3.1.3 transport in plants Flashcards
list the features of a dicotyledonous root
Xylem found at centre of root in a star shape
Phloem found outside in between each point of the xylem
epidermis
cortex
root hair with meristem and root cap
endodermis
casparian strip
pericycle
list the features of a dicotyledonous stem
Several vascular bundles - xylem found on inner edge of each bundle, phloem on outer edge of each bundle
epidermis
cortex
cambium in between xylem and phloem - meristematic tissue containing actively dividing pluripotent cells
pith
list the features of a dicotyledonous leaf
waxy cuticle
upper epidermis
palisade cell layer
spongy layer
vascular bundle down centre of leaf as a vein - xylem towards top of leaf, phloem towards bottom
lower epidermis
guard cells + stomata
what is transpiration
loss of water vapour from stems and leaves due to evaporation
XYLEM
what factors affect transpiration rate
light intensity - stomata open so larger SA for evaporation
relative humidity - more humid outside reduces water potential gradient
temperature - more heat, more kinetic energy
movement of air - more wind, blows away humid air so water potential gradient maintained
how do we measure transpiration rate
potometer - movement of air bubble along cylinder due to water evaporation
rate = volume/time
how do you measure the volume of a cylinder
πr² x length
what is a mass potometer
plastic wrap around bottom to prevent evaporation from soil and place pot on balance
mass decreases over time due to transpiration
explain the process of transpiration
- water evaporates from leaf cells, decreasing water potential
- water moves from xylem into leaf cells via osmosis
- as water moves into leaf cells it pulls water molecules in xylem behind it upwards - due to hydrogen bonds between molecules creating cohesive forces and adhesion to lignin in xylem walls (COHESION-TENSION THEORY)
- water moves into root hair cell by osmosis to replace water that’s moved up the xylem
- as water moves through plant it helps transport minerals dissolved in it towards leaves
how do mineral ions enter a plant
by active transport into the root hair cells which causes cell to have a lower water potential than soil
how does water move into a root hair cell
by osmosis because it goes from a high water potential in soil to low water potential in root hair cell (down water potential gradient)
what does symplastic mean
water moves through cytoplasm by osmosis down the water potential gradient from root hair cell to xylem
what does apoplastic mean
water moves through cell walls due to cohesive forces like capillary action
stops at endodermis as casparian strips act as a barrier
what is translocation
movement of sucrose from cells where sugars are made (source) to cells that need them (sink)
PHLOEM
what is the mass flow hypothesis
photosynthesis produces glucose (makes sucrose when added to fructose)
sucrose dissolves to phloem via symplast pathway and companion cells
sucrose levels increase so water potential decreases
water moves by osmosis from xylem
increases water levels which increases hydrostatic pressure so there’s a pressure gradient between source and sink
sucrose moves down gradient and diffuses into sink so water potential of phloem increases and water leaves phloem by osmosis
what is active loading for
sucrose transported by the apoplastic pathway
describe the process of active loading
active transport of H+ out of cytoplasm
high H+ concentration out of cell
H+ diffuses down concentration gradient - sucrose is cotransported
sucrose in cytoplasm
what are xerophytes
plants that have evolved to live in condition where water is very scarce
what are the adaptations of cacti
leaves replaced with spikes
photosynthesis occurs in stem
stomata in stem surface sunk into pits - only open t night
spines to trap moist air
thick waxy cuticle
long shallow roots or deep roots for storage
what are the adaptions of marram grass
leaves roll into tube with stomata inside traps moist air
thick waxy cuticle
long roots deep to find water or shallow to retain water in sand
Phloem tissue structure
Contains 2 key cells:
- sieve tube elements
- companion cells
Sieve tube elements
Living cells
No nucleus
Few organelles
Perforated end walls
Assists in mass transport of fluids
Companion cells
Provide ATP required for active transport of organic substances into sieve tube elements
Xylem tissue structure
Dead and hollow cells
No organelles or end walls, stack up on each other to make continuous hollow column
Xylem wall strengthened by lignin
