Translocation

Question 1

definition of translocation

Answer 1

movement of dissolved substances (eg sugars like sucrose, and amino acids), to where they’re required in the plant

Question 2

What are ‘assimilates’?

Answer 2

dissolved substances

Question 3

In which vessel does translocation occur in?
Does it require energy?

Answer 3

occurs in phloem and requires energy

Question 4

What is the term for the area that substances are moved from?

Answer 4

the ‘source’

Question 5

What happens in the ‘source’?
Give an example

Answer 5

-where a substance is made and is in high concentration
-eg. leaves are source for sucrose (photosynthesis)

Question 6

What is the term for the area that substances are moved to?

Answer 6

the ‘sink’

Question 7

What happens in the ‘sink’? Give an example of a sink

Answer 7

-where a substance is used up and is in low concentration
-eg other parts of plant such as food storage organs and meristems

Question 8

How is the concentration gradient ensured?

Answer 8

-enzymes change/break down dissolved substances at the sink to ensure there is always a lower sucrose concentration there
-always a concentration gradient between sink and source

Question 9

What enzyme breaks down sucrose in potatoes?

Answer 9

starch

Question 10

Which parts of a plant can act as both sinks and sources?

Answer 10

roots and leaves

Question 11

What is active loading?

Answer 11

process used to move substances from surrounding tissues, to companion cells, into sieve tubes, all against a concentration gradient

Question 12

What process and biological feature are used in active loading?

Answer 12

-active transport
-co transporter proteins

Question 13

Why are co transporter proteins and active transport needed?

Answer 13

there’s usually a higher sucrose concentration in companion cells, and even higher in sieve tube cells

Question 14

What is ATP and why is it necessary in active loading?

Answer 14

-one of the products of respiration
-breakdown of ATP supplies initial energy needed for active transport of H+ ions

Question 15

1st step in active loading

Answer 15

in the companion cell, ATP is used to actively transport H+ ions out of the cell and into surrounding tissue

Question 16

2nd step in active loading

Answer 16

this means there are more H+ ions in surrounding tissue than in companion cells, which creates concentration gradient

Question 17

3rd step in active loading

Answer 17

H+ ions re-enter cell, down a concentration gradient, once they’ve bound to a co-transport protein which in turn is bound to a sucrose molecule, in the companion cell membrane

Question 18

What is the result of H+ ions re-entering the cell, down a concentration gradient?

Answer 18

sucrose molecules are moved into the cell, against the concentration gradient

Question 19

4th step in active loading

Answer 19

sucrose molecules transported from companion cells, into sieve tubes by same process

Question 20

What is the mass flow hypothesis?

Answer 20

process of how translocation happens

Question 21

What happens in the source end of the phloem?

Answer 21

-solutes actively loaded into sieve tubes via active transport
-water potential is therefore lowered so water also moves into sieve tubes via osmosis, from xylem and companion cells

Question 22

What is the pressure and water potential like in the source end?

Answer 22

-high pressure created in sieve tubes
-low water potential

Question 23

What happens in the sink end of the phloem?

Answer 23

-solutes removed from phloem at sink end, to be used up
-water potential inside sieve tubes increases, so water leaves via osmosis

Question 24

What is the pressure and water potential like in the sink end?

Answer 24

-pressure is lowered inside sieve tubes
-high water potential

Question 25

What is the pressure gradient in the mass flow hypothesis, and why is it necessary?

Answer 25

-gradient from source end to sink end created
-gradient pushes solutes along sieve tubes to where they’re needed