Structure of a Flower

 

XII BIOLOGY
CH-1 Reproduction in lower and higher plants

PART-  

Structure of a Flower

Flower –

 A flower is the reproductive structure of flowering plants in angiosperms and is designed to help in pollination and seed production.

Complete flower:

Has all four whorls (calyx, corolla, androecium, gynoecium).

Incomplete flower:

Missing one or more whorls.

Structure of a Flower –

These whorls include both non-reproductive and reproductive parts.

It has four main whorls /parts-

 some are reproductive and some are non-reproductive.

 Pedicel:

The stalk that supports the flower.

Thalamus (Receptacle):

 The swollen tip of the pedicel where floral parts are attached.

1. Non-Reproductive Parts (Accessory parts)

a) Calyx –

Made up of Sepals,Usually green, leaf-like structures at the base of the flower.

Function: Protects the flower bud before it opens.

b) Corolla-

 Made up of Petals,Brightly colored and often scented to attract pollinators.

Function: Helps in pollination by attracting insects, birds, etc.

2. Reproductive Parts

a)Androecium –

It is Male reproductive part,Made up of stamens.

Each stamen has:The stamen consists of the anther, connective and filament.

Anther:

Produces pollen grains containing male gametes.

Connective:

attachment to Antherand Filament

Filament:

Stalk that holds the anther.

Function: Produces and presents pollen for pollination.

b) Gynoecium- 

It is Female reproductive part.Made up of  carpels/Pistil.  Each carpel has:

Stigma: Sticky surface to catch pollen.

Style: Tube that connects stigma to ovary.

Ovary: Contains ovules, which develop into seeds after fertilization.Function: Produces ovules and receives pollen for fertilization.

Function: Reproductive Produces ovules, site of fertilization 

Parts of a Flower

The calyx, corolla, androecium, and gynoecium are four whorls of modified leaves that constitute the flower. The sepals, petals, stamens, and pistils, respectively, constitute one of the flower parts in each of these whorls.

Vegetative Parts of a Flower

The vegetative part of a flower consists of the following:

Petals: This is a bright-coloured part that attracts bees, insects, and birds. The colour of petals varies from plant to plant; some are bright while some are pale coloured. Thus, petals help us to differentiate one flower from another.

Sepals: Sepal is the green-coloured part beneath the petals to protect rising buds. Some flowers have fused petals-sepals while a few have separated petals-sepals.

Reproductive Parts of a Flower

Flowers contain the plant’s reproductive structures.

The reproductive parts of a flower consist of the following:

Stamen: This is the male reproductive organ and is also known as Androecium. It consists of two parts namely: anther and filaments.

The anther is a yellowish, sac-like structure, involved in producing and storing the pollens.

The filament is a slender, threadlike object, which functions by supporting the anther.

Pistil: This is the innermost part and the female reproductive organ of a flower which comprises three parts -stigma, style and ovary. This is collectively known as the pistil.

Stigma: It is the topmost part or receptive tip of carpels in the gynoecium of a flower.

Style: It is the long tube-like slender stalk that connects the stigma and the ovary.

Ovary: It is the ductless reproductive gland that holds a lot of ovules.

Whorls

Along with the vegetative and reproductive parts, a flower is also composed of four whorls, which are largely responsible for the radial arrangement of a flower. A typical flower has a circular section with a common centre, which can be clearly observed and distinguished from the top of the flower. There four whorls are:

Calyx

The calyx is the outermost whorl of a flower. It comprises sepals, and tiny leaves present at the base of a flower. These protect the flower whorls against mechanical injuries and desiccation. Some plants have coloured sepals the calyx and are called petaloid.

If the sepals are free the calyx is called polysepalous, and if they are united it is called gamosepalous.

In many flowers, the sepals fall off before the flower even opens fully. Such sepals are known as caducous.

In some, the sepals fall off after fertilization. Such sepals are known as deciduous.

The persistent sepals remain up to the fruiting stage.

Corolla

This is the second whorl of a flower. It contains petals which serve two main functions:

• To attract pollinators.
• To protect the reproductive parts of a flower

Petals are brightly coloured and scented to attract animals and insects for pollination. The calyx and corolla are collectively called the perianth.

Different forms of the corolla are found in the flowers.

• Polypetalous Regular
• Polypetalous Irregular
• Gamopetalous Regular
• Gamopetalous Irregular

Stamens 

Stamen is also known as the third whorl of the flower and is the male reproductive part. It consists of a filament which is a thread-like structure with a circular structure anther on the top. Pollen is produced by the anther which contributes to the male reproductive process of the plant. All the stamens do not bear fertile anthers.

Carpels

The carpel is the fourth whorl of the flower present in the centre. The carpels contain the pistil, the female reproductive part of the flower. It comprises the ovary, style, and stigma. The egg or the ovule is present in the ovary.

Functions of a Flower

1. Gametophytes develop in the flowers.
2. The flowers can produce diaspores without fertilization.
3. After fertilization, the ovary of the flower develops into a fruit containing a seed.
4. The most important function of flowers is reproduction. They help in the union of male and female gametes.
5. Flowers provide nectar to certain birds and insects, which in turn help in the transfer of pollen from one flower to the other.
6. Flowers may promote selfing, i.e., the union of sperms and eggs from the same flower, or cross-fertilization, i.e., the union of sperms and eggs from different flowers.