Understanding Embryo Development in Flowering Plants

In flowering plants, the process of reproduction involves pollination and fertilisation. Following successful pollination, the pollen grain germinates on the stigma and grows a pollen tube down to the ovule, carrying the male gametes.

The Fertilisation Process and Zygote Formation

Fertilisation occurs within the ovule. In flowering plants, a unique process called double fertilisation takes place. One male gamete fuses with the egg cell to form the diploid zygote. The other male gamete fuses with the central cell to form the primary endosperm nucleus, which develops into the endosperm, a nutritive tissue.

Embryo Development Site

After fertilisation, the zygote is located inside the ovule. The zygote then undergoes repeated cell divisions (mitosis) and differentiation. This process of division and development of the zygote into a multi-cellular structure with an embryonic axis and often cotyledons is called embryogenesis. This crucial development of the embryo from the zygote occurs entirely within the protective environment of the ovule.

Therefore, in flowering plants, after fertilisation, the zygote divides several times to form an embryo within the ovule.

Analysis of Options

• Stamen: The stamen is the male reproductive part of a flower, producing pollen. It is not involved in the development of the embryo after fertilization.
• Ovule: The ovule contains the female gamete (egg cell) and the central cell. Fertilisation occurs here, and the zygote formed within the ovule develops into the embryo. This is the correct site.
• Stigma: The stigma is the receptive tip of the pistil where pollen lands. It is involved in pollination but not in embryo development.
• Pollen tube: The pollen tube is a structure that grows from the pollen grain to transport the male gametes to the ovule for fertilisation. It is a pathway, not the site of embryo development.

Post-Fertilisation Changes

Following fertilisation and embryo development within the ovule, several changes occur:

• The ovule matures and develops into a seed. The seed contains the embryo and the stored food (endosperm or cotyledons).
• The ovary, which encloses the ovules, matures and develops into a fruit.
• Other floral parts like petals, sepals, stamens, stigma, and style usually wither and fall off.

The formation of the embryo within the ovule is a key step in the formation of a seed, which is essential for the propagation of flowering plants.

Additional Information: Embryo Structure

The structure of the mature embryo varies between different types of flowering plants, specifically monocots and dicots.

• In dicots, the embryo typically consists of an embryonal axis (radicle, plumule, hypocotyl, epicotyl) and two cotyledons, which often store food.
• In monocots, the embryo has an embryonal axis and a single cotyledon (scutellum). It also has protective sheaths like the coleoptile (covering plumule) and coleorhiza (covering radicle).

Regardless of the specific structure, the embryo's initial development from the zygote always occurs inside the ovule.