Introduction to Sexual Reproduction in Plants
Definition of Sexual Reproduction
Sexual reproduction in plants is the process by which two parent plants contribute genetic material to produce genetically diverse offspring. It involves the fusion of male and female gametes (fertilization) and occurs primarily in flowering plants (angiosperms).
Significance of Sexual Reproduction in Plants
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Genetic Variation – Leads to evolution and adaptation in changing environments.
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Survival Advantage – Increases the ability of plants to resist diseases and environmental stress.
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Formation of Seeds – Ensures species continuity and dispersal through seeds.
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Improvement of Crops – Used in plant breeding to develop better-quality varieties.
Life Cycle of Angiosperms (Flowering Plants)
The life cycle of an angiosperm consists of alternation of generations, where haploid (n) and diploid (2n) phases alternate.
1. Sporophytic Stage (Diploid, 2n)
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The dominant phase in angiosperms.
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The mature plant produces flowers, which contain reproductive structures.
2. Gametophytic Stage (Haploid, n)
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Male gametophyte: Pollen grains (produced in anthers).
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Female gametophyte: Embryo sac (formed in ovule inside the ovary).
3. Pollination
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Transfer of pollen from anther to stigma (can be by wind, water, or animals).
4. Fertilization (Double Fertilization)
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One sperm fertilizes the egg → forms zygote (2n) → develops into an embryo.
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Other sperm fuses with polar nuclei → forms endosperm (3n, food source for embryo).
5. Seed and Fruit Formation
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Ovule develops into a seed.
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Ovary transforms into a fruit for seed dispersal.
6. Germination
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The seed germinates into a new sporophytic plant, completing the cycle.
Diagram: Life Cycle of an Angiosperm
(A labeled diagram illustrating stages from flowering, pollination, fertilization, seed and fruit formation, and germination.)
This life cycle ensures reproduction, genetic diversity, and survival of flowering plants across generations.