At which side of embryo sac the development of embryo takes place?

At micropylar end.

In the embryo sac of a flowering plant, the development of the embryo takes place at the micropylar end. The micropyle is a small opening or passage near the apex of the embryo sac through which the pollen tube enters during fertilization.

After successful fertilization, the zygote, which is the result of the fusion of the sperm and egg cells, undergoes subsequent divisions and develops into an embryo. This embryonic development occurs at the micropylar end of the embryo sac.

The micropylar end is typically located near the opening of the ovule, and it is where the pollen tube delivers the sperm cells for fertilization. Once fertilization occurs, the embryo begins to form and develop within the embryo sac, near the micropylar end.

It's important to note that the chalazal end of the embryo sac is located opposite to the micropylar end. The chalaza is the basal region of the ovule where the integuments and nucellus join together. While the chalazal end plays a role in nutrient transfer and storage, the development of the embryo primarily takes place at the micropylar end.