Answers and Solutions

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Becuse most of them died.

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Because the size of sperm are 10000 and more time smaller than egg. So to ensure fertilization they must produce in large no.

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Reason (1) 200-400 Million sperm produced from this amount only 60% sperm have normal shape and size and

from this only 40% have vigrous motility and contain more no of mitchondria as a energy source .

(2) Female genital tract is acidic in nature but acidic nature vary among diffrent women so acidic nature kill some sperm 

(3) Sperm have to travel against the gravity .

(4) Life of sperm within acidic environment in female genital tract is 24 hrs

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When sperms are released into the vagina near the cervix of the uterus, some semen backflow, while acidic pH of vaginal wall kills some sperms and many get trapped in mucus present near the cervix. Now only a few sperms swim to reach the oviducts, but the egg will be present inside only one of the oviducts. thus many sperms lose the chance of fertilizing the egg when they enter the wrong oviduct. so again only a few will try to reach the egg. it may take 2 hours to swim the distance to the egg. in the meantime only very active sperms go near the egg, while others die. As soon as one sperm enters the egg, the entry of the other sperms is prevented by a chemical barrier ie cortical reaction initiated by the cortical granules of the egg. ultimately we can say, 'survival of the fittest.'

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The entire saga of travel of sperm from testicle to ovum is a 2 1/2 hrs. journey in an inclement ambience. 200 to 480 millions of sperms starts the race from an alkaline environ to an acidic tunnel. A huge no, of sperms are killed by the acidic secretion and the trap of mucous in cervix.1 million reach the uterus. Within the cavity of uterus, sperms swim in congestion and about 12,000 succeeds to reach oviducts. Alas, only 1 oviduct contains the egg.There is no escape for sperms entered in empty oviduct. About 300 reach the fallopian tube only to swim for two more hours within the tube. Already exhausted, most of them either die or become useless. But robust few continues the journey to reach the ovum.But to penetrate the ovum they are to release hydrolysing enzymes to dissolve radiata and pellucida zones. Only one male gamete fertilises the female gamete to give birth to zygote. Thus, to increase the probability of producing a winner so many sacrificial sperms are required.

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Some Sperms die due to vaginal secretion.

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Because every sperm  motility,  development,  nuclear of sperm, and all part of sperm differently develop, then which sperm motility, speed, ability to fuse with ovum is more then all, that is the first sperm fused with ovum for fertilization, many sperm die in female reproductive track, and some have no ability to fuse with ovum , so thats why the large number of sperm produced  

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Fertilisation is the fusion of male and female gametes to give rise to a single cell – a zygote. b) Sperms are produced in large numbers to ensure the fertilisation of ovum. In the female reproductive tract, as sperms swim up to meet the ovum, *some sperms die due to vaginal secretions.