7.9 investigating transport in plants

Question 1

describe the use of ringing experiments to investigate transport in plants

Answer 1

• protective layer and phloem removed
• above the ring swells
• below withers and die
• conclusion: phloem not xylem is responsible for translocating sugars in plants

Question 2

describe the use of tracer experiments to investigate transport in plants.

Answer 2

• grown in an 14CO2 atmosphere incorporating 14C into the sugars
• traced in plant using autoradiography
• place x-ray film under section of plant
• black areas where 14C is present, rest is white

Question 3

explain the evidence that translocation of organic molecules occurs in the phloem.

Answer 3

• when phloem is cut, a solution of organic molecules flow out
• plants provided with radioactive CO2 can be shown to have 14C in phloem
• aphids can be used to extract contents in sieve tubes which show daily variation in the leaves which is mirrored later in the phloem
• ring of phloem from around the whole circumference leads to accumulation of sugars above the ring and their disappearance from below it