Plant Diversity II The Evolution of Seed Plants Test 3 New Characteristics of Seed Plants No longer require water for reproduction Gametophyte greatly reduced o Female gametophyte is an ovule o Male gametophyte is pollen Seed replace spores Heterosporous o 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 The gametophyte is no longer independent Two types of spores are seen in the seed plants They are heterosporous Megaspores o Gives rise to the female gametophyte An ovule containing an egg The outer layer of the ovule is the integument and the tissue of the ovule is diploid Microspores o Gives rise to the male gametophyte A pollen grain containing sperm o Microspores develop into pollen grains which can be dispersed by winds or animals eliminating the need for water in fertilization o A pollen grain can give rise to a pollen tube that allows for passage of sperm into the female gametophyte The seed develops from the ovule The integuments becomes the seed coat The zygote becomes the embryo The seed also contains tissue that acts as food for the new plant The seeded vascular plants can be divided into two major groups Non flowering Plants Gymnosperms o Coniferophytes The most successful because of their ability to live under a wide variety of conditions Evergreens including pine fir spruce cypress redwood and cedar o Cycadophytes o Ginkgophytes Have lag cones and palm like leaves Thrived during the Mesozoic era dinosaurs The only living species today is the Ginkgo biloba The fleshy seeds smell rancid as they decay It tolerates air pollution well o Gnetophytes Some are tropical others live in deserts Three genera Gnetum Ephedra welwitschia is no outer covering the female gametophyte o The seeds are referred to as naked seeds meaning that there o The stored food in the seed is haploid and arose directly from o Life cycle shows two of the key characteristics of seed plants Pollen Dominant Sporophyte Flowering Plants Angiosperms o The seeds have additional covering which is the fruit o The stored food is triploid and arises from a combination of female and male gametophytes o Make up the majority of modern land plants o Main characteristics Flowers Specialized shoot with modified leaves which are specific for sexual reproduction Complete Flowers Main Parts o Sepals Modified leaves in angiosperms that help enclose and protect a flower bud before it opens o Petals Modified leaves of a flowering Often colored to attract plant pollinators o Stamens The male reproductive part and consists of the filament stalk which holds the anther The anther contains the pollen grains o Carpel The female reproductive part and is a vase shaped structure made up of the stigma the style and the ovary Stigma is the top of the vase It s a sticky structure designed to catch the pollen Style is the neck of the vase The pollen must grown through the style to reach the egg Ovary is the bottom of the vase The ovary contains the ovules which become seeds The outer layer of the ovary becomes the fruit Seeds enclosed in fruit The main function of the fruit is to aid in seed dispersal Wind dispersal Mechanical dispersal Water dispersal Animal dispersal Broad leaves Advanced vascular tissue o Angiosperm pollination and Fertilization 1 Pollination starts when pollen from an anther lands on a 2 The pollen grain grows a tube down through the style stigma towards the ovary 3 The 2 sperm cells from the generative cell moves down the tube to the ovary where a double fertilization occurs Double Fertilization One sperm fuses with the egg cell to form a The other sperm fuses with polar nuclei in the primary endosperm cell making this triploid endosperm 3 sets of chromosomes zygote tissue o The angiosperms include Monocots Dicots Have one embryonic seed cotyledons Plants that have two embryonic seed leaves cotyledons Basil angiosperms ex water lilies Magnolids Eudicots Monocots Dicots Flower Structure Arranged in groups of 3 Arranged in groups of 4 or 5 Leaves Narrow with parallel veins Wider with branching netlike veins Vascular Tissue Scattered vascular bundles Ring of vascular bundles Roots Pollen Seed Many smaller roots One main taproot Single opening One cotyledon Three openings Two cotyledons The plant embryo contains the cotyledons seed leaves The similarities in the overall seed structure for Flowering and Nonflowering groups includes Embryo Stored food Seed coat Flower Anatomy Leaf Anatomy Plant Growth Overview Plant Structure Growth and Development Test 3 The basic design of land plants has two parts root system and the shoot system Root System The root is an organ that o Anchors the vascular plant o Absorbs mineral and water o Stores organic nutrients As a seed begins to grow the first root is the primary root In monocots this primary root is replaced by a fibrous root system composed of many roots about equal size In dicots the primary roots turn into the taproot system which has one main root that had lateral roots branch off The epidermis of the root is very thin and has no waxy cuticle In addition the epidermis forms roots hairs to increase the surface area These characteristics make the root very permeable to water The Shoot System As the shoot of a plant grows ar the apical bud it gives rise to different specialized tissues o Stems o Buds o Leaves o Flowers All of the shoot structures come from small groups of cells which are left behind by the apical bud o These groups of cells form leaf primordia leaf producing group and axillary buds branch producing group o These groups of cells are clustered at sites of nodes and are usually distributed at regular intervals along the stem These intervals are known as internodes the space between two nodes on the same side of the stem The formation of branches from lateral buds is triggered by hormones or lack of certain hormones o Leaves Leaves of a plant have two main parts the blade and the petiole the leaf stem Plants have three main tissue systems o Dermal Tissue System Outside covering from the protoderm Two tissues make up the dermal tissue system Epidermal tissue Forms the epidermis skin that covers the outside of the plant o Made up of thin walled cell with a waxy cuticle Periderm Can replace the epidermis in older woody stems branches and trunks o Made up of thick
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