translocation

Question 1

What is translocation in plants? (2)

Answer 1

The movement of dissolved substances assimilates like sucrose

From a source where sugars are made to a sink where sugars are used or stored via the phloem

Question 2

What are the source and sink in plant translocation? (2)

Answer 2

Source Where sugars are produced e.g. leaves

Sink Where sugars are used or stored e.g. roots or growing leaves

Question 3

How are hydrogen ions involved in translocation? (2)

Answer 3

1 ATP is used to actively transport hydrogen ions out of companion cells

2 Creating a concentration gradient for sucrose transport into the phloem

Question 4

How is sucrose loaded into the phloem? (3)

Answer 4

1 Hydrogen ions move back into companion cells via co-transport proteins

2 Bringing sucrose with them

3 Which then diffuses into the sieve tubes

Question 5

How does water move into the phloem during translocation? (3)

Answer 5

1 The increased sucrose concentration in the sieve tubes lowers the water potential

2 Causing water to enter from the xylem by osmosis

3 Increasing the pressure inside the sieve tubes

Question 6

How do solutes move from source to sink? (2)

Answer 6

1 Water carrying solutes moves down the sieve tubes from higher pressure at the source to lower pressure at the sink

2 Where solutes are unloaded and used

Question 7

What evidence supports the mass flow hypothesis? (3)

Answer 7

1 Radioactive tracers show labelled carbon dioxide from photosynthesis in the phloem

2 Ringing experiments removing phloem cause sugars to accumulate above the ring

3 Aphids leave mouthparts in plant stems and sap flows faster near the leaves showing a pressure gradient

Question 8

What evidence contradicts the mass flow hypothesis? (3)

Answer 8

1 Not all solutes move at the same rate

2 Sucrose moves to all parts of the plant equally not faster to areas with low concentrations

3 The role of sieve plates is unclear as they could impede flow