L4 Metazoan developement, body plans, lifecycles Flashcards
What is an isolethical ovum?
has a small amount of yolk within the cytoplasm, which his evenly distributed
What is a telolethical ovum?
Has its yolk concentrated toward the vegetal plate, amount varies greatly
What is a centerolethical ovum?
Yolk is concentrated at the centre of the cell, at the egg nucleus
Why are sea urchins used as an example of fertilisation?
Are in the same evolutionary line as the chordates
What is the acrosomal reaction?
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
What are bindin receptors?
very specific receptors on the egg membrane, which are very specific to the species
what is the fast block to polyspermy?
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
What is the slow block to polyspermy?
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.
What is the activation of the egg?
a change in the potential of the egg plasma
What is cleavage?
The rapid division of a newly fertilised embryo.
What type of cleavage do isolethical eggs undergo?
Holoblastic, complete cleavage, with little or no yolk present
What type of cleavage do telolethical eggs undergo?
mesoblastic, unequal cleavage, very yolky
What type of cleavage do centrolethical eggs undergo?
Superficial cleavage, central yolk mass
What are the twi patterns of cleavage?
Radial or spiral
What is gastrulation?
Proceeds cleavage. Cells of the vegetal regions gradually move inwards and a double walled cup is formed
What is the ectoderm?
External body cover, nervous system, sense organs
What is the endoderm?
Archenteron, gut, glands
What is the blastopore?
The opening of the archenteron in the gastrula
What is the blastocoel?
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
What is the archenteron?
The rudimentary alimentary cavity of an embryo at the gastrula stage.
What is the mesoderm?
gives rise to supportive tissues, muscles, lining of the body cavity
What is the difference in mesoderm formation in protostomes and deuterostomes?
mesoderm is formed by derivatives of the mesentoblast in the protostomes, and from archentric pinching in the deuterostomes
What are acelomates?
Lack a body cavity between the gut and outer body, mesoderm is a solid layer
What are pseudocelomates?
Body cavity is only partially lined by mesoderm, so isn’t a true coelom.
What are coelomates?
Body cavity lined entirely by mesoderm
What are the two evolutionary lineages of blastopore development?
Protostomes, mouth first, and deuterostomes, anus first
