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CISCEISC (Science) ISC Class 12
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पाठ्यपुस्तक उत्तर९६७७
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अवधारणा स्पष्टीकरण और वीडियो५९६
समय सारणी१५
पाठ्यक्रम

Overview of Sexual Reproduction in Flowering Plants

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CISCE: Class 12

Definition: Double Fertilization

Fusion of one male gamete with the egg and the other with the polar nuclei in angiosperms is called double fertilization.

CISCE: Class 12

Key Points: Types of Endosperm in Angiosperms

Type of Endosperm Developmental Feature Occurrence Examples
Nuclear endosperm Initial divisions of primary endosperm nucleus without cell wall formation; walls form later or remain absent Most common type in angiosperms Cocos nucifera, sunflower, wheat, rice, maize
Cellular endosperm Cell wall formation starts from the first division; cells irregularly arranged Mostly in dicotyledonous families Petunia, Balsam, Datura
Helobial endosperm First division forms a transverse wall dividing embryo sac into two chambers, followed by free nuclear divisions Found in monocotyledonous plants Asphodelus
CISCE: Class 12

Definition: Embryogenesis

The process of development of mature embryo from diploid zygote is called embryogenesis.

CISCE: Class 12

Key Points: Development of Dicotyledonous Embryo

  • The first division of the zygote is transverse, forming a small apical cell and a larger basal cell.
  • The apical cell undergoes successive divisions to form the pro-embryo, passing through quadrant and octant stages.
  • The basal cell develops into a suspensor, which helps push the embryo into the endosperm; its upper cell forms the hypophysis that gives rise to the radicle.
  • The embryo passes through globular and heart-shaped stages, and differentiation of two cotyledons occurs.
  • The mature dicot embryo consists of two cotyledons and an embryonal axis differentiated into epicotyl, hypocotyl, plumule, and radicle.
 
CISCE: Class 12

Key Points: Development of Monocotyledonous Embryo

  • The zygote divides transversely into an apical cell and a basal cell, which further divide to form the pro-embryo.
  • Cells derived from the apical region form the single cotyledon and embryonal axis, while basal derivatives contribute to the root cap and periblem.
  • Monocot embryos possess one cotyledon, called the scutellum, positioned laterally on the embryonal axis.
  • The radicle and root cap are enclosed by coleorhiza, and the epicotyl with shoot apex is protected by coleoptile.
CISCE: Class 12

Definition: Parthenocarpy

The fruits which develop without fertilization are called parthenocarpic fruits and this phenomenon is described as parthenocarpy.

CISCE: Class 12

Definition: Polyembryony

The occurrence of more than one embryo in a single seed is called polyembryony.

 
CISCE: Class 12

Definition: Apomixis

The formation of seeds without meiosis and fertilization, where sexual reproduction is replaced by asexual methods, is called apomixis.

 
CISCE: Class 12

Key Points: Types of Apomixis

Type of Apomixis Characteristic Feature Origin of Embryo Examples
Non-recurrent apomixis Meiosis occurs; fertilization is absent From haploid egg or other embryo-sac cells Solanum, Nicotiana
Recurrent apomixis Meiosis absent; embryo sac is diploid From diploid embryo sac Taraxacum, Hieracium
Adventive apomixis (Adventive embryony) Embryo develops outside embryo sac From nucellus or integuments Citrus, Mangifera
CISCE: Class 12

Key Points: Formation of Seed and Fruit

  • After fertilization, the ovule develops into a seed, the integuments form the seed coat, and the endosperm may be absorbed or persist as food material.
  • The ovary develops into a fruit, and the ovary wall forms the pericarp, making the fruit a ripened ovary.
  • During seed formation, structures like synergids and antipodals degenerate, while the zygote forms the embryo and the secondary nucleus develops into endosperm.
CISCE: Class 12

Key Points: Types of Fruits

Type of Fruit Basis of Formation Key Feature Examples
True fruit Develops only from ovary Only ovary participates Mango, Guava, Grape
False fruit (Pseudocarp) Develops from ovary + other floral parts Thalamus or other parts involved Apple, Pear, Cashew
Parthenocarpic fruit Develops without fertilization Seedless fruit Banana
Drupe Fleshy fruit with hard endocarp Mesocarp fibrous or fleshy Coconut, Mango
CISCE: Class 12

Key Points: The Seed

  • In angiosperms, a seed is a mature fertilized ovule containing an embryo, stored food, and a protective seed coat.
  • After fertilization, the zygote forms the embryo, the endosperm nucleus forms endosperm, and integuments develop into seed coats.
  • Seeds show great variation in size, shape, and structure, and may bear special features like hilum, funicle, and aril.
  • Seeds ensure plant survival and dispersal, provide genetic variation, and are a major source of human food and agricultural products.
CISCE: Class 12

Key Points: Classification of Seeds

A. Based on Number of Cotyledons

Type of Seed Cotyledons Examples
Dicotyledonous seeds Two cotyledons Gram, pea, bean, castor
Monocotyledonous seeds One cotyledon Rice, maize

B. Based on Presence or Absence of Endosperm

Seed Type Endosperm Characteristics Examples
Albuminous (Endospermic) Present Endosperm nourishes embryo Castor, cereals, maize
Exalbuminous (Non-endospermic) Absent at maturity Cotyledons store food Pea, bean, groundnut
CISCE: Class 12

Key Points: Structure of Common Seeds

Feature Dicotyledonous Exalbuminous Seed (Bean) Monocotyledonous Albuminous Seed (Maize)
Seed coat Hard seed coat with testa and tegmen Seed coat fused with pericarp
Cotyledons Two fleshy cotyledons One cotyledon (scutellum)
Endosperm Absent; food stored in cotyledons Present; stores starch
Embryo parts Radicle, plumule, hypocotyl, epicotyl Radicle and plumule present
Special structures Hilum, micropyle, raphe present Coleoptile and coleorhiza present
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