BIOB 110CS 1st Edition Lecture 17 Xylem Water and nutrients move passively through the xylem Transpiration Cohesion Hypothesis how water gets to the top of a tree o Evaporation occurs in the cell walls cohesion holds water columns together in xylem lower water potential in root cells draws more water from the soil Xylem snap prevents cut flowers from lasting as long as they could It is an air bubble in the xylem To avoid this cut the lowers while the stems are underwater Plant vascular systems Sugar loading into phloem cells is the only process that requires energy Ongoing transpiration is necessary Growth patterns Animals have determinate growth predetermined organs and bilateral symmetry mostly Plants have indeterminate growth adjustable organ production and timing plasticity and spiral phyllotaxy Growth is due to cell elongation controlled by auxin and cell division in primary meristems Wood Before trees produced bark they could only grow to 30 feet tall Wood and bark are produced by a secondary meristem called vascular ambium Wood is layers of pectin and lignin laid between adjacent cellulose cell walls In mature trees 99 of the tissue is dead made of lignin These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Bark and cork are made of lignin suberin phenolics and wax and tannins phenolics Lenticels are exchanged between bark and other tissues for extra gas exchange Pendochronolgy is the use of tree growth rings for studying climate change fires and ecological trends Rafting ling up the vascular cambium Roots Anchor shoots absorb water and minerals store carbohydrates and associate with microorganisms The first sign of germination is when the radicle primary root extends Roots hairs absorb things in the soil and are constantly moving to explore the soil Different root systems allow for different species to occupy all of the soil
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