Structure + functions of the phloem

Question 1

What is the function of the phloem?

Answer 1

Transports sugars + amino acids to cells which are needed for respiration + synthesis

Question 2

What are phloem cells composed of?

Answer 2

Sieve elements cells which connect to form a tube, which are the main transporting elements

Question 3

What do connecting sieve cells share?

Answer 3

A highly perforated sieve plate, which lets phloem contents flow through

As pores appear in these walls, vacuole membrane, nucleus, + other organelles break down

Mature phloem has no nucleus

Question 4

What is the role of companion cells?

Answer 4

Link with sieve tube elements, linked through many plasmodesmata

Maintain nucleus + organelles, companion cells are very active

Function as ‘life support system’ for sieve tubes, which have lost normal cell functions

Question 5

Why does the phloem structure include high mitochondrial density?

Answer 5

To provide energy from ATP to meet high energy demands of active transport processes involved in loading + unloading sugars to + from sieve tubes elements

Question 6

What is the evidence for mass flow?

Answer 6

• Carbon tracing = ha radioactive sucrose within phloem
• Ringing experiment = Ring of bark removed, area above swells (accumulation of sugars) as phloem transport is stopped, however below doesnt, not being transported upwards