What is the Difference Between Embryo Sac and Ovule

The main difference between embryo sac and ovule is that the embryo sac is the female gametophyte of flowering plants and is a multicellular structure inside the ovule, whereas ovule is an outgrowth of the ovary of a seed plant that is a megasporangium.

The female reproductive system of a flowering plant consists of several structures, including the ovary, style, and stigma. These structures are located in the center of the flower. The ovary has one or more ovules, which are structures that develop into seeds after fertilization.

Key Areas Covered

1. What is an Embryo Sac
– Definition, Features, Function
2. What is an Ovule
– Definition, Features, Function
3. Difference Between Embryo Sac and Ovule
– Comparison of Key Differences

Key Terms

Embryo Sac, Ovule

What is an Embryo Sac

The embryo sac, or the female gametophyte, is an oval structure found in the ovule of flowering plants. It is a multicellular structure. It contains the egg cell, which is fertilized by a sperm cell during sexual reproduction. The embryo sac forms when a haploid megaspore nucleus divides. Moreover, it has two haploid nuclei and six haploid cells with no cell walls. But in certain cases, these two haploid polar nuclei can fuse to form a single endosperm mother cell.

Formation of the embryo sac involves two stages. Stage one involves megasporogenesis occurs; here, the haploid megaspore tetrad begins to form due to the meiosis of a single diploid mother cell. Out of these, three degenerate, and one remains, and the one that remains later develops into the embryo sac. In stage two, megagametogenesis occurs; this involves the formation of the embryo sac as a result of the mitosis of the functional haploid megaspore to produce an 8-nucleate, 7-celled gametophyte. Then the polar nuclei move to the center out of all the eight nuclei to combine and create a single diploid cell at that location.

Figure 1: Embryo Sac (A: micropylar end B: chalazal end C: egg cell D: synergids E: polar nuclei F: antipodals)

The single diploid cell later fuses with the sperm to form a triploid endosperm. The rest of the cells grow into antipodal cells, while two cells modify into synergid cells, which degenerate gradually. Moreover, successful fertilization of the embryo sac is necessary for the production of viable seeds.

What is an Ovule

Ovule is an outgrowth of the ovary of a seed plant that is a megasporangium and encloses an embryo within a nucellus. It gives rise to seeds after fertilization. Moreover, there are three primary parts of the ovule: integuments, nucellus, and female gametophyte. Integument is the outermost layer of the ovule, which consists of two layers as the inner integument and the outer integument. Meanwhile, the nucellus is located inside the integument and is a mass of tissue that surrounds the female gametophyte. In addition, the female gametophyte is the innermost part of the ovule.

Compare Embryo Sac and Ovule - What's the difference?

Figure 2: Ovule

After fertilization, the ovary begins to develop. First, the wall of the ovary gets thick. This happens to transform the structure into a seed. Then the ovary begins to grow around it, later transforming into a fruit. In plants like avocados, there is a single ovule in the ovary. However, certain plants like kiwifruit have numerous ovules, which later mature into a number of seeds.

Moreover, the ovules can be divided into six groups based on their morphologies. They are atropous, anatropous, amphitropous, hemianatropous, campylotropous, and circinotropous.

Difference Between Embryo Sac and Ovule

Definition

The embryo sac or female gametophyte is an oval structure found in the ovule of flowering plants. Ovule is an outgrowth of the ovary of a seed plant, and it is a megasporangium that encloses an embryo within a nucellus.

Function

The embryo sac is the site for fertilization, whereas the ovule houses the embryo sac.

Conclusion

The embryo sac and ovules are both parts of the female reproductive system of flowering plants. However, they have structural differences between them. The main difference between embryo sac and ovule is that the embryo sac is the female gametophyte of flowering plants and a multicellular structure that is formed inside the ovule whereas the ovule is an outgrowth of the ovary of a seed plant that is a megasporangium.

Reference:

1. “How Is The Embryo Sac Formed.” Byju’s.
2. “Ovule – Definition, Functions and Structure.” Toppr.