topic 9.1- transport in the xylem of plants Flashcards
what is transpiration an inevitable consequence of and why?
gas exchange in the leaf; if the stomata allow co2 to be absorbed, they must let water vapour escape
define transpiration
the loss of water vapour from the leaves and stems of plants
give the function of guard cells
- to minimise water loss
- guard cells control the aperture of the stoma
describe xylem vessels
- long continuous tubes
- walls thickened and impregnated with lignin (polymer)
- formed from files of non-living cells, arranged end-to-end
how does lignin help the xylem
lignin strengthens the xylem walls, so that they can withstand very low pressures without collapsing
the pressure inside xylem vessels is usually much ——- than atmospheric pressure but…
lower; the rigid structure prevents the vessels from collapsing
where would the xylem be in a vascular bundle
on the inside, next to the pith
why are the cohesive and adhesive properties of water important in transpiration?
- O atom in one molecule attracts H atom in other (due to polarity)= cohesion
- H2O attracted to hydrophilic part of cell walls of the xylem=adhesion
-> water can be pulled up from the xylem in a continuous stream
what maintains the transpiration stream?
tension in leaf cell walls
what generates tension forces in leaf cell walls?
the adhesive property of water and evaporation
describe how tension acts in transpiration
water evaporates:
- adhesion causes water to be drawn through the cell wall from the xylem
- this reduces xylem pressure, which generates a pulling force
adaptations of xerophytes (6)
- reduced/rolled leaves
- thicker wait cuticle
- stomata in pits with hairs (traps water vapour, making surroundings more humid)
- utilise CAM physiology
- lower growth to ground so less exposed to environmental conditions
- shallow roots
Really tired tudents may use loads of energy sources
CAM physiology
- stomata only open at night
- CO2 taken in at night is stored as magic acid, and this is done via the C4 pathway
what are halophytes
plants that live in saline soils
adaptations of halophytes (7)
- leaves reduced to small scaly structures/spines
- leaves shed when water scarce (stem can photosynthesise)
- water storage structures develop in leaves
- thick cuticle + multiple layer epidermis
- sunken stomata
- long roots
- structures for removing salt buildup
Little little water tickles spraying little sickles
