1. What were two ideas about development that were prevalent before the 19th century?

 Preformation was the idea that a little tiny human was carried by the sperm. Epigenesis (our current view) is the idea that development occurred from a formless egg. It was originally proposed by Aristotle.

2. What occurs during mitotic cell division, differentiation, and morphogenesis?

 Cell division makes more cells identical to the first. Differentiation is the process by which cells specialize to perform different functions. Morphogenesis is the process by which the embryo takes on its form.

3. Define cleavage, blastula, blastopore, blastocoel. What are two consequences of cleavage?

 Cleavages are the early cell divisions that form a solid ball of cells (the morula). When this ball becomes hollow it is a blastula and the cavity inside is the blastocoel. When gastrulation happens in a sea urchin, the spot at which invagination occurs is called the blastopore.

Cleavage results in more cells, but these cells are smaller than the original zygote. So the cells are more numerous and smaller.

4. Define gastrulation and the primary germ layers that result from this process. What are some tissues or organs are the primary germ layers fated to form?

 Gastrulation is the process of invagination that forms the three embryonic tissue layers: ectoderm, mesoderm, and endoderm. The ectoderm will form skin and nervous system; the mesoderm will form bones, muscle; the endoderm will form the lining of the digestive tract and associated organs (liver, pancreas) as well as the lungs.

5. What is the archenteron? What does it form in the embryo?

 The archenteron is the cavity that forms as a result of gastrulation. It will become the digestive tract with the mouth at one end and the anus at the other.

6. A group of cells begin producing keratin, a protein found in skin cells. These cells have just undergone differentiation / morphogenesis. Which embryonic tissue layer did these cells come from?

 Ectoderm

7. Drosophila (fruit fly) zygotes undergo several rounds of mitosis without cytokinesis. After 5 rounds of mitosis, how many cells would the embryo have? How many nuclei?

 1 cell with 32 nuclei

8. Suppose you placed a zygote in a chemical that inhibited whole cell movement but not organelle movement. Would this chemical affect:

Cleavage divisions? No 

Gastrulation? Yes. Cells must migrate from their original positions to new positions during gastrulation. 

Morphogenesis? Yes. Part of what causes morphogenesis, the development of form, is cell migration and movement.

9. What are the differences between sea urchin early development and chick early development? Why are those differences necessary?

 The main differences have to do with the early maturation of the aquatic sea urchin compared with the longer maturation process of the terrestrial chick egg. The sea urchin egg hatches as a blastula after only about 24 hours of development and can swim around and fend for itself. The chick, in contrast, must develop to a much more mature stage before it hatches after about 3 weeks. The much longer pre-hatching development requires several additional features of the chick egg. To maintain the chick embryo in the terrestrial environment, there must be an egg shell to protect it but allow gas exchange. The gas exchange function is facilitated by the vascularized chorion membrane as the chick gets larger. Development must occur in water, so the embryo proper is surrounded by a membranous, water-filled sac called the amnion. The chick needs a food supply, the yolk, which is surrounded by the vascularized yolk sac that allows blood to pick up nutrients and deliver them to the growing embryo. Finally, the chick produces nitrogenous waste that must be stored until hatching in the membranous sac called the allantois.

10 Why are bird eggs so much bigger than mammal eggs?

 Bird eggs must store all the food the growing embryo needs. This yolk takes up the majority of the volume of the egg. Mammal eggs don't store food for the embyro because the embryo will be nourished by the mother through the placenta.