1 NOTES FOR BIOLOGY 1202 DR STEVEN POMARICO INSTRUCTOR CHAPTER 30 Plant Diversity II The evolution of seed plants The next groups of land plants to evolve were the seeds plants The new characteristics that showed up with this group are No longer require water for reproduction Gametophyte greatly reduced Female gametophyte is an ovule Male gametophyte is pollen Seeds replace spores Heterosporous two types of spores Male and Female The ability of pollen to be dispersed by wind or animals allows the seeded vascular plants to break their ties to water Gametophytes of seed plants develop within the walls of spores retained within tissues of the parent sporophyte So the gametophyte is no longer independent Two types of spores are seen in the seed plants They are heterosporous Megaspores gives rise to the female gametophyte Microspores gives rise to the male gametophyte The two different gametophytes produce two types of gametes female gametophyte is an ovule containing an egg cell male gametophyte is a pollen grain containing sperm The outer layer of the ovule is the integument and the tissue of the ovule is diploid see fig 30 3 Microspores develop into pollen grains which can be dispersed by wind or animals eliminating the need for water in fertilization A pollen grain can give rise to a pollen tube that allows for passage of sperm into the female gametophyte 2 The seed develops from the ovule The integuments become the seed coat The zygote becomes the embryo The seed also contain tissue that acts as food for the new plant The seeded vascular plants can be divided into two major groups Nonflowering Plants Gymnosperms Flowering Plants Angiosperms In addition to the difference of flower production these major groups show differences in production of seeds The seeds of the gymnosperm are referred to as naked seeds meaning there is no extra outer covering The seeds of the Angiosperms have an additional covering which is the fruit The overall seed structure is similar for both groups see figs 30 6 and 30 7 with Embryo Stored food Seed coat In the gymnosperm the stored food in the seed is haploid and arose directly from the female gametophyte In the angiosperm the stored food is triploid and arises from a combination of male and female gametophyte material The gymnosperms include see fig 30 5 Coniferophytes Evergreens including Pine Fir Spruce Cypress Redwood and Cedar Cycadophytes most dominate in hayday Ginkgophytes 1 left Gnetophytes arid climate Of these four the Conifers are currently the most successful because of their ability to live under a wide variety of conditions including very harsh conditions The life cycle of the gymnosperms show two of the key characteristics of seed plants Pollen Dominant Sporophyte 3 The angiosperms make up the vast majority of modern land plants and have more than 250 000 species Flowers are specialized shoots with modified leaves which are specific for sexual reproduction The main characteristics include Flowers Seeds enclosed in a fruit see fig 30 8 Broad leaves Advanced vascular tissue Complete flowers have 4 main parts see fig 30 7 Sepals Petals Stamens Carpel The stamens are the male reproductive part and consist of the filament or stalk which hold the anther The anther contains the pollen grains male gametophyte The carpel is the female reproductive part and is a vase shaped structure made up of the stigma the style and the ovary The stigma is the top of the vase It is a sticky structure designed to catch the pollen The style is the neck of the vase The pollen must grow through the style to reach the egg The ovary is the bottom of the vase The ovary contains the ovules which become seeds The outer layers of the ovary become the fruit The main function of the fruit is to aid in seed dispersal see fig 30 9 wind dispersal mechanical dispersal water dispersal animal dispersal Angiosperm Pollination and Fertilization see fig 30 10 1 Pollination starts when pollen from an anther lands on a stigma 2 The pollen grain grow a tube down through the style towards the ovary 3 The 2 sperm cells from the generative cell move down the tube to the ovary where a Double Fertilization double fertilization occurs One sperm fuses with the egg cell to form the zygote The other sperm fuses with the polar nuclei in the primary endosperm cell making this triploid endosperm 3 sets of chromosomes tissue 4 The angiosperms include Basil angiosperms including water lilies Magnolids Monocots including grasses grains orchids and palms Eudicots sometime just called dicots For the most abundant angiosperms monocots and dicots there are characteristics which distinguish the two groups see fig 30 13 Flower structure Leaves Vascular tissue Roots Pollen Seed MONOCOTS arranged in group of three narrow with parallel veins scattered vascular bundles Many smaller roots Single opening One cotyledon DICOTS arranged in groups of four or five wider with branching netlike veins Ring of vascular bundles One main taproot Three openings Two cotyledons The plant embryo contains the cotyledons seed leaves see figs 30 6 and 30 10 In dicots there are 2 cotyledons in the embryo and monocots have only 1 cotyledon NOTES FOR BIOLOGY 1202 DR STEVEN POMARICO INSTRUCTOR CHAPTER 35 Plant Structure Growth and Development The basic design of land plants has two parts see fig 35 2 Root System Shoot System THE ROOT SYSTEM The root is an organ that anchors the vascular plant absorbs minerals and water stores organic nutrients 5 As a seed begins to grow the first root to emerge is the primary root see fig 35 3 In monocots this primary root is replaced by a fibrous root system composed of many roots of about equal size In dicots the primary roots turn into the taproot system which has one main root that lateral roots branch off The epidermis of the root is very thin and has no waxy cuticle In addition the epidermis forms root hairs see fig 35 3 to increase the surface area These characteristics make the root very permeable to water As the shoot of a plant grows at the apical bud it gives rise to different specialized tissues see fig 35 2 THE SHOOT SYSTEM Stems Buds Leaves Flowers All of shoot structures come from small groups of cells which are left behind by the apical bud These groups of cells form leaf primordia leaf producing group and axillary buds branch producing group The cell groups are clustered at sites called nodes and are usually distributed at regular intervals along the stem These intervals are known
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