03 April 2014

#125 Summary of Reproduction

Reproduction is the biological process by which new "offspring" individual organisms are produced from their "parents". It is a fundamental feature of all known life.
Two types of reproduction: sexual and asexual.

Asexual reproduction 

It involves cell division by mitosis, producing a group of genetically identical individuals called a clone. Bacteria, fungi and potatoes can reproduce asexually.

Sexual reproduction

Sexual reproduction involves the production of genetically different gametes by meiosis. A male gamete fertilises a female gamete, producing a zygote which is genetically different from its parents.

In human
  • The male gametes are sperms, they are made in the testes. During sexual intercourse, semen containing sperms passes out to the penis and into a woman’s vagina.
  • The female gametes are eggs and are made in the ovaries. After sexual intercourse, sperm swim through the cervix and uterus into the oviducts, where they may meet an egg. One sperm may fertilise the egg to produce a zygote.
  • The zygote travels to the uterus and implants into the lining, growing into an embryo attached t the uterus wall via an umbilical cord and placenta. The placenta brings the growing embryo’ blood very close to the mother’s blood, so that’s nutrients and waist products can diffuse between them.
  • The growing embryo is protected by amniotic fluid produced by the amnion.
  • After birth, a young mammal is fed on milk from its mother. This provides it with exactly the correct balance of nutrients, as well as antibodies which protect it from infectious diseases.
  • An egg is releases from an ovary about one a moth. If it is not feritlised, the thick lining of the uterus breaks down, in menstruation.
  • The menstrual cycle is controlled by the hormones oestrogen, progesterone, FSH and LH.
  • Birth control helps a couple t avoid having unwanted children. There are natural, surgical, mechanical and chemical methods.
  • Hormones can be used to increase fertility.
  • Gonorrhoea and HIV/AIDS are infectious diseases that can be transmitted by sexual contact.
In plants 

  • The flowers are the reproductive organs. Male gametes are make inside pollen grains, produced by anthers. Female gametes are make inside ovules produced by ovaries.
  • The movement of pollen from an anther to a stigma is called pollination, and may be brought about by insects of the wind.
  • After landing on a suitable stigma, a pollen grain germinates and the gametes travel down the style to the ovules. Here, fertilisation takes place and a zygote is produced. The zygote develops into an embryo, and the ovule develops into a seed. The ovary develops into the fruit, containing the seeds which contain the embryos.
  • Fruits are adapted to disperse seeds, using animals or the wind.
  • Seeds require certain condition before they will germinate.