proses pembuahan

Pembuahan atau fertilisasi (singami) adalah peleburan dua gamet yang dapat berupa nukleus atau sel-sel bernukleus untuk membentuk sel tunggal (zigot) atau peleburan nukleus. Biasanya melibatkan penggabungan sitoplasma (plasmogami) dan penyatuan bahan nukleus (kariogami). Dengan meiosis, zigot itu membentuk ciri fundamental dari kebanyakan siklus seksual eukariota, dan pada dasarnya gamet-gamet yang melebur adalah haploid. Bilamana keduanya motil seperti pada tumbuhan, maka fertilisasi itu disebut isogami, bilamana berbeda dalam ukuran tetapi serupa dalam bentuk maka disebut anisogami, bila satu tidak motil (dan biasanya lebih besar) dinamakan oogami. Hal ini merupakan cara khas pada beberapa tumbuhan, hewan, dan sebagian besar jamur. Pada sebagian gimnofita dan semua antofita, gametnya tidak berflagel, dan polen tube terlibat dalam proses fertilisasi.

Fertilisasi pada hewan
Fertilisasi eksternal (khas pada hewan-hewan akuatik): gamet-gametnya dikeluarkan dari dalam tubuhnya sebelum fertilisasi.
Fertilisasi internal (khas untuk adaptasi dengan kehidupan di darat): sperma dimasukkan ke dalam daerah reproduksi betina yang kemudian disusul dengan fertilisasi. Setelah pembuahan, telur itu membentuk membran fertilisasi untuk merintangi pemasukan sperma lebih lanjut. Kadang-kadang sperma itu diperlukan hanya untuk mengaktivasi telur.

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2 responses to “proses pembuahan”

  1. RIFATUL MAHMUDAH says :

    ad proses fertilisasai ?>

    • rian135 says :

      ni contohnyaa:

      The baby in your arms is now the star of your life. But how does the baby in your arms actually form into a human baby. Its the process of fertilization from where it begins. Before ovulation, mucus is secreted which is extremely stretchable. This is the highly fertile period for chancing conception. As it is the mucus that carries the sperm into the uterus.

      During intercourse the excitement dilates the arterioles that supplies the blood to the penis. The blood then is accumulated in three cylindrical soft sinuses that move through the penis lengthwise. They cause pressure that enables the penis to enlarge, get erect and penetrate the vagina.

      Straddling increases the tension to end in ejaculation where the walls of the vas deferns contract and force the sperm out. On the way out seminal vesicles, Cowper’s glands, and the prostate glands add some more fluids. These fluids are like a source of energy they provide a chemical environment for the sperm. When the sperm is mixes with these fluids it is called semen. It helps the mobility of the sperm into the urethra and to the vagina.

      From the vagina the sperm moves on to the egg i.e. through the fallopian tubes to the egg (i.e. if the egg is present). The sperm swims for several centimetres every second but the muscular movement of the wall of the uterus and the tubes helps its mobility. Research also claims that the egg attracts the sperm through some chemical secretions.

      However, the sperm takes at least 15 minutes to reach the egg. At any ejaculation a hundred thousand sperms are flushed out. Out of these only a few reach the urethra and only one breaks the egg.

      When the sperm reaches the egg, fertilisation begins. First the head of the sperm gets attached to the egg. As they merge the concerned membranes take in all the contents of the sperm into the egg. Immediately the egg releases the cytosol from the egg that makes it impenetrable for the other sperms that arrive.

      Then the nucleus of male increases in size to form the male pronucleus and the egg enlarges to form the female pronucleus. These two nuclei then move to form a set of chromosomes, this them is the fertilized egg or zygote.

      The zygote then gets settled in the womb and sends the message to the brain that fertilization has taken place. The body then gets ready to house a baby.

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