by:
a) Birds
b) Insects
c) Wind
d) Water
Answer: Wind
Q14. Entomophily refers to pollination by:
a) Birds
b) Insects
c) Water
d) Wind
Answer: Insects
Q15. Fertilization in flowering plants takes place in the:
a) Stigma
b) Style
c) Ovule
d) Anther
Answer: Ovule
Q16. The stalk of a stamen is called:
a) Anther
b) Filament
c) Style
d) Pedicel
Answer: Filament
Q17. Sepals primarily function to:
a) Attract pollinators
b) Protect flower bud
c) Produce gametes
d) Disperse seeds
Answer: Protect
Q18. Petals mainly function to:
a) Protect ovule
b) Produce pollen
c) Attract pollinators
d) Support ovary
Answer: Attract
Q19. Seeds dispersed by water are called:
a) Anemochory
b) Hydrochory
c) Zoochory
d) Autochory
Answer: Hydrochory
Q20. Seeds dispersed by animals are called:
a) Autochory
b) Anemochory
c) Zoochory
d) Hydrochory
Answer: Zoochory
Short Answer Questions
Q1. Define pollination.
Answer: Pollination is the transfer of pollen grains from the anther to the stigma of a flower, enabling fertilization.
Q2. What is self-pollination?
Answer: Self-pollination occurs when pollen from the anther of a flower falls on the stigma of the same flower or another flower of the same plant.
Q3. What is cross-pollination?
Answer: Cross-pollination is the transfer of pollen from the anther of one flower to the stigma of a flower on a different plant of the same species.
Q4. What is double fertilization?
Answer: Double fertilization is a unique process in angiosperms where one male gamete fuses with the egg to form a zygote and the other fuses with two polar nuclei to form triploid endosperm.
Q5. Name the female reproductive part of a flower.
Answer: The female reproductive part of a flower is called the carpel or pistil, which consists of stigma, style, and ovary.
Long Answer Questions
Q1. Describe the structure of a flower and its role in sexual reproduction.
Answer: A flower consists of male (stamens) and female (carpel/pistil) reproductive organs. Stamens have anthers, which produce pollen, and filaments that support them. The carpel includes the stigma, which captures pollen; the style, which connects stigma to ovary; and the ovary, which contains ovules. Petals attract pollinators while sepals protect the flower bud. Together, these structures ensure the transfer of gametes, fertilization, and seed formation, which are essential for sexual reproduction.
Q2. Explain the process of fertilization in flowering plants.
Answer: Fertilization starts when pollen grains land on the stigma and germinate, forming a pollen tube that grows through the style toward the ovule. One male gamete fuses with the egg to form a zygote, while in angiosperms, the second male gamete fuses with two polar nuclei to form triploid endosperm. The zygote develops into an embryo, ovules into seeds, and ovary into fruit, ensuring the next generation of plants.
Q3. What is the importance of sexual reproduction in flowering plants?
Answer: Sexual reproduction produces genetic variation, which helps plants adapt to changing environments. It ensures species continuity, allows evolution through gene recombination, and results in the formation of seeds and fruits, which aid in dispersal and survival.
Q4. Explain the process of pollination and its types.
Answer: Pollination is the transfer of pollen from anther to stigma. It can be of two types: self-pollination, where pollen lands on the stigma of the same flower or plant, and cross-pollination, where pollen reaches a flower of a different plant. Pollination can be abiotic, by wind or water, or biotic, by insects, birds, or animals, helping in fertilization and seed formation.
Q5. Describe seed and fruit formation in flowering plants.
Answer: After fertilization, the zygote develops into an embryo inside the ovule, which matures into a seed. The ovary develops into a fruit that protects the seed and helps in its dispersal. Seeds can be dispersed by wind, water, or animals, reducing competition and increasing the chances of plant survival in new locations.
Conclusion
Sexual reproduction in flowering plants is a vital process that ensures species continuity, genetic diversity, and adaptation. From the structure of flowers to pollination, fertilization, and seed development, each step is intricately linked to create new life. Understanding this process not only provides insight into plant biology but also highlights the importance of reproduction in the survival of plant species.
Reproduction Class 12 Biology Notes | Complete Chapter with MCQs & FAQs
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