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Gametogenesis And Oogenesis ! Process, Mechanism, Stages !! Biological Sciencess !!!

GAMETOGENESIS The process of formation off gametes in the gonads is called gametogenesis. Gametes are produced by way of meiotic division resulting in the reduction of number of chromosomes to one half. The production of sperms in the seminiferous tubules of testis is called spermatogenesis and production of ova in ovaries is called oogenesis. 1. Spermatogenesis Spermatogenesis is the process of formation of haploid functional spermatozoa from diploid germinal cells of seminiferous tubules. Lining layer of seminiferous tubules possesses primary germ cells and indifferent cells that mature into nurse cells or Sertoli cells. (i) Multiplication Phase Diploid primary germ cells undergo repeated mitosis to form a number of diploid spermatogonia. (ii) Spermatocytogenesis Each spermatogonia divided mitotically to from two interconnected primary spermatocyte (iii) Growth Phase Primary spermatocytes grow in size. (iv) Maturation Phase Each diploid primary spermatocyte

Top 6 Main Types of Natural Habitats ! Total Information !! Biological Sciencess !!!

Top 6 Main Types of Natural Habitats Apart from the biogeographic classifications described above ecosystems can also be demarcated on the basis of purely geographical or geological features like mountains, islands, valleys, plateaux, oceans; on the basis of vegetative cover like forests, grasslands, mangroves and deserts; on the basis of climatic conditions like arid and semi-arid areas, permanently snow-bound areas, high rainfall areas; on the basis of soil characteristic and other such criteria. In some descriptions the biomes/ecosystems are clubbed together into very general habitat classifications. The main natural habitat types are 1. Forests The forest cover of the country is placed at 633 397 sq km according to the forest survey of India assessment (1997). This presents 19.27% of India’s total geographical areas. India is endowed with diverse forest types ranging from the Tropical wet evergreen forests in North-Eastern to the Tropical thorn forests in

Mechanism Of FERTILIZATION IN HUMANS ! Biological Sciencess !!

FERTILIZATION IN HUMANS Only a single ovum is released in human females from one of the two ovaries towards the middle of ovarian/menstrual cycle. It passes into fallopian tube and rests inside ampulla for some time. Human male produces 300 - 400 million sperms per ejaculation. They are deposited in vagina during coitus. The process of deposition of sperms in the female genital tract is called insemination. A number of them are demobilised or eaten. Fertilization involves the following steps (i) Approximation of Sperm and Ovum. Sperms can remain motile for 24-48 hours. They swim at the rate of 1. 5 - 3.0 mm/min. They are able to reach the ampulla part of female genital tract partly by their own swimming and partly by contraction of uterus and fallopian tubes. One sperm comes to lie against the ovum and undergo fertilizin (from ovum) and antifertilizin (from sperm) compatibility reaction (Lillie, 1919) in the region of animal pole. (ii) Acrosome Reaction. It prepares

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