Buscar
Estás en modo de exploración. debe iniciar sesión para usar MEMORY

   Inicia sesión para empezar

level: 7.7 Transport of water in the xylem

Questions and Answers List

level questions: 7.7 Transport of water in the xylem

QuestionAnswer
What is xylem tissue- Transports water + mineral ions - Moves up plant from roots to leaves - Xylem + phloem are mass transport systems - move substances over large distances - No energy needed
Structure of the xylem- Xylem vessels, long, tube-like - Made of dead cells joined end-to-end - No end walls on cells, making an uninterrupted tube - So allows water to pass easily through middle
The cohesion-tension theory of water- Cohesion + tension help water move up plants against the force of gravity
How does cohesion-tension help water move up plants- Water evaporates from leaves at top of xylem - transpiration - This creates tension (suction), pulls more water into leaf, water is cohesive - Water moves from roots, to stem, upwards
Transpiration meaning- The evaporation of water from a plants surface, especially leaves
Process of transpiration- Water evaporates from moist cell walls - Accumulates in spaces between cells - When stomata open, it moves out of leaf down concentration gradient (there's more water inside leaf than the air outside)
The main factors that affect transpiration rate- Light - Temperature - Humidity - Wind
Light- Increase light increases transpiration rate (+ correlation) - Stomata open when it gets light to let CO2 in for photosynthesis - When its dark stomata close, little transpiration
Temperature- Increasing temperature increases transpiration (+ correlation) - Warmer molecules have more energy, evaporate from cells faster - This increases concentration gradient between inside + outside of leaf, evaporate from leaf faster
Humidity- Increasing humidity decreases transpiration (- correlation) - Dry air = concentration gradient between inside + outside of leaf decreases, decreasing evaporation
Wind- Increasing wind increases transpiration (+ correlation) - Blows away water molecules from around stomata - Increasing concentration gradient between the inside + outside of leaf, increasing evaporation
Potometer (pu - tom - eee - ter)- Used to estimate transpiration rates - Measures uptake by a plant, based on how far an air-water meniscus moves over time - But based on assumption that water uptake is directly related to water loss
Using a potometer- Construct potometer underwater, so no air enters - Cut shoot at slant, increases SA for uptake - Insert shoot underwater - Remove apparatus from water - Dry the leaves, allows time to acclimatise - Remove end of capillary tube until 1 air bubble has formed - Put end of tube back into water - Record the starting position of the air bubble - Start timer, record distance moved by air bubble per unit time e.g. per hour - Rate of air movement = estimate of transpiration rate - Change 1 variable, everything else kept constant
Dissecting plants- Look at phloem and xylem under microscope - Draw them
Dissecting plants method- Use a scalpel to cut cross-section of the stem - Cut sections thinly, better under microscope - Use tweezers to place sections in water, stops drying out - Transfer each section to dish containing stain e.g toluidine blue (TBO) - Leave 1 min - Rinse off sections in water - Mount each one onto slide
Toluidine blue (TBO) (tu - lu - i - deene)- Stains lignin in the walls of the xylem vessels blue-green