Water Transport in Plants As Flashcards
what are xylem
hollow tubes that transport water. dead hollow cells that form continuous column
define transpiration
water evaporates out of stomata on leaves of plant
transpiration helps to transport materials in plants
what does cohesion tension theory explain
the tension caused by water loss from the top (stomata) and water moving in at the bottom (root pressure)
what is transpiration increased by
light intensity
temperature
air molecules
air humidity
process of transpiration
lower water potential in mesophyll water pulled up xylem water molecules cohere/stick together by hydrogen bonds forming a continuous water column adhesion of water to walls of xylem
what equipment is used to measure water uptake
potometer
how to step up a potometer
must be airtight cut shoot at slant and place underwater insert apparatus no air bubbles at start note where bubble is to start measure distance moved by bubble
how to calculate the rate of transpiration with photometer
Πr^2 x distance air bubble moved
why does light intensity affect rate of transpiration
the stomata open to allow CO2 in for photosynthesis
how does temperature affect rate of transpiration
the kinetic energy of water molecules increases. molecules move faster
how does air movement affect rate of transpiration
removing the moist air surrounding the leaf lowering the water potential
how does air humidity affect rate of transpiration
affects the water potential gradient
how to find rate loss per mm2 of surface area of leaves
draw around leaves on graph paper and count square/repeat on both sides of leaf/ divide rate by total surface area
why is potometer rate not really transpiration rate
water lost in respiration
used in photosynthesis
leaks in apparatus
define xerophyte
plant which needs very little water
how do xerophytes reduce water loss
thick cuticle
rolled up leaves (traps air becomes moist and reduces water potential gradient)
hairy leaves (for same reason)
smaller surface area/volume ratio of leaves (slower diffusion)
water potential gradient is reduced by keeping water vapour close to the outside of the stomata
define phloem
tissue that transports biological molecules in either direction
what are phloem made of
made of sieve elements arranged end to end. walls perforated by sieve plates. companion cells associated with sieve tube elements
what is evidence for cohesion-tension theory
tree trunks have a wider diameter at night when transpiration is at lowest point (less tension)
what happens if xylem is broken
water doesn’t leak out and air enters so water can no longer enter plant
define sources
where sugars are made during photosynthesis
define sinks
where sugars are used or stored
what is the mass flow hypothesis
sugars in source actively transported into phloem by companion cells
lower water potential of sieve cell/tube
water enters by osmosis
increase in pressure causes mass movement (towards sink/root)
sugars used/converted in root for respiration for storage
what is evidence of translocation in the phloem
ringer and tracer experiments
phloem sap feeders are used to show phloem transports sugars. they feed without jaw muscles because there is a high hydrostatic pressure in phloem
