याद रखने योग्य अवधारणाएँ और फॉर्मूला
Fertilization in Flowering Plants:
- Unique and essential process in angiosperms.
- Involves fusion of male and female gametes, forming a zygote and endosperm.
- Begins with pollination and ends with seed development and fruit formation.
Entry of Pollen Tube into Ovule:
- Critical step in fertilization.
- Pollen germination and tube growth.
- Micropyle entry, penetration, and guidance by synergid cells.
- Leads to egg cell and central cell fertilization.
Double Fertilization:
- Unique to angiosperms.
- Two sperm cells from pollen fuse with different female gametophyte cells.
- Forms a diploid zygote and triploid endosperm.
- Essential for seed development.
Development of the Endosperm:
- Nourishing tissue for embryo.
- Originates from the triploid nucleus.
- Involves mitotic divisions, cellularization, and nutrient accumulation.
- Functions as a nutrient reserve for embryo growth.
Stages in Cellular Endosperm Development:
- Initiation of endosperm with a triploid nucleus.
- Mitotic divisions leading to syncytium.
- Cellularization forming individual cells.
- Cell expansion, nutrient accumulation, and maturation.
- Nutrient reservoir for embryo.
Stages in Helobial Endosperm Development:
- Triploid primary endosperm nucleus formation.
- Free nuclear divisions, forming a coenocyte.
- Cell wall formation within the coenocyte.
- Cell expansion, nutrient accumulation, and maturation.
- Nutrient reservoir for embryo.
- Fate of helobial endosperm varies among grass species.
Steps in development of Embryo in Dicot Plants:
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Fertilization: It begins with the fusion of sperm and egg cells, forming a diploid zygote and initiating embryo development.
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Zygote Division: The zygote divides into the terminal cell (forms most of the embryo) and the basal cell (involved in suspensor formation).
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Suspensor Formation: The suspensor connects the embryo to maternal tissues, aiding nutrient uptake.
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Embryo Proper: It includes the radicle (embryonic root), hypocotyl, cotyledons (usually two), and plumule (embryonic shoot).
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Storage Reserves: Nutrient storage occurs in cotyledons or other regions, supporting seedling growth.
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Maturation: Prepares the embryo for dormancy inside the seed.
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Seed Coat Formation: Provides protection to the embryo.
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Dormancy: Many dicots enter dormancy within the seed until suitable germination conditions.
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Germination: Resumption of growth under favorable conditions.
Steps in development of Embryo in Monocot Plants:
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Fertilization: Same as dicots, forming a zygote and initiating embryo development.
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Zygote Division: Divides into apical cell (forms most of the embryo) and basal cell (involved in suspensor).
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Suspensor Formation: Multicellular suspensor connects embryo to maternal tissues.
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Embryo Proper: Includes radicle, cotyledon(s) (usually one), and plumule.
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Storage Reserves: Nutrients accumulate in cotyledon(s) or other regions.
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Maturation: Prepares the embryo for dormancy.
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Seed Coat Formation: Protects the embryo.
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Dormancy: Enter dormancy within the seed.
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Germination: Resumption of growth under favorable conditions.
Steps in development of Seed:
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Fertilization: Begins with pollination and double fertilization, forming a seed.
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Ovary Enlargement: The ovary grows and develops into the fruit.
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Seed Development: The embryo and endosperm (if present) develop within the ovule.
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Pericarp Development: The fruit’s ovary wall undergoes changes.
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Fruit Growth: The fruit enlarges as cells divide or expand.
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Fruit Ripening: Complex biochemical changes alter color, texture, and flavor.
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Dispersal: Mechanisms (wind, animals, water) distribute mature seeds.
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Germination: Seeds sprout when conditions are favorable.
Steps in seed Germination:
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Imbibition: Seeds absorb water, activating enzymes.
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Activation of Enzymes: Water activates enzymes that break down stored nutrients.
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Radicle Emergence: The embryonic root emerges first, followed by the shoot.
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Growth of Plumule: The shoot elongates and develops into leaves and stems.
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Cotyledon Function: In dicots, cotyledons provide nutrients until photosynthesis begins.
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Photosynthesis: Seedling becomes self-sufficient through photosynthesis.
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Establishment: Seedling grows into a mature plant.
Steps in development of Fruits:
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Fertilization: Fruit development starts with ovule fertilization.
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Ovary Enlargement: The ovary grows and becomes the fruit.
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Seed Development: Embryo and endosperm form within the ovule.
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Pericarp Development: The fruit’s ovary wall changes.
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Fruit Growth: The fruit enlarges due to cell division or expansion.
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Fruit Ripening: Biochemical changes alter color, texture, and flavor, attracting animals.
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Dehiscence or Indehiscence: Fruits may split open or remain closed at maturity.
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Seed Dispersal: Various mechanisms disperse seeds (wind, animals, water).
Apomixis:
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Asexual Reproduction: Seeds produced without fertilization, resulting in genetic clones.
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Types of Apomixis: Agamospermy, apospory, and parthenogenesis are different forms.
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Clonal Offspring: Offspring are genetically identical to the parent plant.
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Reproductive Advantages: Apomixis can be advantageous in specific environments.
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Common in Some Plant Families: Found in grasses, dandelions, and certain citrus species.
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Applications in Agriculture: Studied for crop improvement and genetic stability.
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Seed Production: Apomixis allows for predictable seed production.
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Genetic Diversity: Apomixis does not contribute to genetic diversity.