In human females, yolk sac which is the embryonic layer becomes non-functional in the later part of the gestation period. Give reason.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Yolk Sac**: The yolk sac is an embryonic structure that initially provides nutrition to the developing embryo. It is one of the first structures formed during early embryonic development.

2. **Role of the Yolk Sac**: In the early stages of gestation, the yolk sac supplies essential nutrients to the embryo. This is crucial as the embryo is not yet fully developed and relies on this source of nutrition.

3. **Formation of the Placenta**: As the embryo grows, it undergoes implantation into the uterine wall. This is when the placenta begins to form. The placenta is a vital organ that develops during pregnancy and serves multiple functions, including nutrient transfer, waste removal, and gas exchange between the mother and the embryo.

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