Flower PDF - Structure of a Bisexual Flower

Downloaded from https://www.studiestoday.com 4 Unit-2 THE FLOWER...

Downloaded from https://www.studiestoday.com 4 Unit-2 THE FLOWER Flowering Plants Syllabus: Flower : Structure of a bisexual flower, functions of various parts. A brief introduction to complete and incomplete flowers. Essential and non-essential whorls of a bisexual flower; their various parts and functions. Inflorescence and placentation (meaning only). (Charts or actual specimens may be used to help enhance clarity of concepts). You have already learnt that reproduction is the projecting out and each usually ending in a most important function of any living organism for bilobed tip. These are stamens (collectively the survival of the species. In flowering plants this named androecium). Each stamen consists of function is performed by the flower. The flower is threadlike filament and bilobed anther. usually the most beautiful and conspicuous part of a 4. Fourth whorl (female parts) (₽ = symbol for plant. female) (centrally located pistil that may be 4.1 STRUCTURE OF A BISEXUAL FLOWER formed of a single female unit (carpel) or of several (FIG. 4.1) fused carpels (collectively called gynoecium). Flower is a specialized shoot in which the leaves are Each carpel consists of a basal ovary, a middle style and an uppermost stigma. modified into floral structures. 4.1.1 COMPLETE AND INCOMPLETE FLOWERS: First of all, there is the stalk (pedicel) which supports the flower. Some flowers may be without A complete (or perfect) flower is one which stalk (sessile). The tip of the flower stalk may be contains all the four floral structures. If one or more expanded to form a cup-shaped receptacles thalamus. sets of floral structures are missing, the flower is The floral parts are borne on the thalamus in called incomplete (or imperfect). four whorls. Essential (reproductive) and non-essential (non- 1. First whorl - green sepals (collectively called reproductive) parts of a flower. The essential parts calyx). of a flower are those that are directly concerned 2. Second whorl - large brightly coloured petals with reproduction. These parts consist of the stamens (male parts) and the carpels (female parts). (collectively called corolla). The non-essential (accessory) parts are simply 3. Third whorl (male parts) (o = symbol for male) the helping parts which either protect the reproductive - long thread-like processes somewhat parts of the flower or make the flower attractive for pollination. These parts include the sepals and petals. STIGMA In some cases the petals and sepals are undifferentiated ANTHER together called perianth. When the perianth is non- - STYLE| (3) FILAMENT. green it is described as petaloid. (4) When the perianth is green like the sepals, it is OVARY PETAL (2) OVULE described as sepaloid perianth. Bracts—When a flower arises in the axil of a SEPAL RECEPTACLE leaf-like structure, this structure is known as bract. (1) STALK Bracts may be green like ordinary leaves or at times Fig. 4.1 Generalized arrangement of parts of a bisexual flower they are coloured. The large and colourful bract of Downloaded from https:// www.studiestoday.com  Downloaded from https://www.studiestoday.com Bougainvillea (Fig 4.2) is easily mistaken for petal. Neuter flower - A flower in which both male The actual flower in this case is small, somewhat and female reproductive organs are lacking. Example: cylindrical and attached on the inner side of the bract. Ray florets of sunflower. FLOWER 4.2 GENERAL DESCRIPTION OF THE FLORAL PARTS (a) Calyx (sepals). Usually there are five sepals. Sometimes they may be less or in a few cases even BRACT more. The sepals may be free polysepalous or fused gamosepalous (Fig 4.4). Sometimes, as in Hibiscus Fig. 4.2 Bougainvillea. Large, coloured bracts (shoe-flower) there may be a second series of sepals bear the flowers called episepals, collectively called epicalyx. When Nectaries : Most flowers produce a sweet the flower opens the sepals may fall off or persist. fragrant liquid called nectar. Groups of nectar- Sepals are usually green but in some cases they are secreting cells, nectaries are situated usually at the brightly coloured (called petaloid) as in Gul Mohur base of the pistil or on the bases of the petals. The (flame of the forest) where they are red. nectar attracts insects like honeybees, for cross pollination. In some cases nectaries are very prominent as in Nasturtium (Fig 4.3) PETAL (b) (a) (c) Polysepalous Gamosepalous - SEPAL Fig. 4.4 Calyx - free (a) and fused (b and c) types of sepals The sepals protect the young flower bud and when green they also perform photosynthesis. STALK NECTARY (b) Corolla (petals). The petals