Fertilization • Fertilization- results in a zygote • -requires the sperm & egg nucleus to fuse
Sperm Structure • Sperm- made of 3 parts • head- contains haploid nucleus & acrosome (enzymes that allow sperm to penetrate the egg) • middle piece- contains mitochondria (make energy; ATP) • tail- flagellum- allows sperm to swim toward the egg
Egg Structure • Egg structure contains 3 parts • -plasma membrane, vitelline envelope, jelly coat
Fertilization Process • Acrosome enzymes of sperm digest away the jelly coat • Acrosome extends a filament that attaches to a receptor on vitelline envelope (like a lock & key) • Nuclear membrane of sperm & plasma membrane of egg fuse
Fertilization Process (cont.) • Sperm nucleus enters the egg • Zygote forms when sperm nucleus & egg nucleus fuse • Following fusion, the egg plasma membrane & vitelline envelope undergo changes that prevent the entrance of other sperm • Vitelline envelope becomes the fertilization envelope
Fertilization Process • After egg is released from the ovary it moves into the fallopian tube and waits for the arrival of the sperm and fertilization to take place • Then wave-like action of cilia move the fertilized egg toward the uterus for implantation to take place
Development- all the changes that occur during the life of an organism • Embryo- 1st stages of development of an organism after the zygote forms
Cell Division1…2 buckle my shoe • Embryonic Development (Continued) • -zygote undergoes cleavage (cell division w/o growth)- mitosis and DNA replication occur repeatedly • Once the zygote is formed it begins to divide through a process called cleavage. • Upon completion of the first division, you have two cells. Then these two cells divide to form four cells.
Deuterostomes vs. ProtostomesSAY WHAT??? • 8-CELL STAGE IS KEY DIFFERENCE!!!-Deuterostomes- (starfish & vertebrates) cleavage results in 8 cells sitting directly on top of each other. This is called radial cleavage
Protostomes • protostomes (clams, worms, & insects) undergo spiral cleavage- cells divide and they do not sit on top of each other; they appear to spiral
Morula • The eight cells now continue to divide until you are simply a large solid ball of cells (16-32 cells). Morula
Blastula • At this time, the morula begins to form a hollow ball of cells called the blastula. • The blastula contains a fluid filled space known as the blastocoel.
Gastrula • Now gastrulation occurs. The hollow ball of cells known as the blastula begins to fold inward on one side • (imagine that you had a deflated basketball and pushed it in on one side). • When the folding occurs, it begins to create a horse shoe shaped structure that is 2 cell layers thick..
Gastrula (cont.) • The outer layer of the ball is called the ectoderm. The inner layer of the ball is called the endoderm. • Eventually, another cell layer will begin to form between the endoderm and ectoderm. This layer is called the mesoderm. • The point where the horse shoe almost touches is called the blastopore (small hole). • In protostomes this will eventually form the mouth. • In deuterostomes this will form the anus.
3 tissue layers • Ectoderm- forms nervous system & outer layer of skin • Mesoderm- forms muscle, bone, & cardiovascular system • Endoderm- organs of digestive system, lining of respiratory system & bladder