2 - mass transport in plants Flashcards
Factors affecting rate of transpiration
Light (positive correlation)
Temperature (positive correlation)
Humidity (negative correlation)
air flow (positive correlation)
Transpiration
The loss of water vapour through evaporation from a plant’s surface.
Cohesion - Tension Theory
Cohesion
-Water molecules attracted to each other because of hydrogen bonds, creating a column of water
Adhesion
-attraction of water to non-water molecules, such as molecules that make up xylem wall
-narrower xylem, greater adhesion effect so easier to transport water
Root Pressure
-As water moves into roots, pressure inside roots increases and forces water above it upwards
Phloem
transports dissolved substances, such as sucrose and amino acids from parts of the plant where they are made (sources) to the parts of the plant where they are used (sinks)
Made up of two types of cells:
1) Sieve Tube
-Living
-No nucleus and few organelles so more space for solutes to be transported
2) Companion cells
-Provide ATP
apoplast pathway
moves water through cell walls, dead cells, and xylem
diffusion
quick
more common
when water reaches Casparian strip, must take the symplast pathway
symplast pathway
moves water through cytoplasm, plasmodesmata, vacuole of the cells
osmosis
slower
plant viruses
responsible for losses in crop production and quality of produce
range of symptoms:
yellowing of leaves,
leaf distortion
abnormalities
aphids
have sucking mouthparts called stylets
feed by inserting the stylets into phloem vessels and the sap, which is under high pressure, is forced into the aphid’s gut
Some species produce winged females which migrate to start colonies on a new host plant
mass flow hypothesis
Sucrose at source actively transported to phloem cells
Lowers water potential of sieve cell
Increase in hydrostatic pressure near source causes mass movement towards sink
In sink, sugar removed from phloem
