Plant Diversity and Structure

Kingdom Plantae Eukaryotic Multicellular Mostly terrestrial  Increased sunlight, more CO 2, nutrient rich soils Cell walls of cellulose (a polysaccharide) Mostly autotrophic/photosynthetic  Some parasitic species Believed to have evolved from green algae known as charophytes more than 500 million years ago

Plant Reproduction – Alternation of Generations Plant life cycle consists two multicellular stages:  Gametophyte – haploid stage that produces gametes Archegonia – female sex organ that produces eggs Antheridia – male sex organ that produces sperm  Sporophyte – diploid stage that produces spores (the dominant stage in most plants  what you see when you look at a plant) Megaspores – develop into female gametophyte Microspores – develop into male gametophyte

Alternation of Generations Gametophyte stage (1n) – gametes produced Fertilization occurs to form diploid zygote  mitosis  sporophyte (2n) Sporophyte produces spores by meiosis Spores undergo mitosis to form gametophyte

Plant Phyla Four main groups:  Bryophytes  Pteridophytes  Gymnosperms  Angiosperms

Bryophytes (mosses) Includes mosses, liverworts, and hornworts Nonvascular (no xylem or phloem tissue) Small in size and grow close to ground; anchored by rhizoids Require water for fertilization (release sperm into water) Gametophytes dominant stage of life cycle

Pteridophytes (ferns) Includes club mosses, quillworts, ferns, horsetails, whisk ferns Vascular, but seedless Have true roots and leaves Sporophyte is the dominant stage Still require water for fertilization

Gymnosperms (pines and conifers) Vascular “naked” seeds Produce pollen grains Have modified leaves that form cones Includes ginkgo, cycads, gnetophyta, and conifers (most common)

Angiosperms (flowering plants) 90% all plant species – most successful Vascular Have seed/s that develop from ovules within protective ovaries Produce pollen Also have:  flowers – complex reproductive structures  fruits – mature ovaries of plants

Flower Parts Sepals – enclose bud Petals – attraction Stamen – male part  Filament  Anther – pollen Carpel/Pistil – female part  Stigma - pollen sticks  Style  Ovary – houses ovules

Angiosperms Traditionally divided into monocots and dicots  Mono – one cotyledon  Di – two cotyledons

Advantages of Seed Plants Seeds – embryo and food in protective coat Reduced gametophytes within cones or flowers Heterospory – produce two spore types  Megaspores and microspores Ovules and production of eggs  Ovules – in the ovary and develop into the seed  Protects egg and zygote

Pollen and sperm production  Pollen grain – contains two sperm nuclei and has waterproof coating  Eliminates need for water for fertilization Variation of seed dispersal  Seeds protected by fruits  May be kite or propeller like – wind dispersal  May be modified as burrs – animal dispersal  May be eaten and digested – animal dispersal

Three Basic Plant Organs Roots  Anchor the plant  Absorb water and minerals  Store sugars and starches (food) Stems  Structure  Display leaves  transport Leaves  Photosynthesis  Gas exchange

Four major tissue types: Dermal – single outer layer (epidermis)  Forms cuticle – a waxy layer that protects and holds in water Vascular – transports material (vascular bundles/veins)  Xylem – transports water from roots to shoots; consists of tracheids and vessel elements  Phloem – transports sugars from leaves to rest of plant; consists of sieve tube elements and companion cells Ground – anything else  Pith – inside vascular tissue  Cortex – outside vascular tissue

Xylem and Phloem

Meristematic - embryonic tissue for growth (mitosis)  Apical meristems – tips of roots and shoots Allow plant to grow in length  PRIMARY GROWTH Apical dominance – plant concentrates resources on growing taller towards light  Axillary bud growth is stimulated only when terminal bud is removed Protoderm – gives rise to new epidermis Procambium – gives rise to primary vascular tissue  Lateral meristems – result in growth which thickens shoots and roots Grow in width  SECONDARY GROWTH Includes vascular cambium – produces new secondary vascular tissue

Three major types of cells Parenchyma – most abundant and least specialized  Have thin and flexible primary walls  Perform most of plant’s metabolism Collenchyma – grouped in cylinders and help support growing plant  Thicker primary cells walls Sclerenchyma – supporting elements  Thick secondary walls strengthened with lignin  Found in mature plant parts no longer growing

Other important parts - Roots Root hairs - increase surface area for absorption Root cap – tough layer of cells that protect apical meristem

Leaves Blades – thin, flattened sections Petiole – think stalks that attach leaf to stem Mesophyll – specialized ground tissue where most photosynthesis takes place Stomata – tiny openings on the underside of leaves  Allow for gas exchange  Surrounded by guard cells that control opening and closing  Also site of water loss - transpiration

Stems  Nodes – where leaves attach  Internodes – regions between nodes  Buds – undeveloped tissue that can produce new stems and leaves  May develop woody tissue (wood is the layers of xylem)

 Phytomer - repetitive units of growth that occur along the plant consisting of a leaf, a section of the stem, and a lateral bud