Lab 10 Embryonic Development

How many germ layers are present in the blastula of a sea star?

1 layer is present in the blastula

How many layers are present in the early gastrulation of a sea star?

2 layers are present in this stage

How many layers are present in late gastrulation of a sea star?

3 layers are present in this phase

What does it mean to be a deuterostome?

Animals in which the blastopore becomes the anus during early embryonic development

What type of yolk distribution are most likely to be found in human egg cells?

Considerable

What is a sign of early gastrulation?

Curvature of the blastula to form the blastopore.

What are the two major pathways of development?

Direct and metamorphic

What are blastomeres?

Early embryonic cells, enclosed in the zona pellucida of the zygote.

What is another name for zygote?

Fertilized egg

What is triploblastic?

Having a body derived from 3 embryonic cell layers and are in all multicellular animals except sponges and coelenterates

What axis does the neural groove form?

It forms the posterior-anterior axis.

What is the process of Frog Gastrulation

Slit-like blastopore forms on dorsal side at dorsal tip, extends around blastula, at the same time future endoderm and mesoderm expand by involution and shrinks blastocoel, at end blastopore surrounds yolk plug

What are the major events of fertilization?

The acrosomal reaction, the fast block to polyspermy, the cortical reaction, and the activation of the egg

What does it mean to be centrolecithal?

The amount of yolk present is considerable, the yolk is centrally located within thin layers, it has meroblastic cleavage, said cleavage has only the nuclei dividing in an early stage (coenocytically), its resulting blastomeres produce only a blastoderm (which is 1 layer around cell's periphery), and examples of this kind are fruit flies.

What is the difference between an ovum, morula, blastula, and gastrula?

The first is an unfertilized egg and is notably diploid and rigid in structure. The second is a tight collection of cells. The blastula is an early form of the organism as its cells start individual function. The gastrula has the thickest cell walls and begins the process of neurulation.

What are cleavages?

The initial cell divisions that produces a multi-celled embryo from the unicellular zygote

How do you structurally distinguish between a fertilized egg from an unfertilized egg?

The membrane is less cohesive in a fertilized egg

What is metamorphic development?

The process characterized by the presence of a larva and a completely transformative process that leaves the young of an organism radically different in appearance, structure, and even diet compared to its mature form.

What is the cortical reaction?

The sperm-egg fusion causes the release of calcium ions into the cytoplasm of the egg. This causes vesicles in the cortex to fuse with the plasma membrane. The cortical granules release enzymes into the perivitelline space and thereby allow it to become more fluid through the uptake of water. Such may elevate the vitelline layer where enzymes polymerize molecules to form a hardened fertilization membrane. This results in the slow-block to polyspermy because the fast-block has been negated.

What is the acrosomal reaction?

The vesicle of the sperm releases hydrolytic proteins that dissolve a pathway for the sperm through the jelly. Actin pushes through the jelly pathway until contact with the vitelline layer of the egg occurs. There's a specific adhesion protein that attaches to the vitelline layer,. The plasma membrane of the two gametes fuses and, finally, the sperm enters the cytoplasm of the egg.

What does it mean to be telolecithal?

There is a considerable amount of yolk, the yolk distribution is dense as it is concentrated at one end of the egg, it has meroblastic cleavage, said cleavage is restricted to a small disc at the end of the egg, its resulting blastomeres are smaller and more numerous around its animal pole than its vegetal pole, and examples of this kind are bird, reptile, and fish.

What does it mean to be mesolecithal?

There is an intermediate amount of yolk, said yolk distribution is concentrated around a vegetal pole, it has holoblastic cleavage, unequal and faster cleavage at the animal pole, smaller resulting blastomeres at animal pole, larger resulting blastomeres at vegetal pole, and an example of such is a frog.

What does it mean to be isolecithal?

There is little amount of yolk, the distribution of said yolk is uniform, it is holoblastic cleavage, rapid + equal throughout cleavages, smaller resulting blastomeres than the parent cell, and an example of such is a starfish.

Why is there a fast block to polyspermy?

This is because that it prevents more than one sperm from entering the egg at the time which could corrupt the fertilization process.

What is the activation of an egg?

This is the time wherein, at the time of fertilization, the pH within changes from 6.8 to 7.5. Then, the rate of protein synthesis expedites rapidly. Finally, after about 20 minutes, the sperm nucleus swells and merges with the egg nucleus to yield a diploid zygote. Finally, cell division occurs at about 90 minutes.

What is the endoderm and what will it form?

This layer is the innermost layer of the gastrula and will eventually become the absorptive lining of the gut (digestive tract), digestive glands, and lungs

What is the mesoderm and what will it form?

This layer is the middle layer of the gastrula and is only present in triploblastic organisms. It will eventually form the muscles, connective tissue, coelomic cavities, and kidneys.

What is the ectoderm and what will it form?

This layer is the outermost layer of the gastrula. It will eventually form the skin (epidermis) and nervous tissue, including the brain.

What are stages of development of a sea star in order?

Zygote -> early cleavage -> morula -> early blastula -> late blastula -> early gastrula -> late gastrula

What is a blastocyst?

a hollow ball of cells with a cluster of cells inside known as the inner cell mass

What is the amnion?

a thin but tough sac of membrane that covers an embryo; Main purpose is to protect the embryo during the months of pregnancy. It helps reduce the risk of injuries to the unborn embryo and its development in the womb.

What is a blastula?

an animal embryo at the early stage of development when it is a hollow ball of cells.

What is the trophoblast?

cells forming the outer layer of a blastocyst, which provide nutrients to the embryo and develop into a large part of the placenta

What is diploblastic?

having a body derived from only two embryonic cell layers (ectoderm and endoderm, but no mesoderm), as in sponges and coelenterates.

What is the allantois?

membrane sac that stores waste and is the site for gas exchange

What is the chorion?

outer membrane in extraembryonic membranes

What is the archenteron?

primitive gut formed during gastrulation; later, it forms the digestive system

What is neurulation and when does it occur?

process of folding which converts the neural plate to a hollow neural tube (which differentiates into the brain and spinal cord); 4th week

What is the vitelline membrane?

sack for the yolk, need this to keep the yolk in place, allows the whites and yolk to be separated

What is the blastocoel?

the fluid-filled cavity of a blastula

What is a blastopore?

the opening of the central cavity of an embryo in the early stage of development.

What is direct development?

there is no larval stage involved in development immature offspring is just a small version of the adult

What is a morula?

tight collection of 32 cells, beginning of differentiation