Fertilization is done by germination of pollen on the pistil, without need of moisture as in the case of ferns (character they share with other Spermaphytes).
In Angiosperms fertilization has three essential characteristics:
* it is siphonogamous: the apertured pollen grain possessing two or three cells sees its vegetative cell germinate and form a pollen tube which will convey, with the help of its cytoskeleton, the male gamete (case of the tricellular pollen) where the generating cell ( case of the bicellular pollen) which will carry out its second division of meiosis. In this siphonogamy corresponds to a total franking of water for fertilization.
* it is anisogamous: the female gamete is by far the most massive of the two (the pollen grain is often very dehydrated, the cells it contains have a very small cytoplasmic space).
* it is double: the male gametes conveyed by the pollen grain will merge their nuclei (caryomixis) with those of two different cells. It's a special function for the reproduction of angiosperms. The pollen grain contains two nuclei (all haploids), whereas for example the mammalian spermatozoa contains only one.
its answer is A.
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Red blood cells transport oxygen throughout the body platelets aid in blood clotting and white blood cells help destroy and remove old cells and foreign substances. This is an example of how cells origin from the same cell (hematopoietic cell in the bone marrow) and then differentiate.
Hematopoietic stem cells are blood-forming stem cells. During hematopoiesis the hematopoietic stem cell divides via mitosis. As a result of mitosis, one daughter cell remains in the bone marrow to continue renewing the hematopoietic stem cells pool while the other goes through next stages of development. Maturate blood cell (red, white or platelet) to leave the bone marrow and enters the circulation.
