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(a) Explain the process of double fertilization in angiosperms.

(b) Why does the development of endos[erm preceeds that of embryo?

(c) List the parts of a typical dicot embryo.

 

 

 

 
 
 
 
 

Answers (1)

(a)

  • After entering one of the synergids, the popllen tube release the two male gametes into the cytoplasm of the synergids.
  • One of the male gamete move towards the egg cell and fuses with its nucleus thus completing the syngamy. This results in the formation of diploid cell, the zygote.
  • The other male gamete moves towards the two polar nuclei loctaed in the central cell and fuses with them to form a triploid primary endosperm nucleus (PEN).
  • As this involves the fusion of these haploid nuclei it is termed as triple fusion.
  • Since two types of fusions, syngamy and triple fusion take place in an embryo sac, the phenomenon is double fertilization, an event unique to flowering plants.

 

(b) After triple fusion, the central cell becomes the primary endosperm cell (PEC) and develpos into endosperm while the zygote develops inta an embryo. The triploid endosperm tissue cells are filled with reserve food materials and are used for the nutrition of the developing embryo.

(c) 

  • A typical dicot embryo consists of an embryonal axis and two cotyledons.
  • The portion of embryonal axis above the level of cotyledons is the epicotyl which terminates with the plumule or stem tip.
  • The cylindrical portion below the level of cotyledons is hypocotyl that terminates at its lower end in the radicle or root tip. The root tip is covered with root cap .

Posted by

Priyanka Kumari

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