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)

• 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’d3. 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)

• 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)

• 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)

• 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