Lesson 11.2 - Phloem Flashcards
Phloem definition:
Living tissue that transports food in the form of organic solutes around the plant from the leaves where they are made in photosynthesis.
What does the phloem supply cells with?
amino acids and sugar
Main transporting vessels in phloem?
sieve tube elements
How are sieve tube elements organised?
Like xylem, made up of many cell ends joined end to end to form a long, hollow structure.
Difference between xylem and phloem structure?
Cells are not lignified.
How are sieve plates formed?
In areas between cells, the walls become perforated.
What do sieve plates do?
Let the phloem contents flow through.
Vacuole membrane name?
Tonoplast
What happens when large pores appear in cell walls?
tonoplast, nucleus and some other organelles break down.
Phloem becomes a tube filled with phloem sap and the mature phloem cells have no nucleus.
What are closely linked to sieve tube elements?
Companion cells
What is a plasmodesmata?
microscopic channels through the cellulose cell walls linking the cytoplasm of adjacent cells.
What do the plasmodesmata do in sieve tube elements and companion cells?
Connect them
What do the companion cells do?
Maintain nucleus and all other organelles.
Very active and it is thought that they serve as a ‘life support system’ for the sieve tube cells.
Supporting tissues in phloem tissue?
- fibres
- sclereids
What are sclereids?
Cells with extremely thick cell walls.