are generally arranged in a single whorl but sometimes there may Fig. 4.3 Nasturtium. A flower cut medially to show the nectary containing a clear liquid (the nectar) at the bottom be a double whorl (e.g. Poppy) or in a spiral (e.g. Water lily). They may be free polypetalous or united 4.1.2 SEXUALITY IN FLOWERS gamopetalous forming a tube (Fig. 4.5). Male, female and bisexual flowers. The anthers of the stamens produce pollen which forms the male cells (male gametes). The ovary of the carpel bears the ovule which encloses the egg cell (female gamete). The stamens and the carpels are the male C Free Tubular Funnel shaped and female parts of the flower respectively. — A flower which contains both stamens and carpels Fig. 4.5 Kinds of corolla. A-Free petals, B-Petals fused in a tubular form C-Petals fused, somewhat funnel shaped is called bisexual or hermaphrodite or just a perfect flower. The petals attract insects for pollination. They — A flower which has only one of these parts, that is, also protect stamens and pistils especially when having only the stamens or only the carpels is the petals form a tube. called unisexual or incomplete (imperfect) flower, (c) Androecium (stamens). The number of e.g. papaya and palm. stamens in different flowers may vary from a few to — A unisexual flower which contains only the stamens a large number. Each stamen consist of: a long is called the male or staminate flower. filament and an anther attached to its extremity. The - A flower which contains only the carpels is called anther is usually two lobed. Each lobe has two pollen the female or the pistillate flower. sacs [four sacs in all (Fig. 4.6A)]. Within the pollen 30 Downloaded from https:// www.studiestoday.com  Downloaded from https:// www.studiestoday.com sacs are contained pollen grains. When fully matured (d) Gynoecium (carpels). Gynoecium is also the pollen sacs rupture to liberate pollen grains. The known as pistil. It is composed of one or more pollen grains are generally powdery particles of carpels. Each carpel consists of three parts-stigma, different shapes and sizes (Fig. 4.6B). style and ovary. Stigma is the terminal knob-like part, it may be POLLEN SAC — divided into two or more lobes and may assume a POLLEN GRAINS feathery appearance. The stigma is covered with hair or with glandular papillae. It serves as the landing place for pollen during pollination. Style is the tubular slender stalk which connects FILAMENT B the stigma to the ovary. Ovary is the swollen basal portion composed of Fig. 4.6 A-Pollen sacs contain pollen grains (diagrammatic). one or many carpels. The inner cavity of the ovary may B-Pollen grains from different plants show different be a single chamber or divided into several chambers shapes and sizes (locules) each containing a number of rounded bodies, In androecium, stamens may be free the ovules. The cushion or swollen region in the ovary (polyandrous) as in Petunia, or joined in different attaching the ovules to the wall of the ovary is called ways in single, double or several groups (Fig. 4.7): placenta. Sexuality in plants In most plants the flowers are bisexual. They have both male and female parts. In many plants the male and female flowers are separate. Such plants are of two types : (i) Monoecious plants (mono: one, oecium : house): Male and female flowers grow on the same plant e.g. maize, cucumber, pumpkin, etc. Monadelphous Diadelphous Polyadelphous Dioecious plants (di : two): Male flower (staminate) (Single group) (Two groups) (Several groups) (ii) and female flower (pistillate) grow on different plants Fig. 4.7 Cohesion (joining) of stamens. e.g. palm, papaya, etc. (i) Monadelphous : Stamens are united in one PROGRESS CHECK group by their filaments. Only anthers are free. e.g., china rose (staminal tube),cotton. 1. Mention if the following statements are true (T) or false (F) (ii) Diadelphous : The filaments are united in two (i) Flowers can be complete or incomplete. T/F bundles. e.g. pea (out of ten, nine stamens form (ii) A flower typically has six floral whorls. T/F a staminal tube while one is free). (iii) Bracts are usually green, but sometimes large and colourful. T/F (iii) Polyadelphous : The filaments are united in (iv) Nasturtium has nectaries. several groups. e.g. Bombax. T/F (v) Stamens and carpels are the male and female parts T/F How to remember the above three terms ? (vi) The prefix "gamo-" is used whenever any of the Mono -, Di - and Poly - respectively mean single, floral whorls are fused T/F two and several. (vii) Stigma may be simple or divided into two or more Adelphous literally means "group of brothers", here lobes. T/F referring to the part from which the anthers grow out (viii) Papaya is