Question

24, 2020 online lecture ork. Due in 2 days 4/6 answered orion allows was exchange Shell Chorion Yolk sac contains nutrients Albumen provides water suiequo Amnion Allantois contains waste Fig 32.9 Amniotic eggs: 1) Help keep the embryo from drying out 2) Provide nutrients & support to the embryo 3) Are laid on dry land by most reptiles (including birds) and egg-laying mammals Compared to the amphibian egg, with just one jelly-like layer, amniotic eggs have 4 membranous sacs that enclose the embryo. The egg cell gets fertilized internally by a sperm cell before the membranes 3 Fullscreen

i added the figures. im having problems understanding!

Answer 1

Amphibians have a jell surrounding their eggs which are released in to the water to prevent dessication. Reptiles, birds and mammals have a fluid filled sac covering their embryos called amnion which does not allow their enbryos to dry. Because of the amnion and the fluid present surrounding the embryos, the eggs can be laid on the land also. That is how, dependence on the water for reproduction stopped. There are other membranes present along with the amnion , which are yolk sac, allantois and chorion. There are 4 such extra embryonic membranes protecting and serving the embryo during its development. All the four extra embryonic membranes protect, nourish and serve the embryo during embryonic development. In the reptile ,bird and mammals these membranes are found surrounding the embryo.

The function of yplk sac is to surround the yolk and provide nourishment to the growing embryo. It has lot of blood vessels in its membrane, which help in carrying the nutrients in to the growing embryo body. Birds have big yolk sac as they have lot of yolk in their yolk sac. Birds depend on the yolk for their nourishment as the birds are egg laying animals.

In mammals, the yolk sac is very small because mammals give birth to young ones. They do not store yolk in the yolk sac. The nourishment is obtained from the mothers circulation. That is why the yolk sac is very small. But the yolk sac is not completely lost in mammals because it is important in circulation of nutrients in the early stages of developent though it does not store yolk in it.

In mammals well developed placenta formed between the mothers uterine wall and the foetal tissues, supplies nutrition through out the embryonic development.