1 EXERCISE # 9 FLOWER, POLLEN GRAIN AND OVULE I. IntroductionFlower is the organ for sexual reproduction in the most evolutionary advanced plants on earth, the flowering plants. Sexual reproduction, which involves the union of gametes, ensures genetic variation among offspring and makes them better suited to their changing environment. Such gametes, sperm and egg cells, are contained within the pollen grain and ovule of the flower, respectively. Since the plant is immobile and rooted, it is necessary for some external agents (wind, water, animals or the plant itself) to bring the gametes together, particularly for plants not undergoing self-fertilization. The flowers show remarkable variations in form, color, smell, nectar content and other features that facilitate this transfer of pollen grains from one flower to another. Likewise, the features of pollen grains and ovule correspondingly vary with the flower types and pollination vectors. II. ObjectivesAt the end of this exercise, the student is expected to be able to 1.Identify the parts of a flower and define terms related to floral variations and characteristics. 2.Predict the flower’s pollination vector based on the floral characteristics. 3.Describe the pollen grain and ovule in terms of structure and development. III. MaterialsEquipment/apparatusCompound light microscope Dissecting microscope or magnifying lens Blade, glass slides, cover slips Plant specimens/prepared slidesFresh gumamela flowers (one per group) Prepared slides of Lily ovary and anther Five selected flowers in the campus (monocot and dicot combined) IV. ProcedureA.Flowers A.1. Basic Parts of a Flower Examine the basic parts of a flower using the gumamela flower as model. A flower is a modified shootwith a compressed axis, bearing a series of floral leaves or whorls that have been variously modified into sepal, petal, stamen and pistil. The point of attachment of these floral whorls is the receptacle.The flower is attached to the stem by the peduncle.
2 a) Sepals(collective term: calyx) constitute the outermost and lowest whorl that protects the flower bud and bases of the expanded whorls. They may be fused or free, green and leaf-like or composed of petal-like tissues. Which describe the gumamela sepals? The small leaf outgrowths below the sepals are the epicalyx, which function for additional photosynthesis. b) Petals(collective term: corolla) are modified leaves usually functioning as visually conspicuous "signposts" which serve to attract specific pollinators. They occur in various sizes, shapes and smell, and may be dull to brightly colored, fused, free or even absent. In the gumamela flower, make a shallow longitudinal slit through the sepals and petals using a scalpel to examine the petal attachment. Are the gumamela petals free or fused? Calyx and corolla taken as one is called perianth, from Greek peri‘around’+ anthos‘flower.’petals and sepals are strikingly similar in color and texture, they are termed tepalsc) Stamens(collective term: androecium) are composed of sac-like anthersand their supporting filaments. The number of stamens in a flower depends on the species. Sometimes, the filaments are attached to the petals; sometimes they are free. In the gumamela, the filaments fuse at their bases to form the staminal tubed) Pistil(collective term: gynoecium) is composed of one or several carpels which fuse to form an essentially closed case that contains the ovules. The three regions of the pistil (from the base up) are the ovary, style and stigma. The ovarycontains one or more ovules. The styleis a stalked structure atop the ovary that elevates into a sticky knob called stigmaIn the gumamela, make a shallow slit from the base of the staminal tube to its tip. Carefully open and locate the thread-like style inside the staminal tube. Five stigmas project from the distal end of the style. At its proximal end is the oblong-shaped ovary. Make a simple sketch of the longitudinally dissected gumamela flower showing its receptacle and the When . . .
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