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level: 9.1 Xylem Transport

Questions and Answers List

level questions: 9.1 Xylem Transport

QuestionAnswer
What are the 2 types of active transport in root uptake?direct: protein pumps move ions against a gradient indirect: proton pumps expel H+ ions into the soil displaces the cations which diffuse back into the root
What are the organic molecules that plants make?glucose and starch
How are mineral ions up taken in the roots?actively transported = causes absorption of water by osmosis
What are the layers in the leaf called? and what are the functions of each layer? (3)upper palisade mesophyll = tightly packed w many chloroplasts (light absorption) lower spongy mesophyll = loosely packed with air spaces near stomata = increase gas flow vascular bundles between layers (xylem and phloem)
What are the 2 types of root systems?fibrous roots = thin and very spread out (increases SA for absorption) tap roots = penetrating w lateral branches (deeper reservoirs of water)
how is water uptake controlled by the casparian strip in roots? (4)absorbed by ROOT EPIDERMIS diffuses across CORTEX towards CENTRAL STELE pumped across CASPARIAN STRIP that is impermeable = controls uptake rate
What are vascular bundles? what are they used for?xylem and phloem is used for transporting materials
What does xylem transport?water = transpiration
what does phloem transport?nutrients (source to sink) = active translocation
What is transpiration?loss of water vapor from stems and leaves due to gas exchange
What are the steps of transpiration? (5)light energy converts water in the leaves into vapor water vapor is lost through evaporation new water is absorbed from the soil through the roots = P difference in leaves and roots water flows up stem (xylem) in mass flow along the pressure gradient
How does evaporation cause transpiration? (3)some light that is absorbed becomes heat = water becomes vapor in spongy mesophyll vapor diffuses out of stomata and is evaporated = tension forces negative hydrostatic P = draws new water out of xylem
How is water taken up into the root?it is taken up through osmosis when mineral ions are actively transported into the roots
What is mass flow?movement of fluid down a pressure gradient (roots - leaves) leaves = lower pressure bec of evaporation roots = higher pressure bec of osmotic uptake
What is capillary action?water rising through tubes against gravity due to cohesive and adhesive forces
What is cohesion? (4)water molecules stick together (hydrogen bonding) bw 2 particles of the same substance water is polar and can form H bonds through intermolecular bonding = water molecules can be pulled up the xylem in a continuous stream
What is adhesion? (6)when water molecules stick to the xylem wall (polar associations) bw 2 particles of different substances xylem wall + water are both polar = as water moves up by capillary action, pulls inward on the xylem to create more tension
What are the features of the xylem? (7)inner lining of dead cells fused into a continuous tube vessel element / tracheid hollow to enable water movement cell walls have thickened cellulose reinforced w/lignin = provides structural stability outer layer is perforated (pores) to facilitate water movement indents and pits
Why is the movement of water a passive process?bec the cells are dead and happen in one direction only
Which part of the plant regulates the transpiration rate?stomatal pores on the leaf's underside
How do stomata close?when the guard cells beside it loses turgor and becomes flaccid = by cellular signals in response to external triggers
How can transpiration be modelled? (3)capillary tubing filter paper porous pots
How does capillary tubing model transpiration? (4)water can flow in narrow spaces against gravity = capillary action bec of cohesive forces and adhesion to the walls thinner tube . less dense fluid = higher the liquid will rise
How does filter paper model transpiration? (3)absorbs water bec of cohesive and adhesive properties = similar to how water moves up the xylem paper and xylem wall are both made of cellulose
How does porous pots model transpiration? (3)semi permeable containers water loss is similar to evaporation of water in the leaves if an airtight seal is used = negative P = More liquid
What are potometers used for?used to measure the transpiration rate by measuring the distance travelled by an air bubble every minute
Why is not all the water lost to transpiration?a small amount is used in photosynthesis and to maintain the turgidity of the plant
What factors increase transpiration rate? (3)light = opens stomata for photosynthesis = more water vapor lost temp = increases evaporation = more water loss in leaves wind = more air flow removes water vapor = more diffusion
How can all the factors affecting transpiration rate be tested with a potometer? (4)light = diff distances from a lamp temp = heaters / heated water baths wind = fans to circulate air around the plant humidity = plastic bags with diff levels of vapor
What are xerophytes?desert plants they have higher rates of water loss bec of high temps increasing evaporation rate
How are xerophytes adapted to conserve water? (4)thick waxy cuticles = prevents water loss from leaf surface low growth and small leaves = small SA rolled leaves with stomata in pits = traps WV CAM physiology = stomata closed during the day
What are halophytes?saltmarsh plants that have low levels of water uptake bec of high salinity in the soil reducing osmosis rates
How are halophytes adapted to conserve water? (4)cellular sequestration = separating ions and salts in vacuoles tissue partitioning= concentrating salts into specific tissues root level exclusion = root structured to exclude salt salt excretion = glands to eliminate salt
When is the hormone ABA released in plants? (6)when a plant begins to wilt from water stress the dehydrated mesophyll cells release ABA = causes K to flow out from guard cells = reduces water P = loses turgor = stomata closes bec the guard cells become flaccid = blocks opening
What are tracheids?tapered cells that exchange water through pits = slower water transfer rate
What are vessel elements?end walls are fused to form a continuous tube = faster water transfer
How are minerals taken up in plants?1) fertile soil has negatively charged clay particles for cations to attach to 2) passively diffuses into the roots 3) indirect active transport = H+ ions are released by proton pumps in the roots 4) these ions displace the positive ions from the clay = diffuse into the root along a gradient 5) anions can bind to the H+ ions and be reabsorbed with the proton
How is water taken up from the roots?follows the mineral ions with mass flow through osmosis to a region of higher solute concentration
What is the symplastic and apoplastic pathways?the way water moves towards the xylem symplastic = cytoplasm apoplastic = through cell wal
How is the cytoplasm of the cells connected for water to pass through?plasmodesmata
At what point can the water not cross in the apoplastic pathway?when it reaches the casparian strip = transferred to the cytoplasm