L4 Metazoan developement, body plans, lifecycles

Question 1

What is an isolethical ovum?

Answer 1

has a small amount of yolk within the cytoplasm, which his evenly distributed

Question 2

What is a telolethical ovum?

Answer 2

Has its yolk concentrated toward the vegetal plate, amount varies greatly

Question 3

What is a centerolethical ovum?

Answer 3

Yolk is concentrated at the centre of the cell, at the egg nucleus

Question 4

Why are sea urchins used as an example of fertilisation?

Answer 4

Are in the same evolutionary line as the chordates

Question 5

What is the acrosomal reaction?

Answer 5

occurs in the acrosome in the anterior of the sperm. When the sperm reaches the bona pellucid, the the acrosomal membrane fuses with the sperm head, exposing surface antigens that bind with the egg plasma membrane, and hydrolytic enzymes that break the membrane down for fertilisation to take place

Question 6

What are bindin receptors?

Answer 6

very specific receptors on the egg membrane, which are very specific to the species

Question 7

what is the fast block to polyspermy?

Answer 7

Immediately after the acrosomal reaction, plasma membrane of the egg depolarises, and na+ flows into the egg and the. charge of the membrane changes to be positive. This begins to triple any approaching sperm, which are positively charged

Question 8

What is the slow block to polyspermy?

Answer 8

The cortical reaction.C a + is released from the cytoplasm of the egg, which causes cortical granules to be released from around the edge and fuse with the plasma membrane. They contain enzymes that digest away the adhesion of the vitelline layer to the membrane - water is drawn into the space, and pushes layers further apart. The vitelline layer is polymerised.

Question 9

What is the activation of the egg?

Answer 9

a change in the potential of the egg plasma

Question 10

What is cleavage?

Answer 10

The rapid division of a newly fertilised embryo.

Question 11

What type of cleavage do isolethical eggs undergo?

Answer 11

Holoblastic, complete cleavage, with little or no yolk present

Question 12

What type of cleavage do telolethical eggs undergo?

Answer 12

mesoblastic, unequal cleavage, very yolky

Question 13

What type of cleavage do centrolethical eggs undergo?

Answer 13

Superficial cleavage, central yolk mass

Question 14

What are the twi patterns of cleavage?

Answer 14

Radial or spiral

Question 15

What is gastrulation?

Answer 15

Proceeds cleavage. Cells of the vegetal regions gradually move inwards and a double walled cup is formed

Question 16

What is the ectoderm?

Answer 16

External body cover, nervous system, sense organs

Question 17

What is the endoderm?

Answer 17

Archenteron, gut, glands

Question 18

What is the blastopore?

Answer 18

The opening of the archenteron in the gastrula

Question 19

What is the blastocoel?

Answer 19

a fluid-filled cavity that forms in the animal hemisphere of early amphibian and echinoderm embryos, or between the epiblast and hypoblast of avian, reptilian, and mammalian blastoderm-stage embryos

Question 20

What is the archenteron?

Answer 20

The rudimentary alimentary cavity of an embryo at the gastrula stage.

Question 21

What is the mesoderm?

Answer 21

gives rise to supportive tissues, muscles, lining of the body cavity

Question 22

What is the difference in mesoderm formation in protostomes and deuterostomes?

Answer 22

mesoderm is formed by derivatives of the mesentoblast in the protostomes, and from archentric pinching in the deuterostomes

Question 23

What are acelomates?

Answer 23

Lack a body cavity between the gut and outer body, mesoderm is a solid layer

Question 24

What are pseudocelomates?

Answer 24

Body cavity is only partially lined by mesoderm, so isn’t a true coelom.

Question 25

What are coelomates?

Answer 25

Body cavity lined entirely by mesoderm

Question 26

What are the two evolutionary lineages of blastopore development?

Answer 26

Protostomes, mouth first, and deuterostomes, anus first