transport in plants Flashcards
what is meant by dicotyledonous plants
seeds contain 2 organs which act as for stores
transport vessels known as vascular system
transport tissues arranged in vascular bundle
describe the structure and function of xylem
non living tissue
transport water + mineral ions
provides support
xylem vessels
-long hollow structures made of several columns of cells fusing end to end
xylem parenchyma
- thick walls
- packed around xylem vessels
- store food
xylem fibres
- provides strength
- doesnt transport water
- long cells with lignified secondary walls
describe the structure and function of the phloem
living tissue
transport organic solutes from leaves
sieve tube elements
- main transporting vessel
- many cels joined end to end to form long hollow structure
- in-between cell walls become perforated to form sieve plates which let contents through
companion cells
-linked to sieve tube elements by plasmodesmata (microscopic channels through cellulose walls which link cytoplasms)
describe movement of water into the xylem
water moves across root until it reaches endodermis- layer of cells surrounding vascular tissue
water in apoplast pathway forced into cytoplasm- joining symplast pathway
solute conc in cytoplasm of endodermal cells lower than in xylem so water moves into xylem by osmosis
once in vascular bundle, water returns to app-last pathway
name adaptations of xerophytes
thick waxy cuticle
sunken stomata- reduce air movement
reduced N of open stomata- reduce water loss
reduced leaf SA
curled leaves- create still humid microenvironment
root adaptations
name adaptations of hydrophytes
air sacs- enable leaves to float small roots wide flat leaves- catch sunlight many always open stomata thin waxy cuticle
explain the apoplast route of phloem loading
sucrose from source travels through cell walls to companion cells + sieve tube elements
sucrose moved into cytoplasm= active process
hydrogen ions actively pumped out of cell into surrounding tissue and return down conc grad through co-transport proteins
water moves in as a result of high sucrose solution- builds turgor pressure
explain phloem unloading
sucrose unloaded from phloem into cells that need it through diffusion
diffuses rapidly to maintain conc grad
loss of solutes increases water potential in phloem so water moves out by osmosis
how is transpiration controlled
leaves waxy cuticle prevents rapid water loss
CO2 moves in and O2 moves out of stomata- which can be closed by guard cells
water vapour also leaves through stomata
how does a transpiration stream occur
as water evaporates from mesophyll cells, water potential is lowered so water over in from adjacent cell via osmosis
what is capillary action
water mols form hydrogen bonds with carbs of narrow xylem vessels (adhesion)
mols form hydrogen bonds with each other (cohesion)
adhesion + cohesion result in capillary action- water moves up narrow tube against gravity
what transpiration pull
water drawn up xylem to replace water lost by evapouration
what is the name given to products transported in translocation
assimilates
give examples of sources and sinks sources
sources-green leaves + stems
-storage organs
sinks
- growing roots
- dividing meristems
name factors that affect the rate of transpiration
+ correlation
soil water availability
temperature (more kinetic energy so water mols move faster)
light (more stomata open for PS)
- correlation
humidity (reduces water vapour potential)
