Reproduction: Reproductive Structure of Flowers

Angiosperms are flowering plants that reproduce sexually. The flower is the main component of plant reproduction. It has both the male as well as the female gametes. Although some parts of the flower are sterile, they all aid in reproduction. We need to examine the functions and parts of each flower in order to understand how they reproduce.

Learn about sexual reproduction in flowering plants and how it works.

Flower structure

These are the parts of a flower:

Calyx: This is the outermost part of a flower. It is made up of units known as sepals. The rest of the flower is enclosed by the calyx in the bud stage. They are usually green in colour, but they can also be pink or purple. This is called petaloid. Calyx can be either prominent or absent.

Corolla: It is composed of many petals and it’s the second whorl. Sometimes, these petals can be fragrant. These petals are often fragrant and come in a variety of colours.

Reproductive Structure of Flowers

Androecium

It is the male reproductive portion of a flower and includes stamens. Each stamen consists of two parts: the anther and the filament. The filament supports the tip of the anther. These pollens are created by meiosis, and eventually disappear.

• Anther – This structure is responsible for the formation of pollen.
• Filaments -These thread-like structures attach to the anther and keep it in place.

When a transverse section of an anther is viewed, it showcases two microsporangia each located in the two lobes. The microsporangia further become pollen sacs. The pollen sac is made up of pollen grains.

Microsporangia & Microsporogenesis

Microsporogenesis is the process of creating microspores by meiotic division from microspore mother cells.

nther’s structure: Anther is the breeding area for stamens. Two lobes connect each anther. Each anther lobe contains two pollen chambers that are located longitudinally. A number of pollen microspores are sufficient to supply the microsporangium.

Structure of Microsporangia

Microsporangia is made up of:

1. Tarentum- These cells are multinucleate, and this layer is one the innermost layers
2. The middle layer consists of three to four layers made up of thin-walled cells. They are found just below the endothelium
3. Endothecium- This layer lies within the epidermis. Endothelium cells are formed by some cells
4. Epidermis- This is the protective outermost single-layer. The epidermis cells in Arceuthobium become fibrous thickened and are designated exothecium

• Formation and use of pollen grains: The young anther quickly becomes four-lobed because it contains homogenous mass parenchymatous cells that are regarded by the epidermis. Each archesporial that is initially found in hypodermal cells splits into the outer primary sporogenous and inner primary parietal cells. Each primary sporogenous cell splits to make microsporocytes. Each microspore mother cell meiotically divides into pollen grains.
• Microgametogenesis: Microspore, which is the first cell in the male gametophyte’s development, is only partially developed. The pollen grain wall is composed of exine (outer) and inline. The outer layer contains sporopollenin, while the inner layer is composed of pectose & cellulose.
• Development of microspores in situ. The spore wall is surrounded by a smaller generative cell. The generative cell is covered with a callose layer. The callose layer is then removed. The pollen grains are then released by the anther. Through pollination, the pollen grains that have been released are passed on to the stigma. The stigma’s pollen grains absorb water and swell within minutes. The pollen tube’s wall secretes hydrolytic enzymes as well as exogenous pectinases, allowing for entry. The pollen tube supplies both the generative and vegetative cell types. The generative cell splits, forming two non-motile male gametes. As there is no vital function, the tube nucleus could disintegrate.

Gynoecium

It is the female reproductive system and the last flower whorl. It is made up of pistil and occupies a central position in the thalamus. The pistil is made up of three components: the stigma, style and ovary. Internally, ovules are produced by the ovary. Megaspores are produced by meiosis and then turn into female gametophytes. Egg cells are thus produced.

Gynoecium may be:

Monocarpellary – The gynoecium is made up of one pistil. Peas and beans are examples

Multicarpellary – Here, a gynoecium includes more than one pistil

Syncarpous – It’s the gynoecium that has a combined pistil. For eg., Tomato, cucumber

Apocarpous -It’s the gynoecium that comes with a free pistil. For eg., Lotus vinca

Pistil– Each pistil has three parts

• Ovary – The ovary (or ovary) is a place where the ovules, or eggs, are kept until fertilisation
• Stigma – It attaches to the top carpel where pollen from other flowers land
• Style – It is a tubular structure connecting the stigma and the ovary. It transports pollen from the stigma into the ovary, and holds the stigma in place

Megasporangia & Megasporogenesis

The funicle is a stalk that connects the ovule to the placenta. Megasporocytes are formed from these megasporocytes. Megasporogenesis refers to the arrangement of megaspores from the megaspore mom cell. The megaspore mom cell divides meiotically. While the other megaspores degenerate, one of the three megaspores can be used. The female gametophyte is formed by the functional megaspore.

Pollination

All flowering plants participate in pollination, which is an ecological process. The matured pollen grains from this process are transferred from the anther to the stigma in order to reproduce in flowering plants.

There are two types:

• Self-Pollination This is when pollen grains from an anther are deposited on the stigmas of the same or another flower on the plant

• Cross-Pollination This is when pollen grains from one flower are transferred to another flower’s stigma

Fertilisation

The pollen tube transfers the pollen to the ovary after pollination. Once the pollen tube reaches the ovary one of the male and female gametes will mate with the ovule or fertilise the other. A zygote is formed when the gamete and eggs unite. This progressively develops into an embryo. The endosperm nucleus is formed when the second gamete combines with the polar nuclei. It provides nourishment for the embryo. The fertilisation process ultimately transforms the ovules into seeds, while the ovary becomes the fruit.

Functions of a flower

• The primary function of the flower’s flowers is to reproduce the individual and the species
• These are modifications to a shoot. Different shapes of angiosperms are used to pollinate flowers in different ways
• Heterosporous flowering plants produce two types of spores. Megaspores can be found in ovules, while Microspores can be produced by meiosis within anthers
• The development of the pollen tube and base germination are all done by flowers. They also help in the formation of gametes, fertilisation, and the creation of the pollen tube. The fruit is supplied with the ovarian portion from the carpel. After fertilization, the ovules become seeds. In the case of heterosporous plants, gametophytes can also grow inside the spores
• Unisexual flowers are those that lack one or both of the reproductive organs. Different modifications in ovaries aid in dispersal of seeds or fruits in certain floral parts, such as a calyx