11.2.3 Fertilization

Process of Fertilization

• Pollen tube growth: After pollination, the mature pollen grain lands on the stigma of the carpel. The pollen tube grows, penetrating the style and absorbing nutrients from the surrounding liquid.

• Male gametes in the embryo sac: Once the pollen tube reaches the ovule in the embryo sac, it releases two male gametes.

• First male gamete: Fuses with the egg cell, forming a zygote.

• Second male gamete: Fuses with the two secondary nuclei, forming the triploid endosperm (3n).

• This simultaneous fusion of two male gametes is called double fertilization.

Development of the New Sporophyte

• The zygote is the first cell of the new sporophyte. It divides, producing two cells:

• The basal cell (towards the micropyle) and the apical cell (towards the center of the embryo sac).

• The apical cell develops into the embryo.

• Endosperm formation: The secondary nuclei develop into the endosperm, which nourishes the growing embryo. The endosperm cells are triploid (3n), meaning they have three sets of chromosomes.

• The development continues:

• Cotyledons, radicle, and plumule form sequentially.

• The embryo and endosperm mature to form the seed.

• As the seed germinates, a new sporophyte is produced.

Structure of Ovule and Fertilization

The ovule contains several key parts involved in fertilization:

• Male gametes: From the pollen grain.

• Egg cell: Where one male gamete fuses to form the zygote.

• Secondary nucleus: Where the second male gamete fuses to form the endosperm.

Origin of Fruits

• Fertilization initiates fruit development: After fertilization, the ovary undergoes stimulation and turns into the fruit, while the ovules inside become seeds.

• True fruits: If only the ovary develops into the fruit, it is a true fruit. Examples: Mango, berries.

• False fruits: If other parts of the flower, in addition to the ovary, mature into the fruit, it is a false fruit. Examples: Apple, Elephant Apple (Chalita).

Categories of Fruits

1. Fleshy fruits

2. Aggregate fruits

3. Compound fruits

These fruits can either be true or false, depending on the involvement of the flower’s other parts in fruit formation.