Structure and function of the xylem and phloem Flashcards
What is the structure of xylem?
mainly consists of dead cells
columns of dead cells that are reinforced with lignin to provide support
lignin keeps the column open even when the water supply is low because the column has a tendency to close, spiral maintains flexibility
water leaves the xylem through unlignified areas called bordered pits
What is the function of the xylem?
transport water and mineral ions
flow of materials is up from the roots to the shoots and leaves
What are sieve tubes and plates?
living tissue
main transporting vessels are the sieve tube elements
made up of cells join end to end to form a hollow structure
in areas between cells, the walls become perforated to form sieve plates which look like sieves and the let the phloem contents flow through
large pores appear in the cell walls, the tonoplast (vacuole membrane), the nucleus and some other organelles break down
the phloem becomes a tube filled with phloem sap and the mature phloem cells have no nucleus
What is the function of phloem?
transports food in the form of organic solutes around the plants from the leaves where they are made in photosynthesis
supplies cells with sugar and amino acids need for cellular respiration and for the synthesis of other useful molecules
can go either up or down
What are companion cells?
form with sieve tube elements
linked with them via plasmodesmata
maintain nucleus and other organelles
very active cells that function as a life support system for the sieve tube cells which have lost most of their normal functions
Wgat are sclerids?
supporting cells with extremely thick cell walls
also have fibres
How is the structure of xylem cell wall different from root hair cell wall?
thicker and lignified
What two types of cell are found in phloem tissue?
sieve tube elements
companion cells
How are substances transported out the xylem and the phloem?
xylem - bordered pits
phloem - plasmodesmata
