Chapter 25- Plants.docx

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University of Toronto Scarborough
Biological Sciences
Rene Harrison

Biology: Chapter 25 Characteristics of Land Plants -eukaryotes -most are photoautotrophs -alternation of generation: different life cycle than animals -meiosis gives rise to spores: plants’ gametes; asexual reproduction -green algae: -haploid stage dominates the life cycle -single-celled zygote is the only diploid stage-> haploid spores -land plants: -2 multicellular stages-> haploid + diploid -diploid-> sporophyte: spore producing plant -haploid-> gametophyte: gamete- producing plant; nourish + protect sporophyte’s next generation -begins in specialized cells of sporophyte -when the spore germinates, divides by mitosis-> gametophyte -embryo is retained inside gametophyte tissue Transition to Life on Land -cyanobacteria were the first to adapt to land; green algae + fungi followed after -green algae probably evolved into today’s plants-> charophytes -450 million years ago, probably -Kingdom Plantae-> 30000 species-> 10 phyla -earliest land plants lacked a cuticle: outer waxy layer preventing water loss -also lacked specialized tissues for water transplant -restricted the plants to remain in moist habitats -poikilohydric: little control over internal water content -> later evolves to have stomata to regulate water/ gas diffusion -other bacteria had colonized the land before plants began to -problems for plants to grow taller + upright -require strength to grow, against gravity -will need internal water circulation system, since diffusion wouldn’t be as effective ->xylem: specialized tissues; transports water through plant body -lignin: tough polymer; supports xylem; helps strengthen cell wall; allow upward growth -xylem is a kind of vascular plant: conducts sugars through the plant body -also phloem Eg) redwood grows very tall, plenty of lignin -apical meristem: constantly dividing shoots + roots producing tissue of plant body; in vascular plants -foundation of a plant’s branding + root system -nonvascular plants are not differentiated into roots + stems -roots: anchoring structures that absorb water + nutrients -came from vascular plants -rhizome: horizontal stem that penetrates the soil to anchor the plant -above ground, a shoot system evolved in vascular plants -stems + leaves that come from apical meristems -leaves represent modifications of stems -as plants evolved, their haploid gametophyte stage became less long and less complex -diploid sporophyte stage became longer in vascular + nonvascular plants -sporophyte stages: mitosis-> meiosis-> fertilization -sporangia: spore-producing chambers; produces spores by meiosis -transitition to becoming dominantly diploid due to advantage of being diploid on land -mutations in haploids (one DNA str
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