Flower

I. INTRODUCTION OF FLOWER Flower, reproductive organ of most seed-bearing plants. Flowers carry out the multiple roles of sexual reproduction, seed development, and fruit production. Many plants produce highly visible flowers that have a distinctive size, color, or fragrance. Almost everyone is familiar with beautiful flowers such as the blossoms of roses, orchids, and tulips. But many plants—including oaks, beeches, maples, and grasses—have small, green or gray flowers that typically go unnoticed. Iris Triggered mainly by the shortening periods of darkness during spring, flower buds open to display brightly colored petals that attract insects seeking nectar. Once a flower has been pollinated, its petals shrivel and drop off. Whether eye-catching or inconspicuous, all flowers produce the male or female sex cells required for sexual reproduction. Flowers are also the site of fertilization, which is the union of a male and female sex cell to produce a fertilized egg. The fertilized egg then develops into an embryonic (immature) plant, which forms part of the developing seed. Neighboring structures of the flower enclose the seed and mature into a fruit.

II.PARTS OF A FLOWER All flowers share several basic features. A flower begins growth at the end of a specialized branch known as a peduncle or pedicel. This branch enlarges at its tip to form the receptacle, to which other plant parts attach. Sepals, protective coverings that close over the bud before it blooms, are the outermost flower parts. One step inward lie the petals, which use both coloration and scent-producing glands to attract pollinators. Inside the petals are the flower's sexual organs, the stamens and pistil. Each stamen, the pollen producing part of the flower, includes an anther and a filament. At the center of the flower is the pistil, composed of a stigma, a style, and an ovary. Within the ovary is a small cavity that contains the ovule, an egg-shaped structure that, when fertilized, eventually becomes a seed Flowers typically are composed of four parts, or whorls, arranged in concentric rings attached to the tip of the stem. From innermost to outermost, these whorls are the (1) pistil, (2) stamens, (3) petals, and (4) sepals.

III SEXUAL REPRODUCTION Pollination Flowering plants may use wind, insects, bats, mammals, or birds to facilitate the transfer of pollen from the stamen, or male portion of the flower, to the stigma, or female portion. Many species of plants have evolved closely with certain animals to ensure successful transfer of pollen. For example, many species of rain forest plants can only be pollinated by one particular species of insect, bird, or bat. The tiny male “flowers” are located at the ends of the small branchlets, where the wind can easily pick up and distribute their pollen. Butterfly Pollinating a Flower Many species of butterflies eat plant nectar. When these butterflies land on a series of flowers in search of food, they brush their bodies against both male and female floral organs, inadvertently transferring pollen from one flower to another. Sexual reproduction mixes the hereditary material from two parents, creating a population of genetically diverse offspring. Such a population

can better withstand environmental changes. Unlike animals, flowers cannot move from place to place, yet sexual reproduction requires the union of the egg from one parent with the sperm from another parent. Flowers overcome their lack of mobility through the all-important process of pollination. Pollination occurs in several ways. In most flowers pollinated by insects and other animals, the pollen escapes through pores in the anthers. As pollinators forage for food, the pollen sticks to their body and then rubs off on the flower's stigma, or on the stigma of the next flower they visit. In plants that rely on wind for pollination, the anthers burst open, releasing a cloud of yellow, powdery pollen that drifts to other flowers. In a few aquatic plants, pollen is released into the water, where it floats to other flowers.

EVOLUTION OF FLOWERS Tall Buttercup although buttercups, such as Ranunculus acris pictured here, abound in pastures, grazing cows avoid them. Ingesting the shiny, double blossom irritates the mucous membranes of the digestive tract. Dried buttercup blossoms, however, are harmless inclusions in hay. Because of their resemblance to their fossil ancestors, buttercups are thought to be among the oldest groups of plants living today. Flowering plants are thought to have evolved around 135 million years ago from cone-bearing gymnosperms. Scientists had long proposed that the first flower most likely resembled today’s magnolias or water lilies, two types of flowers that lack some of the specialized structures found in most modern flowers. But in the late 1990s scientists compared the genetic material deoxyribonucleic acid (DNA) of different plants to determine their evolutionary relationships.

Submitted by: ARPANDEEP KAUR (Science Mistress) Govt. Sr. Sec. School (B) Goraya (Jalandhar)

Bibliography 1. Text book of Punjab school education Used for all the Documentation. 2. For pictures of Flowers inter served (google.com and yahoo.com)