monoecious plant. T/F in bundles. Thus the bundle of anthers arising from a 4.3 INFLORESCENCE AND PLACENTATION single part (monadelphous or monodelphous), the bundles from two parts (diadelphous) and from Inflorescence is the mode of arrangement of several parts (polyadelphous). flowers on the axis of the plant 31 Downloaded from https://www.studiestoday.com  The flowers may onlonged en several attres: my studiestod aro.cog growing out from the axils of ways in different plants, this manner of arrangement different leaves reaching the is termed inflorescence. same level making a cluster. The axis is laterally flattened making a disc as in sunflower. The youngest flowers are in the centre and oldest in the periphery. singly either at the apex of in the axils of Placentation is the manner in which the ovules the main stem or at the the leaves. are arranged/attached to the wall of the ovary. terminal apex of the lateral branches. Ovules turn into seeds in the mature fruit (transformed ovary). Their different arrangements can Placenta : Tissue that attaches the ovule to the be seen in fruits such as those of pea, tomato, mango, wall of the ovary. lotus, etc. POINTS TO REMEMBER Flower is a reproductive organ. > Essential parts of a flower include the stamens (male parts) and the carpels (female parts). > Sepals protect the bud, petals attract insects, stamens produce pollen grains, carpel receives pollen and its ovary becomes the fruit containing seeds (ovules). > Essential parts of a flower are the reproductive parts (stamens and carpels) and non-essential ones the non- reproductive parts (petals and sepals). › Nectaries are common in most brightly coloured (insect-pollinated) flowers. > Sepals may be brightly coloured, these are then said to be petaloid. The pollen grains are fine powdery particles of different shapes. The manner of arrangement of flowers on the plant is termed inflorescence. REVIEW QUESTIONS A. MULTIPLE CHOICE TYPE 3. The part of the flower that gives rise to the fruit is 1. Bougainvillea flower is an example of (a) Sepals (b) Petals (c) Ovary (d) Stamens (a) incomplete flower 4. The part of the flower that gives rise to the seed is (b) having a large nectary (a) Ovary (b) Placenta (c) Ovule (d) Pollen grain (c) water pollination (d) large colourful bracts 5. The essential whorls of a flower are the 2. A flower is said to be complete when : (a) Calyx and corolla (a) It has the corolla and calyx (b) Stamen and ovary (b) It has the corolla and gynoecium (c) Calyx and epicalyx (c) It has the androecium and gynoecium (d) Androecium and gynoecium (d) It has all the four whorls. 32 Downloaded from https:// www.studiestoday.com  Downloaded from https:// www.studiestoday.com B. VERY SHORT ANSWER TYPE (b) What part of the flower do the names given above refer to ? 1. Match the parts in Column A with the flowers or parts of flower in Column B. 2. The figure given alongside represents generalised Column A Column B arrangement of the different parts of a bisexual (a) Polyadelphous flower. Name the parts numbered 1-10. (1) Polypetalous (b) Pollen grains (i1) Calyx, corolla (c) Free petals (iji) Nectar (d) Non-essential (iv) Bombax (e) Sweet fragrant fluid (v) Pollen sac C. SHORT ANSWER TYPE 1. Explain the following terms : -10 (a) Incomplete flower (b) Staminate flower (c) Pistillate flower (d) Bisexual flower 2. Distinguish between the following pairs : 3. Given below are two figures (A & B) of a certain part of a flower. Study the figures carefully and (a) Flower and inflorescence, answer the following questions: (b) Petals and petaloid sepals. (a) Which major organ of a flower does the figure 3. Where are the following structures/parts located and A represent ? What is the collective term what are their functions ? for this organ ? (a) Placenta (b) Thalamus (b) Are the contents of the pollen sacs in B male (c) Anther (d) Stigma or female ? Why are the following described as stated : (c) Can you state how the contents of the pollen (a) The androecium of pea flower is didelphous sacs would come out ? (b) Ray florets of sunflower as neuters (c) Salvia sepals as petaloid (d) China rose stamens as epipetaloid D. LONG ANSWER TYPE ANTHER POLLEN GRAINS 1. Name the different types of androecium found in flowers POLLEN SAC 2.Name the type of androecium found in ANTHER (a) China rose (b) Bombax (c) Pea FILAMENT в E. STRUCTURED/APPLICATION/SKILL 4. What are bracts ? State their function. TYPE 5. Explain the terms Monodelphous, Didelphous and 1. There is a flower in which you use the following Polydelphous. In each case name a flower possessing terms : Standard, wings and keel. such an androecium. (a) Name the flower 33 Downloaded from https://www.studiestoday.com