2 Transport in plants H2O & minerals Sugars Gas exchange transport in xylemtranspirationWater potential, adhesion & cohesionSugarstransport in phloembulk flowPhotosynthesis in leaves loads sucrose into phloemGas exchangephotosynthesisCO2 in; O2 outstomatarespirationO2 in; CO2 outroots exchange gases within air spaces in soil
3 Overview Sugars travel from leaves to roots through phloemWater and dissolved minerals travel from root to shootthrough xylemIt defiesgravity!
4 1. Transport of Water and Minerals Amount of water needed daily by plants is small compared to the amount that is lost through transpirationTranspiration:evaporation of water from plant surfaceIf water is not replaced, the plant will wilt and may die.
5 Hydrostatic pressure causes water to travel up tube Water PotentialWater movement is governed by differences in water potentialThe potential energy of water moleculesSolute concentration and pressureWater moves from an area of higher water potential to lower water potentialHigh solute concentration = low water potentialLow solute concentration – high water potentialPEHigh Water PotentialLow Water PotentialHydrostatic pressure causes water to travel up tubePE
6 The Process - Roots Minerals from the soil Actively transported into the root hairs and start to accumulateIncrease solute concentration in root cells, decrease water potentialWater moves in through osmosis to xylem cellsHigh Water PotentialWATERLow Water Potentialroot hairH2O
7 Hydrostatic pressure causes water to travel up xylem As water enters the xylem, it forces fluid up the xylem due to hydrostatic root pressurepositive pressureThis pressure can only move fluid a short distance.The most significant force moving the water and dissolved minerals in the xylemThe “pull” of water from transpirationcohesion & adhesionHydrostatic pressure causes water to travel up xylemPull =NegativePressure
8 Adhesion and Cohesion Water is a polar molecule unequal sharing of electrons in the covalent bondsoxygen atom has a stronger attraction for electrons then hydrogenO becomes slightly negatively chargedH becomes slightly positively chargedd–OHHd+d+H2O
9 Cohesion and AdhesionWater molecules are attracted to one another and other materialsCohesionDue to: Hydrogen BondsForce of attraction between slightly “–” oxygen and slightly “+” hydrogen of adjacent water moleculesAdhesionAttraction between water molecules and the side of xylem cells
10 Transpirational Pull Starts in Leaves Evaporation of water through stomataLowers WP in the surrounding air spacesWater moves from spongy cells (higher WP) to air spaces (lower WP)Water in spongy cells exerts a pull on column of water molecules in the xylem all the way from the leaves to the roots (adhesion, cohesion)
12 Mycorrhizae increase absorption Symbiotic relationship between fungi & plantsymbiotic fungi greatly increases surface area for absorption of water & mineralsincreases volume of soil reached by plantincreases transport of minerals to host plant
13 MycorrhizaeThe hyphae of mycorrhizal fungi extend into soil, where their large surface area and efficient absorption enable them to obtain mineral nutrients, even if these are in short supply or are relatively immobile. Mycorrhizal fungi seem to be particularly important for absorption of phosphorus, a poorly mobile element, and a proportion of the phosphate that they absorb has been shown to be passed to the plant.
14 2. Transport of Sugars Photosynthesis: CO2 + H2O C6H12O6 + O2 Storage form of sugar: StarchCannot be transported, must be broken down into smaller componentsTransport form of sugar: SucroseVery sweet sapUsable form of sugar: Glucose
15 Push and PullWater and minerals are mainly transported via transpirationnegative pressure or “pull”Sucrose is mainly transported via:positive pressure (hydrostatic pressure)“push” force (+) pressure due to accumulation of water“pull” force (-) pressure due to adhesion & cohesion
16 Companion cells ATP Cells that surround phloem Contain a lot of mitochondriaWhy?A lot of active transport!ATP
17 Transport of Sugars ATP Mass flow hypothesis Phloem loading in leaf “source to sink” flowSource = leaf, Sink = rootPhloem loading in leafactive transport of sucrose into phloemincreased sucrose concentration decreases water potentialWater flows in from xylem cellsincrease in pressure due to increase in water causes flowHydrostatic pressureATPcan flow 1m/hrIn contrast to the unidirectional transport of xylem sap from roots to leaves, the direction that phloem sap travels is variable. However, sieve tubes always carry sugars from a sugar source to a sugar sink. A sugar source is a plant organ that is a net producer of sugar, by photosynthesis or by breakdown of starch. Mature leaves are the primary sugar sources. A sugar sink is an organ that is a net consumer or storer of sugar. Growing roots, buds, stems, and fruits are sugar sinks. A storage organ, such as a tuber or a bulb, may be a source or a sink, depending on the season. When stockpiling carbohydrates in the summer, it is a sugar sink. After breaking dormancy in the spring, it is a source as its starch is broken down to sugar, which is carried to the growing tips of the plant.A sugar sink usually receives sugar from the nearest sources. Upper leaves on a branch may send sugar to the growing shoot tip, whereas lower leaves export sugar to roots. A growing fruit may monopolize sugar sources around it. For each sieve tube, the direction of transport depends on the locations of the source and sink connected by that tube. Therefore, neighboring tubes may carry sap in opposite directions. Direction of flow may also vary by season or developmental stage of the plant.
18 ATP Phloem unloading into root cells active transport of sucrose into root cellsDecreases pressure in bottom of plantSucrose will travel from high pressure near leaves to low pressure near rootsATP
19 3. Gas ExchangeWhat environmental conditions might impact transpiration of water?
20 Gas Exchange Regulation Epidermal cellGuard cellChloroplastsNucleusIn dry conditionswater leaves guard cells by osmosisguard cells become flaccidstomata close to prevent water lossIn humid conditionswater enters guard cells by osmosisguard cells become turgidstomata open to facilitate water flowH2OH2OH2OH2OH2OH2OH2OH2OThickened innercell wall (rigid)H2OH2OH2OH2OStoma openStoma closedwater moves into guard cellswater moves out of guard cells
21 Control of transpiration Balancing stomate functionalways a compromise between photosynthesis & transpirationleaf may transpire more than its weight in water in a day…this loss must be balanced with plant’s need for CO2 for photosynthesis
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