In angiosperms , which of the following structure always precedes the development of embryo?

Formation of endosperm.

The correct answer is option (4) -Formation of endosperm.

During double fertilisation in angiosperms, one male gamete fuses with the egg to form the diploid zygote (syngamy or generative fertilisation). The diploid zygote finally develops into embryo. The other male gamete fuses with the two polar nuclei(or secondary nucleus) to form the triploid primary endosperm nucleus, PEN .This fusion of three haploid nuclei is referred to as triple fusion.In flowering plants, both syngamy and triple fusion occur within the embryo sac, giving rise to the term "double fertilization," which is unique to flowering plants. The central cell, after undergoing triple fusion, becomes the primary endosperm cell (PEC), which develops into the endosperm. On the other hand, the zygote develops into an embryo.

• Endosperm formation occurs first in angiosperms because it serves as a nutritive tissue for the developing embryo.
• It is formed through triple fusion (fusion of a male gamete with two polar nuclei) in the central cell of the embryo sac.
• The endosperm supplies carbohydrates, proteins, and nutrients, ensuring proper embryo growth and differentiation.
• Once the endosperm is established, the zygote starts developing into an embryo, utilizing the stored nutrients.

This process is essential for seed development and ensures successful germination in many angiosperms.