B8 - transport in plants (transpiration & translocation) Flashcards
function of xylem
-carry water & mineral salts from the roots to the leaves
-support the plant
function of phloem
carry sucrose & amino acids from the sources to the sinks
source: eg. leaves
sinks: eg. roots, flowers, fruit
5 things about xylem vessels
-transports water & dissolved minerals
-transported from root to leaves
-dead = no cytoplasm, nucleus, cell membrane
-lignin - strengthens cellulose cell walls - adds support
-no end cell walls = hollow tube
5 things about phloem sieve tube
-transports sucrose & amino acids
-transported from source to sink
-has a companion cell
-sieve plates have holes
-sieve tubes are living;; thin strands of cytoplasm, no nucleus & some organelles
locations of xylem vessel in:
root
stem
leaf
root - X shape
stem - inner
leaf - top
locations of phloem vessel in:
root
stem
leaf
root - outer of X
stem - outer
leaf - bottom
function of root hair cell
-minerals enter by active transport
-water enters by osmosis
adaptation of root hair cell
-larger surface area = faster absorption
-lots of mitochondria = more respiration = more E for active transport
pathway for water into the plant
-water enters root hair cell by osmosis
-root hair cell is hypertonic to surrounding soil water = low wp
-water moves through root cortex by osmosis
-water enters xylem vessel & rises by transpiration pull
-water moves in spongy mesophyll by osmosis
-water evaporates into spaces above stomata
-water leaves from stomata by diffusion
define transpiration
-loss of water vapor from plant leaves by evaporation of water at the surface of the mesophyll cells followed by diffusion of the water vapor through the stomata
-unidirectional
does water loss = transpiration?
-no, some water could be used for photosynthesis
but we assume for most part
explain the mechanism of water movement up the stem of a plant
-evaporation from leaves
-water molecules held tgt by cohesion
-pulls water molecules up the xylem
process of transpiration
-water vapor diffuses out of the stomata after it evaporated in the spongey mesophyll
-reduction of water potential at the top of the xylem causes a transpiration pull on the water molecules because they are held together by cohesion
-water enter the plant down a concentration gradient through osmosis in the root hair cell
factors of transpiration
-temperature
-humidity
-wind speed
-light intensity
how does temperature affect transpiration
-more transpiration
-more thermal E for evaporation, more kinetic E for diffusion
-only up till optimum temp
how does humidity affect transpiration
-less transpiration
-higher wp outside stomata, less steep concentration gradient, less diffusion
eg. monsoon
how does wind speed affect transpiration
-more transpiration
-pocket of humid air (water vapor) is blown away, more steep concentration gradient, more diffusion
how does light intensity affect transpiration
-increase transpiration
-darkness will cause stomata to close
how to change the factors of transpiration
temp - thermostatically controlled water bath/ distance from a heater
humidity - plastic bag over the plant’s leaf
wind speed - use a fan with varying speed
light intensity - use a lamp
cause of wilting
loss of water exceeds intake
wilting events
-plant loses water, mainly by transpiration
-vacuole shrinks
-cell becomes flaccid (low water pressure)
-plant is no longer supported; wilts
define translocation
-movement of sucrose & amino acids in phloem from sources to sinks
-bidirectional
define sink & eg
-part of plant the uses/ stores sucrose/ amino acids
eg. fruit, flower, nector
define source & eg
-part of plant the releases sucrose/ amino acids
eg. leaf, seed
note: before the experiment, let the plant adjust to the change for 10min
note: oil prevent water loss by evaporation
features of a bubble potometer
-bung
-reservoir of water
-tap
-air bubble
-capillary tube
units to measure rate of transpiration
mm/ min
independent, dependent & control variables for wind speed effect on transpiration
independent: fan speed (0, 1, 2, 3)
dependent: distance the bubbles travels in 10 min
control: temp (thermostatically controlled water bath), humidity, light intensity, plant species, same no. of leaves (use same plant), distance btw fan & plant
method for wind speed effect on transpiration
-set up the apparatus the diagram shows
-weight the whole apparatus at the start
-for each fan speed, leave it 10 min with 5 mins before the timer for equilibration
-weigh the apparatus again
-calculate the mass difference
-repeat for each fan speed 3 times & find the mean mass diff
conclusion for wind speed effect on transpiration
-more fan speed, more water loss; faster evaporation & steeper concentration gradient
3 ways to improve wind speed effect on transpiration experiment
-use a bubble potometer
-more repeats
-more fan speed
