Chapter 9.4

Question 1

What is translocation?

Answer 1

Translocation is the transport of assimilates (sugars and chemicals made by plant cells) throughout the plant

Question 2

In what form are plant sugars transported in?

Answer 2

Sucrose

Question 3

Where does translocation occur?

Answer 3

• Translocation occurs in the phloem tissue

- Sucrose is released into the phloem at sources and taken out of the phloem at sinks

Question 4

How does sucrose enter the phloem?

Answer 4

1. Loaded in by active process
2. Companion cells use ATP to transport hydrogen out of cells into cytoplasm
3. This establishes a diffusion gradient
4. Hydrogen ions diffuse back in through special cotransporter proteins
5. These allow hydrogen to bring sucrose molecule back in with them
6. Sucrose molecules build up in the companion cell
7. Diffuse into sieve tube elements through plasmodesmata

Question 5

How is sucrose moved through the source?

Answer 5

1. Sucrose enters sieve tube element
2. Reduces water potential
3. Water molecules move in by osmosis
4. Increase hydrostatic pressure at the source

Question 6

How is sucrose moved along the phloem?

Answer 6

1. Water enters at source
2. Moves down hydrostatic pressure gradient towards sink
3. Produces water flow
4. This carries sucrose and other assimilates along the phloem
5. This is called mass flow
6. Can occur both up and down a plant

Question 7

How can sucrose be used?

Answer 7

• Can be converted into starch for storage

- Can be used in metabolic reactions

Question 8

How is sucrose moved through the sink?

Answer 8

1. Sucrose used in cells surrounding phloem
2. This reduces sucrose concentration
3. Sucrose molecules move out of the sieve tube elements
4. Water potential in sieve tube elements increases, so water moves out by osmosis
5. This reduces hydrostatic pressure at the sink