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UNIT 6 Chapter 29: Plant Diversity I Chapter 30: Plant Diversity II Chapter 31: Fungi Chapter 35: Plant Structure & Growth Types of Land Plants Plants are: multicellular, eukaryotic, photosynthetic autotrophs Four MAIN groups of land plants exist: – Bryophytes: seedless, non-vascular – Pteridophytes: seedless, vascular – Gymnosperms: seeded, non-flowering – Angiosperms: seeded, flowering Vascular plants possess vessels (tubes) for transport of water and nutrients Features of Land Plants Main characteristics of the four groups of land plants: – Meristems Regions located at specific places from which new growth occurs – Apical, lateral – Multicellular embryos dependent on the parent plant Embryo is retained by parent; provides nutrients – Alternation of generations Two multicellular body forms alternate – Sporophyte: 2n, produces n spores by meiosis – Gametophyte: n, come together to form 2n zygote – Sporangia that produce spores Organs on the sporophyte that produce spores – Megasporangia: produce megaspores, becomes female gametophyte = produces egg – Microsporangia: produces microspores, becomes male gametophyte = produces sperm Spores will be released into air – Gametangia that produce gametes Organs on gametophyte that produce gametes – Archegonium: female gametangium produces a single haploid egg – Antheridia: male gametangia that produce many haploid sperm Other Features of Land Plants Many land plants possess a cuticle, a waxy layer on leaves to prevent water loss and infection Stomata, present mostly on the leaves allow for gas exchange and evaporation of water Vascular tissue transports water and nutrients (except bryophytes) – Xylem: transport of water and nutrients from roots Xylem is “dead” at maturity – only cell wall remains – Phloem: distribution of sugars, amino acids and other organic molecules Phloem is living tissue END Seeds A seed is a sporophyte embryo with its own food supply in a protective coat – Seed plants (gymnosperms and angiosperms) retain their spores Microspores develop into pollen – Carried off by wind or animals – Pollen carry sperm (1 or 2) to ultimately pollinate an egg Sperm are unflagellated Gymnosperms Modern gymnosperms appeared ~350mya Gymnosperms reflect 3 major changes in the evolution of plants – Increasing dominance of the sporophyte – Seeds resistant enough for dispersal – Pollen Conifers are the most common group of gymnosperms – Most have male and female cones on the same plant Smaller pollen cones produce microspores which develop into male gametophytes = pollen Larger ovulate cones make megaspores that develop into female gametophytes – Seeds typically dispersed by wind Most conifers are evergreen (vs. deciduous) and photosynthesize all year Needles are modified leaves adapted to dry conditions – Most have thick cuticles Most lumber and paper comes from conifers (xylem tissue) Conifers are among the oldest and largest organisms on earth Angiosperms Angiosperms have existed for ~130my – Categorized into two groups: monocots and dicots – ~250,000 known species The flower is the most significant evolutionary adaptation found in angiosperms – Reproductive structure Animals (esp. insects) often used to transfer pollen Angiosperms – The Flower Flowers are modified shoots with four types of modified leaves called whorls – Sepals, petals, stamens, carpels Female – carpel Male – stamen Angiosperms – The Fruit A fruit is a mature ovary – After fertilization, ovary wall thickens to form fruit – Protect dormant seeds and aid in dispersal Various modifications exist to aid in dispersal – Ex. Dandelions and maples use wind – Many angiosperms use animals for dispersal Edible fruits eaten and passed unharmed (along with fertilizer) Three main fruit types exist Plants & Humans All animals ultimately depend on plants, either for oxygen or for food Angiosperms provide virtually all of our food (~12 species) – Fruits, vegetables, grasses (corn, wheat, rice) Diversity in plants is a non-renewable resource – Human growth vs. plants Many plant (and animal) species go extinct as forests are cut down for agriculture Ethical concerns are not the only issue – Food, building materials, medicines Only about 2% of the 250,000 known plant species have been studied – More than 25% of prescription drugs are isolated from plants END Fungi Fungi are (usually) multicellular, eukaryotic, non-vascular, heterotrophic and possess a cell wall made of chitin Acquire nutrients by secreting exoenzymes and absorbing nutrients Act as decomposers, mutualistic symbionts and parasites Mycorrhizae are mutualistic associations between plant roots and fungi Fungus increases surface area for absorption by plant roots Fungus provides minerals from soil to plant; plant provides organic nutrients Almost all vascular plants have a mycorrhizae Plant growth is often stunted without mycorrhizae END Plant Anatomy Plants have three basic organs: roots, shoots and leaves Angiosperms have most features in common, but a few major features distinguish the monocots from the dicots A basic plant Plant Tissue Systems There are three main types of tissues found in plants: ground, dermal and vascular All types are found throughout the plant Dermal Covers outer surface of plant Extends to create root hairs Secretes cuticle Vascular (xylem) Tracheids are individual units of xylem Vascular (phloem) Organic material moves through chains of cells called sieve-tube members Ground Neither dermal nor vascular Photosynthesis, storage and support The three tissue types are made up of three major cell types Parenchyma: (living) sieve-tube members, photosynthesis, storage Collenchyma: (living) support young parts of plant Sclerenchyma: (dead) thick cell walls, tracheids, support & transport Growth & Development Most plants grow and develop throughout their lifetime – indeterminate growth Growth: increase in mass due to cell division Development: changes that elaborate an organism’s body Plant life cycles vary based on when they are capable of reproduction Germination flowering seed production death Annual, biennial, perennial Meristems are regions of embryonic cells Apical: increase in plant’s length/height – primary growth Lateral: increase in plant’s width – secondary growth Leaf Anatomy Leaf epidermis comprised of tightly packed cells Stomata: tiny pores found in the epidermis flanked by guard cells Water pressure in guard cells control stomata opening/closing Mesophyll is ground tissue sandwiched in between two epidermal layers O2 and CO2 circulate in the spaces in the parenchyma Vascular tissue is continuous with that of the stem END