fertilization

purpose

to observe and identify stages of fertilization and different embryontic development of sea urchins

fertilization

fusion of a haploid sperm combining with a haploid egg creating a diploid zygote

what does sperm consist of

• head - that contains the nucleus

• acrosomes - release enzymes for sperm to penetrate the egg

• mitochondria - provides energy

• tail - helps with movement

egg structure

surrounded by a jelly coat that helps with protection and with fertilization

acrosomal reaction

sperm reaches the egg, acrosome releases enzymes that digest the jelly coat and allow sperm to reach the egg membrane

membrane fusion

egg and sperm membranes fuse, allowing the nucleus of the sperm to enter the egg

polyspermy

more than 1 sperm fertilizes to the same egg, leads to abnormal number of chromsomes

fast block

• happens immediately

• involves depolarization of the egg membrane due to sodium ion influx

• prevents more sperm from entering

slow block

-Calcium is released in an egg, causing corticle granules to release the fertilization envelope

fertilization envelope

formed when the viteline layer hardens and acts like a permanent barrier to prevent additional sperm from entering

calcium release

triggers a cortical reaction, activates the egg, allowing cell division to start

cleavage

series of mitotic devisions that divides zygote into blastomere without size increase

blastula

hollow ball of cells containing a fluid-filled cavity called a blastocoel

gastrulation

process in which blastula re-arranges to form the gastrula

archentenon

primitive gut

blastopore

opening for an anus

ecto, meso, endo layers + what they form

• ecto - outer layer, forms the skin and nervous system

• meso - middle layer and forms muscles and skeletons,

• end - inner layer and forms the digestive system