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

Question 6

endoderm

Answer 6

inner layer of cell

Question 7

fertilization membrane

Answer 7

The fertilization membrane is a protective layer that forms around the egg after a sperm enters, preventing other sperm from getting in.

Question 8

gastrula

Answer 8

A gastrula is an early embryonic stage that forms after the blastula. It is when the three germ layers (ectoderm, mesoderm, and endoderm) develop, which later become different body tissues and organs.

Question 9

gastrulation

Answer 9

Gastrulation is the process in early embryo development where the blastula transforms into a gastrula, forming three germ layers: ectoderm, mesoderm, and endoderm. These layers give rise to all tissues and organs in the body.

Question 10

mesoderm

Answer 10

The mesoderm is the middle germ layer in an embryo that forms during gastrulation. It develops into the muscles, bones, blood vessels, heart, kidneys, and reproductive organs.

Question 11

morula

Answer 11

A morula is a solid ball of cells formed by the early cleavage of a zygote. It develops into a blastula and later implants in the uterus.

Question 12

zona pellucida

Answer 12

The zona pellucida is a protective glycoprotein layer surrounding the oocyte. It plays a key role in sperm binding, prevents polyspermy, and supports early embryo development until implantation.