9.1 Xylem transport Flashcards
Define transpiration
TRANSPIRATION: loss of water vapour thrpugh the stems and leaves of a plant
Explain process of transpiration
Some light E converted into heat - water in spongy mesophyll into vapour - evaporate through stomata - new water is _absorbed by root_s from soil creating different pressure gradients in roots (high) and leaves (low) - water is pulled via xylem along the pressure gradient (in transpiration stream by transpiration pull)
Define stomata
STOMATA: pores on the underside of the leaf which facilitate gas exchange needed for photosynthesis
Leaf anatomy
Stem anatomy
Root anatomy
What influences rate of transpiration?
- opening of stomata (levels of photosynthesis - gas exchnage)
- humidity of the environment
- wind
- light intensity
How stomata regulate water loss?
Stomata open/close:
- dehydrated cells release plant hromone abscisic acid ABA - triggers efflux of K+ from guard cells - decrease water pressure (lose turgor) - stomata close
What makes transpiration stream possible?
Water adhesive (xylem polar - intermolecular associations - additional tension) and cohesive (H bonds - continuous stream) peroperties
Explain xylem
- from tracheids (exchange water via pits) and vessels (main traspiration stream)
- tubes composed of dead cells
- water movement passive
- many pores - pits - water transferred to cells
- walls thicker cellulose and lignin - strength as water creates tension
Way in which lignin may be deposited
Adaptation of roots
Roots - very branched off - root hairs - increase SA by which minerals, ions and water can be taken up
Tissues in roots
Explain mineral uptake by roots
Needed to take up: Mg2+, K+, Na+, NO3-, PO4-
Can be taken up by diffusion or active transport - root cells contain ion pumps that expel H+ - displace the cations in soil (indirect active transport) - diffusion along a gradient - anions may bind with H+ and reabsorbed
Explain water uptake by roots
Via osmosis to higher solute conc - by aquaporins - once inside the cell will move into xylem:
- symplastic route: via cytoplasm, water moves continuously between cells and plasmodesmata,
- apoplastic route: via cell wall, cannot pass Capsarian strip - run through cytoplasm of endodermis
Explain water conservation adaptations by two types of plants
Xerophytes: tolerate dry conditions: reduced SA, exposure of stomata for water loss, thickened cuticle, CAm open stomata at night
Halophytes: tolerate salty conditions: can isolate toxins, salts in vacuoles and cell walls, abscission, salt glands, flowering at humid seasons
Experiments modelling the movement of water up the xylem
- capillary tubing: traspiration pull/stream, adhesion + cohesion
- filter paper: movement up xylem, adhesion + cohesion - paper and xylem from cellulose
- porous pots: loss of water through pores similar to trasnpiartion
Explain potometer
POTOMETER: device that is used to estimate transpiration rates by measuring rate of water loss/uptake
Plant fixed to a potometer - water uptake assesed by movement of a air buble along a ruler - important to remember that not all water is lost due to transpiration - some used for metabolism
Controlled variables of experiment with potometer
- temperature
- humidity
- wind
- light intensity
