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NOTES FOR BIOLOGY 1202DR. STEVEN POMARICO, INSTRUCTORCHAPTER 30Plant Diversity II: The evolution of seed plantsThe next groups of land plants to evolve were the seeds plants. The new characteristics that showed upwith this group are:-No longer require water for reproduction-Gametophyte greatly reducedFemale gametophyte is an ovuleMale 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 theirties to water.Gametophytes of seed plants develop within the walls of spores retained within tissues of the parentsporophyte. 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 gametophyteMicrospores - gives rise to the male gametophyteThe two different gametophytes produce two types of gametesfemale gametophyte is an ovule containing an egg cellmale gametophyte is a pollen grain containing spermThe 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 needfor water in fertilizationA pollen grain can give rise to a pollen tube that allows for passage of sperm into the femalegametophyte.1The seed develops from the ovuleThe integuments become the seed coatThe 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 - GymnospermsFlowering Plants - AngiospermsIn addition to the difference of flower production, these major groups show differences in production ofseeds.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 coatIn the gymnosperm the stored food in the seed is haploid and arose directly from the femalegametophyte.In the angiosperm the stored food is triploid and arises from a combination of male and femalegametophyte material.The gymnosperms include (see fig 30.5):ConiferophytesEvergreens including Pine, Fir, Spruce, Cypress, Redwood and CedarCycadophytes- most dominate in haydayGinkgophytes- 1 left Gnetophytes- arid climateOf these four, the Conifers are currently the most successful because of their ability to live under a widevariety of conditions (including very harsh conditions).The life cycle of the gymnosperms show two of the key characteristics of seed plants:-Pollen-Dominant Sporophyte2The angiosperms make up the vast majority of modern land plants and have more than 250,000 species.The main characteristics include:-Flowers-Seeds enclosed in a fruit (see fig. 30.8)-Broad leaves-Advanced vascular tissueFlowers are specialized shoots with modified leaves which are specific for sexual reproductionComplete flowers have 4 main parts (see fig. 30.7)-Sepals-Petals-Stamens-CarpelThe 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 stigma2) The pollen grain grow a tube down through the style towards the ovary3) The 2 sperm cells from the generative cell move down the tube to the ovary where a3double fertilization occursDouble FertilizationOne 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) tissueThe angiosperms include:Basil angiosperms – including water liliesMagnolidsMonocots – including grasses, grains, orchids, and palmsEudicots – sometime just called dicotsFor the most abundant angiosperms (monocots and dicots) there are characteristics which distinguish thetwo groups (see fig. 30.13).MONOCOTS DICOTSFlower structure arranged in group of three arranged in groups of four or fiveLeaves narrow with parallel veins wider with branching netlike veinsVascular tissue scattered vascular bundles Ring of vascular bundlesRoots Many smaller roots One main taprootPollen Single opening Three openingsSeed One cotyledon Two cotyledonsThe 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 cotyledonNOTES FOR BIOLOGY 1202DR. STEVEN POMARICO, INSTRUCTORCHAPTER 35Plant Structure, Growth, and DevelopmentThe basic design of land plants has two parts (see fig 35.2):-Root System-Shoot SystemTHE ROOT SYSTEMThe root is an organ that4-anchors the vascular plant-absorbs minerals and water-stores organic nutrientsAs 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.THE SHOOT SYSTEMAs the shoot of a plant grows at the apical bud it gives rise to different specialized tissues (see fig 35.2):StemsBudsLeavesFlowersAll 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


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LSU BIOL 1202 - CHAPTER 30

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