Translocation

Question 1

What is translocation?

Answer 1

The movement of dissolved substances (assimilates) to where they are needed in a plant.

• This process requires energy.

Question 2

What is a “source” ?

Answer 2

A source is where the substance is made ( this is where that substance has a HIGH concentration)

Question 3

What is a “sink” ?

Answer 3

A sink is the area where the substance is used ( this is where it is in LOW concentration)

Translocation moves substances from sources to sinks.

Question 4

What sugar is transported as and why?

Answer 4

Sucrose:

• As it is metabolically inactive and soluble, so it doesn’t get used up during transport

Question 5

How is a concentration gradient maintained from a source to a sink?

Answer 5

By using enzymes
which change the dissolved substances at the sink or even breaking them down.

• This makes sure there is always a lower concentration at the sink, maintaining the concertation gradient

Question 6

What dies the enzyme “invertase” do ?

Answer 6

Breaks down sucrose into glucose, to be used by the plant

• This also helps maintain a step concentration gradient , as this make sure there is a low concertation of sucrose at the sink.

Question 7

1) Mass flow ( source end)

Answer 7

• Active transport actively loads solutes into sieve tubes,
• reducing the water potential inside the tubes, so water from xylem and companion cells move into the tubes by osmosis
• This creates a high pressure inside the sieve tubes at the source end of the phloem.

Question 8

2) Mass flow (sink end)

Answer 8

• At the sink end solutes are removed, increasing the water potential inside the sieve tubes,
• so water leaves the tubes by osmosis
• This lowers the pressure inside the sieve tubes at the sink end.

Question 9

3) Mass flow ( pressure gradient)

Answer 9

• This results in a pressure gradient from the source end to the sink end.
• This pressure gradient pushes solutes along the sieve tubes to where they are needed

Question 10

Active loading process:

Answer 10

ATP is used to actively transport H+ ions to move in and out of the companion cell.

• This creates a concentration gradient as there is more H+ ions outside of the membrane compared to inside
• H+ ions bind to a co-transporter protein in the companion cell membrane and re-enters the cell DOWN the concertation gradient
• A sucrose molecule binds to the co- transporter protein at the same time, and the movement of the H+ ion is used to move the sucrose into the companion cell AGAINST its concentration gradient

sucrose molecules are then transported out of companion cells and into sieve tubes .