Reproduction In Animal Part-2 For Class 8th

Sexual Reproduction in Humans

  • In this method both male and female parents are involved.
  • Both have different reproductive systems.

The Male Reproductive System

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  1. Testes-
  • These are two in number
  • Somewhat Oval in Shape
  • They Lie within Scrotum
  • The Testes produce sperms in very large number

2. VAs Deferens (SpermDuct)-

  • This Duct starts from the testes and joins the urethra.
  • It Carries sperm to the urethra by the muscular action on its wall

3. Urethra

  • Vasdeferens carrying the sperm receives the fluid secreted by Seminal Vesicles.
  • This Provides nourishment to the sperms.
  • The Mixture of sperm and the fluid is called semen
  • This duct pens into the urethra

4. Penis

  • Urethra leads to a muscular organ called penis
  • it has erectile tissues and blood spaces which cause the stiffness of the penis.
  • it is used to pass urine as well as to deliver the male reproductive cells called sperms into the vagina of the female body.

Sexual Maturity in human males is attained around the age of 14-15 years, I.e. Male can produce sperms at this age.

The Female reproductive system

  1. Ovaries
  • There are two ovaries which are situated in the abdominal cavity. these produce one mature ovum each after every four weeks.

2. Oviduct- (Fallopian Tube)-

  • It is a thin coiled muscular tube which joins the uterus and the ovary.
  • it passes the ova into the uterus by its cilliary action

3. Uterus- It is a broader muscular chamber which receives the ovum and contains the developing foetus

4. vagina- The Uterus opens wide muscular tube called vagina.

Sexual Maturity in human female is attained at the age of 11-12 years.(at this age they start producing eggs(ovum).

Fertilization in Humans

  • The male produces millions of sperms in his testes each day.
  • a sperm is a single celled male gamete with three parts.
  • 1. A head with a nucleus, 2. A middle¬†piece 3. Long tail
  • The Sperms are mobile

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The Female Produces ova or eggs in her ovary

  • Each ovum is rounded structure ,of the size of a pin’s head.
  • it is many times larger than a sperm
  • One ovum or egg cell is released into the oviduct approximately in every 28 days.
  • The egg is also a single cell.

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Fertilization

  • The Fusion of egg with the sperm is called fertilization.
  • Fertilisation is internal as it takes place inside the females body in the oviduct.
  • During this process the nuclei of Sperm and Ovum fuse to form a single nucleus.
  • As a result the fertilized egg or zygote is formed.
  • Zygote is the beginning of new individual.

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Development of embryo

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  • The zygote formed after fertilisation begins to develop into an embryo.
  • it starts dividing repeatetly to produce a ball of cells
  • The developing structure is called embryo.
  • The embryo itself attaches to the wall of the uterus for further development.
  • Here it develops for the next nine months
  • The dveloping embryo gradually forms into different parts , such as hands,legs,head and other parts.
  • when the different body parts can be identified it is called a foetus.
  • At the time of birth the foetus weighs about 3 kg.

 

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In Vitro fertilization and test tube babies

  • In vitro certilization refers to the fusion of eggs with the spermsoutside the body of the female.
  • These kind of fertilization is undertaken in certain conditions where oviducts of women are blocked and therefore these women cant bear babies.
  • Sperms cant reach the egg for fertilization.
  • in such cases the freshly released ovum and so sperms are taken out and fused in a test tube.
  • in case the fertilization occurs,the zygote is further allowed to develop for about a week.
  • Then it is introduced inside the uterus of the mother.
  • Further development takes place in uterus like normal baby

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  • Babies born through the techniques of in vitro fertilization are called test tube babies.
  • Actually babies are not fully grown inside the test tube. only initial phase is done inside the tube.

The process of transformation of larva (or tadpole) into an adult through drastic changes is called metamorphosis.

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