Question

1.

- The type of egg in mammals

- The cells of any blastula

- The type of blastula in mammals

- The type of cleavage in mammals

- The fluid-filled cavity of any blastula

- The two germ layers that form the chorion in mammals

- The two membranes composed of mesoderm and endoderm

2. During vertebrate development, the germ layers (i.e. ectoderm, mesoderm, endoderm) not only give rise to the embryo itself, but they also contribute to the extraembryonic membranes including the chorion, amnion, allantois, and yolk sac.

Discuss the similarities and differences between the allantois and the yolk sac, and then propose why the yolk sac is much larger in the chicken than in the human.

Answer 1

1. a, The type of egg in mammals- alecithal egg ( egg with no yolk).

b, The cells of blastula - blastomere

c, the type of blastula in mammal- blastocyst

d, type of cleavage in mammal- holoblastic

e, fluid filled cavity of blastula- blastocoel

f, two germ layer that form chorion- trophoblastic ectoderm & extramembryonic mesoderm

2. allantois is an sac like extraembryonic membrane that removes wastes from embryo.it also exchange oxygen and carbondioxide with the air outside the eggshell. it serves as a disposal site for uric acid.

yolk sac is also an extraembryonic membrane that surroun eggyolk. it provide nourishment for the embryo. helps in circulation and delivering nutrients.

Human have smaller yolk sac because, the yolk sac acts as the preliminary circulatory system and is eventually absorbed into the gut of the embryo. but in chicken, in the earlie stages yolk sac gives nourishment and any remaining, unused yolk material in the yolk sac when the chicken hatches from the egg is drawn into the abdomen for use by the chicken for the first two to three days after hatching while the chicken learns what to eat/drink and where to find it.