Chapter 7: Transport in Plants

Question 1

transport of food by phloem (define the process)

Answer 1

translocation- moving of food (soluble organic substance) from one location to another

Question 2

what is liquid in phloem sieve tube called

Answer 2

phloem sap

Question 3

what is mass flow

Answer 3

• translocation of food to and from places is due to mass flow resulting from diff in pressure between location
• diff in pressure created by energy-ATP hence phloem transport is an active process
• mass flow movement is 1mh^-1

Question 4

explain translocation in terms of mass flow

Answer 4

At source:

• leaf mesophyll cell/chloroplast photosynthesises that makes triose sugar; some is converted to sucrose
• H+ pumped out of companion cell into cell wall using ATP as energy source. this creates large excess of H+ in apoplastic pathway outside companion cell-cell wall
• it can move back into cell down conc. gradient through carrier proteins for both H+ and sucrose at same time
• sucrose carried through cotransporter molecule into companion cell against conc. gradient
• sucrose can move from companion into sieve tube through plasmodesmata- symplastic
• high conc of sucrose inside sieve element decreases water potential in sap inside it hence water enters sieve element moving down a WP gradient by osmosis which creates high pressure

At sink:

• -unloading sucrose in tissues that need
• sucrose moves out of phloem into tissues using sym and apo plastic routes

Question 5

what are source and sink

Answer 5

source- area of plant in which sucrose is loaded into phloem
sink-area where sucrose it taken out of phloem