Plants

Plant Diversity About 280,000 species of plants have been identified By total mass, plants are the dominant organisms on Earth Common features include: –multicellular –eukaryotic –cell walls made of cellulose Most are autotrophic (photosynthetic); a few are parasitic

Plant Groups

Classifying Plants (video clip 5:26)video clip Nonvascular – no system of tubes to transport nutrients, water –Examples = mosses (bryophytes) Vascular – have tubes inside for transport

Types of Vascular Plants Seedless – have spores; eg. Ferns Gymnosperms – “naked seed;” cone-bearing

Vascular Plants (cont’d) Angiosperms – “enclosed seed;” fruit-bearing –Monocots – one seed leaf; flower parts in sets of 3; parallel veins on leaves –Dicots – two seed leaves; flower parts in sets of 2, 4, or 5; netted / branching veins on leaves

Plant Tissues

Three Types of Plant Tissues 1.Dermal tissue – protective outer layer; also functions in gas exchange and absorbing minerals –epidermis in nonwoody plants; coated with a waxy cuticle to reduce water loss –cork in woody plants; contains a waterproof chemical (no cuticle)

Plant Tissues, cont’d 2. Ground tissue – makes up inside of most plants, esp. nonwoody plants; provides structure and support; other functions depend on location in plant –in leaf – photosynthesis –in stem and root – storage of water, sugar, starch

Plant Tissues, cont’d 3. Vascular tissue – transports substances through plant –Xylem – conduct water and minerals from roots, through stems, to leaves –Phloem – conduct sugar and nutrients from leaves throughout body

Roots (video clip – 1:43)video clip absorb water & minerals –must get oxygen from soil b/c roots don’t photosynthesize – this is why overwatered plants can “drown” and die consist of: –vascular tissue (xylem, phloem) –cortex (surrounding ground tissue) –dermal tissue (root hairs, root cap)

Types of Roots taproot – large, central root; eg. carrot fibrous roots – highly branched, w/ many roots all the same size adventitious roots – grow from aboveground stems or leaves to extract water or oxygen from air; eg. orchids

Stems (video clip 3:16)video clip support leaves contain vascular tissue other specialized functions include: –water storage; eg. cactus –sugar / starch storage; eg. onion, white potato

Nonwoody/Herbaceous Stems xylem and phloem arranged in vascular bundles, surrounded by ground tissue –monocots – x & p scattered throughout –dicots – x & p arranged in ring; ground tissue outside ring = cortex, inside ring = pith

Woody Stems innermost cylinder (wood) is xylem; exterior to this is a cylinder of phloem covered by cork (phloem + cork = bark) –heartwood – nonfunctioning xylem in center of mature woody stems –sapwood – functioning xylem around heartwood

Leaf – Major Structures (video clip 2:52)video clip blade – flat part of leaf petiole – stalk connecting blade to stem cuticle – waxy coating veins – contain x & p

Leaf – Major Structures, cont’d mesophyll – ground tissue in leaves; full of chloroplasts; 2 layers –palisade layer – upper layer of close, columnar cells –spongy layer – bottom layer or loose, spherical cells stomata – in epidermis; opening surrounded by two guard cells; connects air spaces in spongy layer to outside air

Adapted/Modified Leaves large, broad – for moist, shady environments; eg. philodendron needles – for cold, windy environments; eg. pine w/ fleshy petioles - for food and water storage; eg. celery spines – for protection; eg. cactus tendrils – for climbing; eg. peas

Plant Reproduction May be asexual –Pro: faster than sexual reprodn –Con: offspring genetically identical to parent May be sexual –specifics of process vary between major plant groups

Plant Life Cycle Terminology sporophyte – 2n phase; produces spores in sporangium via meiosis spore – n reproductive cell; develops into gametophyte gametophyte – n phase; produces haploid gametes via mitosis; eggs produced in archegonium, sperm produced in antheridium gamete – n cells that fuse (fertilization) and give rise to 2n zygote (which develops into sporophyte)

Reproduction in Nonvascular Plants gametophytes are dominant sporophytes grow from, and remain attached to, gametophytes a film of water is needed for sperm to swim to nearby archegonia to fertilize eggs animation

Reproduction in Seedless Vascular Plants sporophytes are dominant sporophytes grow from, and then destroy, gametophyte animation

Reproduction in Seed Plants sporophyte dominant gametophytes only visible under microscope male gametophyte = pollen grains, which fertilize the female gametophyte in the ovule zygote then develops into embryo embryo and surrounding tissues becomes the seed animation