Transport In Plants Flashcards
Why are the root hair cells efficient surfaces for exchange of substances?
1) Large SA
2) Short diffusion pathway
What are some features of the apoplastic pathway?
1) Water is draw into the endodermal cells
2) Cohesive properties pull water along
3) The mesh structure of cellulose cell walls creates little resistance.
How does the symplastic pathway take place?
The water passes through the cell walls along the plasmodesmarta and through the cytoplasm
How does water travel into the xylem?
1) Water reaches the endodermis where the casperian prevents it progressing
2) Water is forced into the protoplast where it join water from the symplastic pathway
3) Active transport of salts into the xylem lowers the water potential
4) Water follows by osmosis which creates a force moving up the plant. (osmotic root pressure)
When will water move out of the stomata?
Humidity of the atmosphere is less than the air spaces next to the stomata
What are the 2 mechanisms that allow water to move up the stem?
1) Cohesion-tension theory
2) Root pressure
What 4 factors affect transpiration?
1) Light- stomata open during the day only
2) Temperature- transpiration occurs faster at high temps
3) Humidity
4) Air movement
How can xerophytes plants reduce water loss?
1) Sunken stomata
2) Rolling leaves
3) Reduce SA to volume ratio of leaves
4) Thick waxy cuticle
5) Hairy leaves
What are some features of sieve tubes?
1) They contain perforations in the cell walls
2) No nucleus and minimal organelles= more space for solutes
3) Cell walls are made of cellulose allowing for lateral and vertical movement.
What are the features of the companion cell?
1) Located next to each sieve tube
2) Contains nucleus and organelles
3) Controls the movement of solutes and provides ATP for active transport in the sieve tube
4) Plasmodesmarta connect the sieve cell and companion cells
What is translocation?
The active movement of organic substances around the plant
What is the mechanism of translocation?
1) Sucrose is loaded into the phloem at a source (leaves) - campanion cells lose H ions and create a concentration gradient
2) Protein carrier involved in the loading has one site for sucrose and one for H+ ions hence why a high conc of H+ is needed outside the cell
3) Sucrose diffuses down a concentration gradient into the sieve tube via the plasmodesmata
4) Sucrose will be unloaded elsewhere into the plant from the phloem into a sink
