Explain fertilization with diagram
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Answer:
The fertilization process in animals can occur either internally or externally, a difference which is largely determined by the method of birth. Animals which use viviparous and ovoviviparous reproduction (embryos develop within the animal’s body), and oviparous animals which lay hard shelled eggs, use internal fertilization.
Internal fertilization involves the union of sperm and eggs within the body of the (usually female) parent. In order for internal fertilization to occur, the male must implant his sperm into the female reproductive tracts. Implantation can be achieved by either: copulation, in which sperm transfer is performed by insertion of the penis or other male intromittent organ and ejaculation into the vagina, or cloaca: or by a cloacal kiss, in which two birds press their cloacae together and sperm transfer takes place. Some animals, such as mollusks, arachnids, salamanders and certain insects, transfer a spermatophore, a bundle or capsule containing sperm, which is stored within the cloaca until oviposition takes place.
Animals which are oviparous, though produce eggs that are lacking, or have thin egg membranes, reproduce by external fertilization. External fertilization is a reproductive strategy involving the joining of gametes outside of the body, either in a spawning event, where gametes from both sexes are rapidly released into an aquatic environment, or may occur when eggs are laid by a female on a substrate, and are subsequently fertilized by a male. External fertilization holds certain benefits, such as reducing the chance of contracting sexually transmitted diseases, protection from violent behavior between organisms, and increasing the genetic variation within a population.
Fertilization in Plants
Fertilization in plants occurs after pollination and germination. Pollination occurs through the transfer of pollen – which is the male microgametes of seed plants, producing the sperm – from one plant to the stigma (the female reproductive organ) of another. The pollen grain takes up water and germination occurs.
The germinated pollen grain sprouts a pollen tube, which grows and penetrates the ovule (the egg structure of the plant) through a pore called a mycropyle. The sperm are then transferred through the pollen tube from the pollen.
In flowering plants, a secondary fertilization event takes place. Two sperm are transferred from each pollen grain, one of which fertilizes the egg cell to form a diploid zygote. The nucleus of the second sperm cell fuses with two haploid nuclei contained within a second female gamete called the central cell. This second fertilization forms a triploid cell, which subsequently swells and develops a fruiting body.
plant fertilization is the joining of male and female gametes, resulting in a zygote. The most generalized form of this process requires four steps: pollination, germination, penetration of the ovule, and fertilization. After fertilization, the zygote divides to form an embryo
