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Explain the Terms Syngamy and Plastogamy. 



Syngamy is a fusion of the nuclei of two distinct indi- 

 viduals in reproduction. 



In the 'sexual union of a male with a female gamete 

 (sperm with ovum) there is fusion of cells as well as pro- 

 nuclei. In certain Protozoa there is fusion only of nuclei 

 or nuclear substance, which takes place after temporary 

 conjugation of the individuals. 



Plastogamy is not a reproductive process ; it is a union 

 of two or more individuals without fusion of nuclei. 



Plastogamic union may be temporary or permanent. 

 When permanent, the result is a composite of cell-indi- 

 viduals, a plasmodium. 



Define Sexual and Asexual Reproduction. 



In sexual reproduction, which is characteristic of Metazoa, 

 two dimorphic reproductive cells, the female ovum and 

 male spermatozoon, are liberated and unite. The result 

 of this union (syngamy) is fertilisation of the ovum by the 

 spermatozoon, involving amphimixis and followed by the de- 

 velopment of an individual from the fertilised egg or zygote. 



These sex cells are produced by two different individuals 

 (male and female), or by one individual either in different 

 organs (testis and ovary) or in one organ at different times 

 ( hermaphr oditism ) . 



Asexual reproduction is not preceded by conjugation. 

 It is a method of propagation by fission or by vegetative 

 budding (gemmation). The fission may be binary (as in 

 Amoeba) resulting in two individuals, or it may be multiple 

 (e.g., the spore formation known as schizogony in Sporozoa) 

 resulting in many. In Volvox it is multiple but restricted 

 to special cells of the colony called parthenogonidia. Bud- 

 ding occurs in Sponges, in Hydra (which liberates its 

 daughter- buds), and in Obelia and other hydroids which 

 form colonies by budding. 



Give the Meaning of the Terms Dichogamy and Amphimixis. 



Dichogamy is a form of hermaphroditism. Sperms and 



ova produced by the same animal but at different times. 



