Plants. Plant Diversity About 280,000 species of plants have been identified By total mass, plants...
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Transcript of Plants. Plant Diversity About 280,000 species of plants have been identified By total mass, plants...
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