Question

Explain double fertilization and trace the post fertilization events in sequential order leading to seed formation in a typical dicot plant

Answer 1

pollen grain contain two male gemetes one fuses with egg and another fuses with central cell to form primary endosperm nucleus , the whole process is known as doible fertilisation.
after double fertilisation primary enfosperm nucleus is converted inro primary endosperm cell which is ised as food for developing seed.

Answer 2

(a) As a result of pollen-pistil interaction, germination of pollen tube takes’ place carrying two male gametes. One male gamete fuses with the egg cell (syngamy), while the other fuses with two polar nuclei to form primary endosperm nucleus (PEN). The zygote develops into an embryo while the PEN develops to form endosperm. After double fertilisation, the ovule matures into a seed while the ovary matures into a fruit.

(b) Different types of pollination depending upon the source of pollen grain are :

Autogamy: Transfer of pollen grains from the anther to the stigma of the same flower. Geitonogamy : Transfer of pollen grain from the anther to the stigma of another flower of the same plant. Xenogamy : Only types of pollination which brings genetically different types of pollen grains .

OR

(a) Fertilization : A sperm comes in contact with the zona pellucida layer ovum and induces changes to block entry of additional sperms. The entry of sperm induces completion of meiosis II leading to the formation of anootid and second polar body. The haploid nucleus of the sperm and that of the ovum fuse to form a dipolid zygote.

Implantation : The trophoblast layer of the blastocyst attaches to the endometrium of the uterus. The uterine

cells divide rapidly and cover the blastocyst which becomes embedded in the endometrium and implantation is completed.

(b) Placenta acts as an endocrine tissue and produces several hormones like :

human chorionic gonadotropin (hCG) human placental lactogen (hPL) Estrogens, progestogens, etc.

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