Compare and contrast xylem and phloem.?

Question

Needing help for a bio test, thanks

I also need help including substances transported by each, the direction of movement of each, and the types of cells comprising each.

Answer 1

The xylem transports sap from the root up the plant. Xylem sap consists mainly of water and inorganic ions, although it can contain a number of organic chemicals as well. This transport is not powered by energy spent by the tracheary elements themselves, which are dead at maturity and no longer have living contents. Two phenomena cause xylem sap to flow:

Transpirational pull: the most important cause of xylem sap flow, is caused by the evaporation of water from the surface mesophyll cells to the atmosphere. This transpiration causes millions of minute menisci to form in the cell wall of the mesophyll. The resulting surface tension causes a negative pressure in the xylem that pulls the water from the roots and soil.
Root pressure: If the water potential of the root cells (usually due to high concentrations of solute) is more negative than the soil, water can move by osmosis into the root. This may cause a positive pressure that will force sap up the xylem towards the leaves. In extreme circumstances the sap will be forced from the leaf through a hydathode in a phenomenon known as guttation. Root pressure is most common in the morning before the stomata open and cause transpiration to begin. Different plant species can have different root pressures even in a similar environment; examples include up to 145 kPa in Vitis riparia but around zero in Celastrus orbiculatus

--> http://en.wikipedia.org/wiki/Xylem


Phloem tissue consists of less specialised and nucleate parenchyma cells, sieve-tube cells, and companion cells (in addition albuminous cells, fibers and sclereids). The sieve-tube cells lack a nucleus, have very few vacuoles, but contain other organelles such as ribosomes. The endoplasmic reticulum is concentrated at the lateral walls. Sieve-tube members are joined end to end to form a tube that conducts food materials throughout the plant. The end walls of these cells have many small pores and are called sieve plates and have enlarged plasmodesmata.

The survival of sieve-tube members depends on a close association with the companion cells. All of the cellular functions of a sieve-tube element are carried out by the (much smaller) companion cell; a typical plant cell, except the companion cell usually has a larger number of ribosomes and mitochondria. This is because the companion cell is more metabollically active than a 'typical' plant cell. The cytoplasm of a companion cell is connected to the sieve-tube element by plasmodesmata.


[edit] Function
Unlike xylem (which is composed primarily of dead cells), the phloem is composed of still-living cells that transport sap. The sap is a water-based solution, but rich in sugars made by the photosynthetic areas. These sugars are transported to non-photosynthetic parts of the plant, such as the roots, or into storage structures, such as tubers or bulbs.

--> http://en.wikipedia.org/wiki/Phloem

Answer 2

Basically
Xylem - carries water & minerals in an upward direction through the stems and leaves. It is composed of trachieds & vessel cells.
In common large diciduous trees, xylem is called "wood", and forms
annual rings, which can be seen in a cut tree trunk.
Phloem - In typical large woody trees, phloem is located around the periphery of the tree just beneath the bark. It is composed of sieve tubes & companion cells. It carries food (sap) mostly downward from the leaves to the roots. The phloem can be "tapped" to collect sap for the production of various substances; syrup, rubber, terpentine, etc.