Phloem and Translocation

Question 1

What is the phloem?

Answer 1

Plant vessels that transport sugars.

Question 2

What are sieve tube elements?

Answer 2

• cells that make up phloem vessel
• living cells - contain cytoplasm but no nucleus
• walls made of cellulose

Question 3

What are companion cells?

Answer 3

• connected to sieve tube elements via plasmodesmata
  -> allows cytoplasm to be shared between these + sieve tube
• have a nucleus

Question 4

What are sieve plates?

Answer 4

• at either end of sieve tube elements
• have large pores -> allows sap to move
• allows sugars to be transported

Question 5

What is translocation?

Answer 5

Proceeds where sugars produced in photosynthesis are transported from plant leaves to other parts

Question 6

What are the steps of translocation? (Summary)

Answer 6

1. Active transport of sucrose
2. Diffusion of Sucrose
3. Osmosis 1.
4. Unloading of Sucrose
5. Osmosis 2.

Question 7

What are the steps of Translocation (detailed)?

Answer 7

1. Sucrose produced at source AT into companion cells (energy provided by mitochondria in CC.)
   —> H+ AT out of CC and then diffuses back into CC with sucrose (Cotransport.)
2. Loading of sucrose into phloem causes concentration of sucrose to increase.
   —> sucrose diffuses from CC into sieve tube elements.
3. Inc sucrose conc in phloem