What is sexual reproduction in flowering plants definition?

What is sexual reproduction in flowering plants definition?

Sexual reproduction in flowering plants

Sexual reproduction can be defined as the process through which new organisms are produced due to the fusion of male and female gametes from two parents. For sexual reproduction in flowering plants, both male and female gametes are needed and the process of such reproduction involves the different parts of a flower. It also needs external pollinating vectors.

Reproductive structure of flower

A flower is the main reproductive organ of a plant having both male and female reproductive parts.

• Androecium- The main reproductive organ in plants is known as androecium. Its function is to produce and store pollen. The unit is androecium called stamen. Androecium is made up of many stamens. A stamen has two parts. They are filament and anther.

-Filament: Filament is like a stalk which is attached to a flower and it provides support to one another.

-Anther: Anther is oval in shape and it is the pollen-producing part of aflower.

The transverse section of an anther is called microsporangia which forms a pollen sac. The pollen sac consists of pollen grains.

• Microsporangia and microsporogenesis

Microsporogenesis forms microspores from microspore mother cells by meiotic division.

The structure of anther: The anther is considered as the breeding part of stamens connected by two lobes. Each anther lobe consists of tow pollen chambers which are placed longitudinally. The microsporangium is supplied by many pollen microspores.

Structure of microsporangia

Microsporangia contains the following:

1. Tarentum: It is the innermost layers of the wall. The cells are multinucleate.
2. Middle layer: It is made of three to four layers of thin-walled cells located just below the endothelium.
3. Endothecium: It is inside the epidermis.
4. Epidermis: It is the outermost protective single-layer. Cells of the epidermis in Arceuthobium grows a fibrous thickening and the epidermis is termed as exothecium.

Formation of pollen grains

The young anther turns into four-lobed as it consists of a homogenous mass of parenchymatous cells encircled by the epidermis. Each archesporial which are present in hypodermal cells are classified into inner primary sporogenous cell and outer primary parietal cell. Each primary sporogenous cell divides to produce microsporocytes. Each microspore mother cell meiotically splits to form pollen grains.

Microgametogenesis (Development of male gametophyte)

This is the first cell of the male gametophyte. Microspore gets developed partially. The wall of the pollen grain consists of exine (outer layer) and inline (inner layer). The outer layer I made of sporopollenin and the inner layer comprises of pectose and cellulose.

• Gynoecium- Gynoecium is the female reproductive organ in plants. Its function is the internal production of ovules which ultimately produces an egg. Gynoecium consists of three parts- stigma, style and ovary.

-Stigma: The anterior part of a carpel is stigma. Here, pollen germinates.

-Style: Style is a tube-like filament which connects the stigma and ovary. It helps to pass the pollen from stigma to ovary.

-Ovary: Ovary is a small chamber where ovules are formed.

Gynoecium can be any one of the following:

Monocarpellary: It has a single pistil. For example: peas and beans.

Multicarpellary: It has more than one pistil.

Syncarpous: It has combined pistil. For example, tomato, cucumber

Apocarpous; It has free pistil. For example, lotus vinca

• Megasporogenesis- It is the process of formation of megaspores within megasporangium. Megaspores comes from ovules by way of meiosis. These megaspores lead to the formation of the female gametophyte. One megaspore change into gametophyte and the others die out. The basal megaspore turns into embryo sac.

The male and female gametes come from microsporogenesis and megasporogenesis respectively. They are the basic units of sexual reproduction in flowers.

Pollination

Pollination is an external process that transfers pollen grains from the anther to stigma. There are two types of pollination. They are self-pollination and cross-pollination.

• Self-pollination- Here, the pollen grains stay in the originating flower.
• Cross-pollination- Here, pollen from one flower gets transferred to another through vectors like bees and air.

Fertilization

Fertilization is the next stage after pollination when the pollen grains reach the ovary. The male gamete fuses with the female gamete, ovule, to make a zygote. The ovary converts into a fruit and the fertilized ovules converts into seeds.

Do you know the answer of the below question?

1. Assertion. The endosperms is generally triploid (3n). Reason. It develops from primary endosperm nucleus formed by fusion of haploid male gamete and diploid secondary nucleus.

Functions of a flower

Let us have a look at the functions of a flower below: 

• The most important function of the flower is to reproduce the individual and the species.
• Flowers are the modifications of a shoot. Angiosperms of flowers are shaped for many different modes of pollination.
• Flowering plants are heterosporous producing two types of spores. Megaspores are produced in ovules and microspores are produced by meiosis in anthers.
• Flowers helps in the development of the pollen tube, base germination of pollen, fertilization and to form gametes. The ovarian part of the carpel is given into the fruit. The ovules are turned into seeds after fertilization. The gametophytes also grow inside the spores in the case of heterosporous plants.
• The flowers which do not have one or other reproductive organ are known as unisexual or imperfect.