BOTANY –STRUCTURE OF OVULE Presentation by Karthika Dass
- 1. BOTANY – STRUCTURE OF OVULE KARTHIKA DASS
- 2. OVERVIEW OF A TOPIC DEFINITION LOCATION STRUCTUREOF OVUM
- 3. DEFINITION The ovule is a component of the female reproductive system of seed plants. It is where female reproductive parts are produced and maintained. Ovules are housed in ovaries at the base of the carpel, which includes an aperture at the top, stigma, and a neck called a style. After fertilisation, these cells eventually develop into a seed, which subsequently ripens to form a full-grown adult plant. Ovule is also known as the megasporangium in flowering plants.
- 4. LOCATION The ovule is found inside the gynoecium, a part of the flower present in angiosperms or flowering plants. The fruit wall eventually develops from the ovary of the gynoecium, which produces more than one ovule. A funiculus structure, resembling a stalk, connects the ovules to the placenta. Plant species exhibit various ovule attachment or placentation patterns, including:
- 5. The ovule is composed of the integuments forming the outermost layer, the nucellus, and the female gametophyte (known as an embryo sac in angiosperms), found in the core. STRUCTURE OF OVUM
- 6. Integuments: A layer of protection surrounds the ovule called an integument. Once the ovule has undergone fertilisation, the integuments transform into the seed coat. Gymnosperms usually have one integument (unitegmic), whereas angiosperms typically possess two integuments (bitegmic).
- 7. The chalaza: • where the nucellus and integuments are connected, is located across from the micropyle. • The integuments do not entirely encase the nucellus; a small gap called the micropyle remains at the apex. • A male gametophyte, pollen, can enter the ovule through the micropyle opening and fertilise it.
- 8. Nucellus: The most significant component of the ovule is the nucellus. It contains nutritive tissue and the embryo sac, and in some flowering plants, it is still present after fertilisation as a source of nutrition for the embryo. The nucellus, a component of the ovule’s inner structure, forms a layer of sporophytic or diploid cells near the integuments. Nucellar embryony, an asexual reproduction process that occurs in some plants, allows the diploid nucellus tissue to give birth to the embryo inside the seed. The perisperm nourishing the embryo may grow from the nucellus after fertilisation.
- 9. What are Antipodals and Synergids? During fertilization process, a pollen tube grows into one of the synergid cells, ceases growth, ruptures and releases its two sperm cells into this cell. Generally, antipodal cells are present in the chalazal end. Antipodals are nutritive in function and they nourishes the embryo sac.
- 10. STRUCTURE OF OVUM WHAT IS RAPHE ? Raphe is an elongated mass of tissue, containing vascular bundle, and lying on the side of an anatropous ovule, between the chalaza and the attachment to the placenta. Hilum is the scar on the Testa where it was attached to the funicle. Chalaza is the opposite side of the side bearing micropyle of an ovule. WHAT IS HILUM? These are scars on the seed coat which marks the place at which seeds get fastened to the tissues of the ovaries. These regulate the dynamics between the embryo and the external surroundings. They form a potential route for the invasion of pathogens in seeds. The permeability of seeds is based on various aspects, such as the cutin. WHAT IS MICROPYLE? Small pores are seen at one terminal of the hilum of seeds. It is from here that the pollen tube gets into the ovaries at the time of fertilisation. At the time of germination of seeds, water passes in the seed through the micropyle, and it serves as the path for invasion of pathogens in seeds, as seen in Hilum.
- 11. FUNCTIONS OF OVUM The ovule is an essential component in sexual reproduction. A pollen grain develops a pollen tube through the style after contacting the stigma of a flower of the same species. This tube subsequently reaches the ovary and travels to the ovule. After that, fertilisation can occur as the pollen grain’s nucleus travels down the tube to combine with the nucleus inside the embryo sac. It should be noted that pollen, which includes the male gametophytes, serves as the male equivalent of the embryo sac.