[Biology Class Notes] on Flower Pdf for EXAM

The flower is the reproductive part of the plant. Flowers have had a deep connection with human beings since ancient times. Flowers express sorrow, grief, happiness, and celebration by human beings. The plant decides to form the flower before during the developmental stage itself. The various hormones and cells influence the shaping of the flower. The flower is the part of the plant which contains male and female pieces that interact with each other and reproduce to carry on the plant formation.

Few flowers are colorful and blooming with vibrant colors that attract different organisms that help in the process of pollination. 

Parts of a Flower

Flowers have four main components, namely sepals, petals, carpels, and stamens. A flower could be male, female, or both. If both stamen and carpel are present, it is a bisexual flower. If either stamen or carpel is present, it is called a unisexual flower. 

1. Peduncle: It is the stalk in which the flower attaches.

2. Receptacle: It is part of the flower present at the central base at which the stalk attaches.

3. Sepals: It is the outermost whorl of the flower. It is a leaf-like structure beneath the petals. The group of sepals is called a calyx. The primary function of the calyx is the protection of the flower in the bud stage.

4. Petals: It is the part of the flower that is vibrant and attracts pollinators. It is collectively known as the corolla.

5. Stamen: It is the male part of the flower which contains the pollen grains. It has two parts: Anther and Filament.

6. Carpels: It is the female part of the flower which contains the ovary. It has three parts: Stigma, Style, and Ovary.

The Vegetative Part of a Flower

It is the part of a flower that is not involved in the process of reproduction. It includes all the parts of the flower apart from the stamen and carpel.

1. Calyx: It is the outermost part of the flower and is called sepals. It protects the bulb in the bud stage and is present below the petals. It is tiny and green colored and it may be absent in a few flowers and, in a few, maybe similar to the leaves.

2. Corolla: It is the part of the flower that is bright and colorful. It is the modified part of the leaves which is grown mainly to attract different insects. It produces scent and nectar for the insects so that it transfers the pollen grains to other plants and helps in pollination. In a few plants, it may be pale and dull; such plants pollinate through abiotic means.

Reproductive Part of a Flower

Reproductive parts of the flowers are the part that performs sexual reproduction. Angiosperms are flowering plants and have two parts male and female.

1. Stamen: It is also called Androecium. It contains anther and filament. The filament is the long slender stalk that holds the anther. The anther is the part of the flower that contains anther sacs in its lobes called pollen grains. The pollen grains are the male gametes that interact with the female gamete to form the endosperm and the embryo.

2. Carpels: It is also called Gynoecium. If it contains a single pistil, it is called monocarpellary. If it includes many pistils, it is termed multicarpellary. The stigma, style, and ovary are the parts of the carpel. The stigma is the receptive surface that attaches the pollen; the style is the connection between the stigma and the ovary; the ovary is the central part of the plant where the process of double fertilization takes place.

Functions of a Flower

• The primary purpose of a flower is the process of reproduction as flowers are the reproductive parts of the plant. The ovary receives the pollen grain from pollinators and starts developing the embryo and endosperm inside the embryo sac of the ovary. The pollen grain forms by meiosis of microspore mother cells. The female gametophyte, i.e, the embryo sac is formed by the meiosis of megaspore mother cells where three cells degenerate and one cell forms to be the embryo sac.

• The flower forms the basis for the formation of seeds and fruit. After fertilization, the ovules form into seeds, the petals wear off, and the fruit begins to form from the flower.

• Flowers are vibrant and bright colored in many species which attract insects for pollination. In this case, flowers are cultivated and used by human beings for various occasions. Flowers have always been an essential part of religious rituals, weddings, funerals, social gatherings, expressing love, and many more. 

Pollination

Pollination is the transfer of the pollen grains from the male anther to the stigma of the female flower. Most of the flowers can have both male and female parts of the flower in the same flower; these are called bisexual flowers. If the bulb has only male or female roles, they are called unisexual flowers. However, if an individual plant has both a male flower and also a female flower, it is called a monoecious plant. If a particular plant only has male flowers in a plant or female flowers in a plant, it is called dioecious.

Types of Pollination

1. Autogamy: If the pollination takes place within the stigma and another of the same flower, it is called autogamy. There are two types of flowers in this case. Chasmogamous flowers are flowers that have exposed anthers and stigma. They also have a chance of cross-pollination. E.g., Viola, oxalis, hibiscus, beans. Cleistogamous flowers are flowers that do not expose their stigma and anther and hence, do not have any chance of cross-pollination. E.g., Groundnut, peas.

2. Geitonogamy: The transfer of pollen from the anther of one flower to the stigma of the other flower but it takes place in the same plant. It is similar to autogamy, as the pollen and ovary are genetic of the same plant. E.g., Maize.

3. Xenogamy: It is the transfer of pollen grains of a flower of one plant to the stigma of another plant. This type of pollination occurs most of the time in nature as it provides genetic variation in the species and the evolution of plants takes place.

Agents of Pollination

1. Abiotic Agents: These are agents like wind and water that transfer the pollen grains. Wind pollination is called anemophily where the pollen grains are light and non-sticky and produced in numbers. The anthers are well exposed, and the stigma has a downy surface to trap the pollen grains. E.g., Rice, wheat, corn, barley. Water pollination is called hydrophily where the pollen grains transfer through the water. It occurs mostly in monocotyledons, some bryophytes, and pteridophytes. E.g., Vallisneria and Hydrilla. Since they do not attract biotic pollinators, these flowers are not very attractive and vibrant.

2. Biotic Agents: These are the flowers that get pollinated utilizing insects, animals, and birds. Common pollinating agents are bees, ants, moths, butterflies, flies, beetles, wasps, sunbirds, and hummingbirds. Other agents like garden lizards, gecko lizards, lemurs, tree-dwelling rodents are pollinators. These flowers have vibrant and attractive flowers that produce a scent and nectar. Nectar is the animal reward for pollinators.