Sexual Reproduction in Flowering Plants

Sexual Reproduction in Flowering Plants: The reproductive part of a flowering plant is the flower. Flowers are considered to be modified shoots. It is consist of parts like corolla, calyx, androecium and gynoecium. Calyx and corolla perform the function of attracting pollinators.

Androecium :  It is male reproductive part of flower, consists stamen. An androecium is consist of an anther and filament . Anther contains the male gametes.

Gynoecium : It is the female reproductive part of the flower. It forms the pistil. It is consist of  three parts stigma , style and ovary.

Pollination  : The pollen grain (male gamete) from anther is transferred with the help of agents like wind, water, insects, birds,  animals etc. The process of transfer of pollen is called as pollination.The pollen after transfer stays on the stigma of Gynoecium and transfer the male gametes to the ovary by pollen tube. This transferred pollen reaches the ovary  through style.

Fertilization in Plants :

In plants sexes may or may not be separated. Accordingly, a flower is either unisexual (bearing either male or female gamete or ova) or bisexual (bearing both gametes). The pollen grain represent the male gametophyte and embryo sac represents the female gametophyte which encloses the egg. The transfer of pollen grain from anther to the stigma of other flower is called as cross pollination and if the pollen get transferred to the stigma of same flower it is called as self pollination.

After reaching the stigma pollen grains germinate on the stigma. The inner wall of the pollen grain grows into a pollen tube, which grows down through the style and finally reaches the ovule. Inside the ovule, a male gamete fuses with the female gamete and a zygote is formed. This is known as fertilization.

he zygote divides repeatedly to form the embryo (future plant) in the ovule. The embryo possesses a tiny future root (radicle), a tiny future shoot (plumule) and cotyledons to store food. The ovary grows rapidly to form the fruit. The ovary wall ripens and forms the fruit wall. The sepals, petals, stamens, style and stigma of the flower degenerate and usually fall off. Sometimes the sepals may persist in the fruit. The ovule develops into a seed. The wall of the ovule thickens to form the protective seed coat. The seed loses water and becomes hard and dry. Seeds can withstand drought and other adverse conditions in this state. This is an advantage for seed-producing plants. The embryo lies dormant in the seed, but under favourable environmental conditions it becomes active and germinates to form a small seedling. The radicle forms the root while the plumule forms the shoot. The growing root and shoot utilize the food stored in the cotyledons.

Sexual Reproduction In Plants : -  The different parts of the flower are attached to the nodes. All the structures present at one node are collectively called the whorl. The first or the outermost two whorls are called the non-reproductive or accessary whorls. They are the calyx and corolla. The inner two whorls are androecium and gynoccium, the reproductive or necessary whorl. A flower may have either androecium or gynoecium. In such cases the flower is called unisexual. For example sunflower. If the flower contains both androecium and gynoecium it is called bisexual. For e.g. Hibiscus and Mustard. Parts of a Flower: - A typical flower consists of following parts –

(i) Sepals : It is the outer whorl of the flower. It is usually green in colour but in some flower it may be coloured to attract insects. It protects the inner whorls of the flower.

(ii) Petals : It is the second whorl of flower and consists of coloured petals. Being coloured in nature they attract various insects and animals for pollination.

(iii) Stamen : It is male reproductive part of a flower. Each stamen consists of a stalk called filament and a flattened top called the anther. The anthers produce pollen grains which produces male gametes. The pollen grains appear as yellowish powder which sticks to our hands. The male germ cell or the male gamete is produced by the pollen grain.

(iv) Carpel: Carpels have a swollen ovary at the base, an alongated middle style and a terminal stigma. The ovary contains ovules. Each ovule possess an egg which is the female gamete.