Hi class,
Here are the links.
Brain Pop - Fertilisation and Birth
From Egg to Embryo
Development of the foetus month by month
Do also spend some time to think about the questions which your classmates have asked.
1) Do sperms have 'eyes' to find their way around?
2) Can sperms smell?
3) What is a placenta?
4) Why are there millions of sperms when only one can fertilise the egg?
Have a nice weekend. Study hard!
No sperm do not have eyes. But...
ReplyDeleteScientists often pondered the amazing navigation that these apparently primitive bundles of cells have at finding their way to the egg, and for a long time it appeared that the navigation was done using chemical signals.
But it appears that the human sperm cell is in fact extremely sophisticated.
Not only can they travel distances which scaled up represents a human walking thousands of miles but they even "dock" with the lining of the womb to take on fuel for the journey. According to recent research done by the Weizmann Institute human sperm finds it way to the zygote (female egg), by using heat sensors.
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and lizards with varying levels of development up to mammalian levels.[1] Native Hawaiians believe that the placenta is a part of the baby, and traditionally plant it with a tree that can then grow alongside the child.[17] Various cultures in Indonesia, such as Javanese, believe that the placenta has a spirit and needs to be buried outside the family house.
ReplyDeleteOnce the first sperm penetrates the egg, a series of changes take place in the protective layers around the outside of the main part of the egg (oocyte). This process, called the cortical reaction, makes the layers hard and not able to be penetrated by any other sperm.
ReplyDeleteAlso I'd like to add..... When the sperm's plasma membrane fuses with the egg's plasma membrane, there is a depolarisation of the egg's plasma membrane caused by an influx of sodium ions into the cell. This acts as a temperary barrier (several minutes) to other sperm until the outer vitiline layer of the egg becomes solid!!