Echinoderm Fertilization (LP.2)

Question 1

What are the 3 key events?

Answer 1

• Fertilization (creation of diploid zygote)
• Cell Division
• Cell movements (move inside embryo)

Question 2

When does development begin for many animals & some plants?

Answer 2

-BEFORE FERTILIZATION= Oogenesis (egg production)

Question 3

What 2 things does fertilization accomplish?

Answer 3

• Activates oocyte (egg) to complete its development

- Helps haploids from both parents to become diploid to then create a zygote

Question 4

What is the first thing that happens in Sea Urchin fertilization?

Answer 4

-The Fertilization membrane lifts off the surface of the egg once the first sperm makes contact w/ it

Question 5

What is the role of the Fertilization Membrane?

Answer 5

-To prevent Polyspermy (more than one sperm entering egg)= ensures the zygote will be diploid

Question 6

What was the purpose of this lab?

Answer 6

-To see the stages of development of a sea star

Question 7

How was gamete shredding induced?

Answer 7

-Via injecting the urchins with .53 M KCL

Question 8

At what objective did we observe the eggs under?

Answer 8

10x

Question 9

What occurs once the Fertilization Membrane begins to blister?

Answer 9

• It marks the beginning of it encompassing the whole egg

- The male pronucleus migrates towards the female pronucleus while the tail of the sperm (flagella) is left outside

Question 10

What is the cleavage of sea urchin like?

Answer 10

-They’re Holoblastic= they cut through the entire embryo vertically (animal pole to vegetal pole) & results in 2 blastomeres

Question 11

What kind of environment do Echinoderms develop from?

Answer 11

-From eggs with little or no yolk

Question 12

What is a key characteristic of the eggs?

Answer 12

-They have polarity

Question 13

What is the nucleus like in an Echinoderm egg?

Answer 13

-It is offset towards Animal pole (Top of the egg)

Question 14

Where is the Vegetal Pole located on an egg?

Answer 14

-At the bottom

Question 15

What is the 2nd cleavage like?

Answer 15

-It is also verticle but at a right angle to the first cleavage= results in 4 blastomeres

Question 16

What is the 3rd cleavage like?

Answer 16

-Horizontal which cuts the 4 blastomeres into 8 blastomeres, then these blastomeres further divide to create the Morula

Question 17

What is the difference between Cell Division and Cleavage?

Answer 17

-There is no cell growth when in cleavage= cell size decreases as the cleavage continues

Question 18

What is a Blastocoel?

Answer 18

-The balls of cells that are in the cleavage process forming a cavity in the middle

Question 19

What happens during Gastrulation?

Answer 19

• The cells at the vegetal plate= Primary Mesenchyme cells detach & migrate within the embryo
• Then the vegetal plate buckles inward to form the endoderm= makes archenteron (primitive gut)

Question 20

What are Primary Mesenchyme cells?

Answer 20

-They are Mesoderm cells used in gastrulation to form the skeleton of the larvae that develops

Question 21

Where is the Ectoderm located within all this process?

Answer 21

-It is left outside to develop into the outer regions of the larvae

Question 22

What happens when the Archenteron is makin’ its way up inside the embryo?

Answer 22

-It makes contact w/ the sidewall of the gastrula & then breaks through that point to form the Oral Opening

Question 23

What is the Blastopore?

Answer 23

-The original opening of the gastrula which then becomes the anus of the larvae

Question 24

What family do Echinoderms belong to?

Answer 24

-Deutrosomes

Question 25

What is the overall process then?

Answer 25

Zygote–>Cleavage+ more Cleavage–>Morula (16) –>Cleavage–>Blastula–>Early Gastrula–>Late Gastrula

Question 26

What is a Morula?

Answer 26

-Compact mass of embryonic cells

Question 27

What is a Blastula & what is the name of the cells surrounding it?

Answer 27

• Hollow ball of cells (has the cavity in the middle)

- The wall of cells around the cavity= Blastoderms

Question 28

What is the cavity in the middle of a Blastula called?

Answer 28

-Blastocoel= has fluid

Question 29

What is the difference between an Oocyte and an Egg?

Answer 29

-An oocyte hasn’t finished meiosis