What provides nutrition for embryonic development?

In the early stage of embryonic development, it is mainly in the uterine cavity after the fertilized egg develops into a blastocyst, implants on the uterine wall, and invades the uterine wall, so the nutrition is mainly provided by the uterine wall, and the cyst fluid in the blastocyst gives rich nutrition.

At this time, the blood circulation of the placenta and umbilical cord has not yet been established with the blood circulation of the mother. This association mainly exists in the nutrition under the local microenvironment in the uterus, so it is necessary to protect the effective circulation in the uterus, and after the placenta is separated from the circulation, the umbilical cord and placenta can supply blood and oxygen to the fetus.

The nutrients needed for fetal development are transmitted through the placenta and umbilical cord, so the placenta and umbilical cord are an important link between the mother and the fetus.

The fetus and the mother are connected by the placenta and the umbilical cord, which attaches to the uterine wall and directly absorbs nutrients from the mother, and then passes through the umbilical cord to the fetus. Therefore, we can see that the placenta and the nutritional intake of the pregnant mother are the key factors that directly affect the nutrition of the fetus. In terms of placenta, the size of the placenta area, the thickness of the placenta, the aging of the placenta and the pathological changes of the placenta will affect the nutrient absorption of the fetus, so when doing a pregnancy test, in addition to checking the development of the fetus, the doctor will also check the condition of the placenta.

In terms of nutritional intake of pregnant mothers, the nutrients ingested, digested and absorbed are the source of fetal nutrition, so pregnant mothers need to take in nutrients reasonably and scientifically according to the dietary guidance plan during pregnancy or the doctor's advice, combined with different periods of pregnancy and different critical periods of fetal development, to ensure the nutrition of the fetus.

The nutrients needed in the early stages of human embryonic development come from the yolk. The trophoblast, amniotic cavity, and yolk sac are accessory structures that provide nutrients and play a protective role.

In the second week of blastocyst implantation, the cells of the inner cell population also proliferate and differentiate, gradually forming an embryonicdisc with two germ layers, the inner and outer germ layers. The perimeter of the endoderm extends downwards to form another sac, the yolk sac, so the endoderm forms the top of the yolk sac.

Choose C, (because the title is about embryonic development, not early embryonic development.) Note that I provide to see the third article, because the title does not make it clear whether it is direct or indirect**, so I think it is direct**, if it is indirect**, it is the parent choice d).

Egg yolk is a nutrient stored in animal eggs, it is a nutrient for oviparous and ovoviviparous animal embryonic development, viviparous mammalian egg cells also have yolk, is a nutrient in the early stage of embryonic development

Placental functions include gas exchange, nutrient removal**, elimination of fetal metabolites, defense functions, and synthesis functions.

The nutrients needed in the early stages of embryonic development come from the yolk, and the main nutrients for embryonic development are obtained from the mother through the placenta

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The uterus is the site of embryo and fetal development; The umbilical cord fetus obtains the nutrients and oxygen required from the mother through the placenta and umbilical cord, and at the same time discharges the carbon dioxide and other waste products into the mother's blood, and then excretes them from the body by the mother; The yolk provides nutrients for the initial embryonic development; The mother provides nutrients for embryonic development

Therefore, c

The embryo is the main structure of the seed, and it includes the cotyledons.

The four parts of germ, hypocotyl, and radicle are the cotyledons or endosperm that provide nutrients for embryo development

So the answer is: germ; hypocotyls; Radicle; Cotyledon; Cotyledon; Endosperm.