Embryonic Development

Front 1

Triploblastic (define)

Back 1

Having three tissue layers

Front 2

What phyla are not triploblastic?

Back 2

Porifera (Sponges) and Cnidaria (Jellyfish)

Front 3

Name the stages of embryonic development in order from first to last. (6)

Back 3

1.) Fertilization
2.) Cleavage stage
3.) Morula
4.) Blastula
5.) Gastula
6.) Neurula ( only occurs in chordates.)

Front 4

Fertilization (define)

Back 4

The union of an egg and sperm nucleus resulting in a diploid zygote.

Front 5

what occurs after fertilization (not the stage following)?

Back 5

The zygote will begin to divide by mitosis and cytokinesis. In humans it is about 36 hours after fertilization before the zygote divides into new cells.

Front 6

Cleavage stage (define and explain)

Back 6

Rapid cell division with no time for cell growth between divisions is occurring.

The embryo does not gain in total size but there is an increase in the number of cells.

Front 7

What are the two basic patterns of cleavage?

Back 7

Radial and Spiral

Front 8

How are these patterns different and which do humans divide by?

Back 8

spiral-the fate of each cell is determined from the moment it is formed.

In animals with spiral cleavage if one cell splits off from the mass both parts will fail to develop.

In humans and other animals with radial cleavage the fate of a cell is not determined at the moment it is formed.

Any cell can become any structure.

If one cell seperates from the rest of the embryo identical twins will develop.

Front 9

Morula Stage (define and explain)

Back 9

Occurs at over 100 cells in humans.

Around day 5

Identical twins can still form.

Front 10

Blastula stage (define and explain)

Back 10

Cells migrate outward and the embryo becomes a sphere with one layer of cells surrounding a central fluid filled cavity.

Each cell is known as a blastomere.

The cavity is a blastocoel.

Identical twins can still develop in species with radial cleavage.

Front 11

Gastrula Stage (define and Explain)

Back 11

1.) Stage in which differentiation occurs.
2.)Begins around the 14th day post fertilization.
3.) At one pole of the blastula cells migrate inward.
4.) as the cells move, their position will determine what structure they will become.
5.) No longer can cells become any structure.
6.) Identical twins can no longer form.
7.) Archenteron develops and this cavity becomes the GI tract. The opening into it is the blastopore. In humans the blastopore becomes the anus and the mouth develops later.
8.) The three tissue layers formed are the endoderm, ectoderm, and mesoderm.

Front 12

How are triploblastic animals classified?

Back 12

Based on what the blastopore becomes. If it becomes the anus a deuterostome will develop . If it becomes the mouth a protostome will form.

Front 13

What are the two phyla formed from deuterostomes?

Back 13

Echinodermata (starfish, sea urchins, sand dollars)

Chordata (Fish, amphibians, reptiles, birds, mammals)

All other phyla are protostomes.

Front 14

Neurula Stage (Define and Explain)

Back 14

Occurs in chordates. Stage in which the nervous system begins to develop.

The development of the Notocord occurs on day 17 in humans.

Arises from the mesoderm.

It stimulates the formation of the neural plate from the ectoderm.

The neural plate becomes a neural groove then a nerual tube along the dorsal surface of the embryo.

The anterior end of the tube enlarges to become the brain.

The posterior end becomes the spinal cord.

Front 15

What is left by the degeneration of the notochord?

Back 15

The nucleus pulposus, a mass of jellylike material in the center of each intervertebral disc.