22.1 Fertilization and Early Stages of Development

Question 1

blastocoel

Answer 1

The blastocoel is the fluid-filled cavity inside a blastocyst (early-stage embryo). It forms during blastulation and helps create space for cell differentiation and future development of the embryo. The blastocoel plays a key role in implantation and the formation of germ layers during embryogenesis.

Question 2

blastula

Answer 2

The blastula is an early stage of embryonic development, consisting of a hollow ball of cells surrounding a fluid-filled cavity called the blastocoel. It forms after several rounds of cell division (cleavage) and precedes the gastrula stage, where cells begin to differentiate into distinct germ layers. In mammals, the blastula is called a blastocyst and plays a crucial role in implantation.

Question 3

cleavage

Answer 3

Cleavage is the rapid cell division of a fertilized egg (zygote) without an increase in overall size. It produces smaller cells called blastomeres and leads to the formation of a morula and then a blastula (or blastocyst in mammals). Cleavage is the first step in embryonic development, ensuring that the embryo has enough cells for differentiation and organ formation.

Question 4

corona radiata

Answer 4

The corona radiata is the outer layer of cells surrounding a secondary oocyte. It consists of follicular cells that provide nutrients and protection to the oocyte. During fertilization, sperm must penetrate the corona radiata and the zona pellucida to reach the egg.

Question 5

ectoderm

Answer 5

outer layer of cell