Explain why xylem and phloem together can be considered to be transport systems.?

Question

Once again I am having trouble comeing up with these answers.

Explain why xylem and phloem together can be considered to be transport systems.

Thanks in advance.

Answer 1

Transport in Plants:
Absorption of water and minerals by roots: Water and mineral enter through root epidermis, cross the cortex, pass into the stele, and are carried upward in the xylem.
Active accumulation of Mineral Ions. The cells cannot get enough mineral ions from the soil by diffusion alone. The soils solution is too dilute.
ACTIVE TRANSPORT of these ions must occur. Specific carrier proteins in the plasma membrane attract and carry their specific mineral into the cell. A Proton Pump: H+ is pumped out of the cell causing a change in pH and a voltage across the membrane. This helps drive the anions and cations into the cell. Water and minerals cross the cortex in one of 2 ways: Via SYMPLAST which is the living continuum of cytoplasm connected by PLASMODESMATA. Via APOPLAST which is nonliving matrix of cell walls. At the endodermis the apoplastic route is blocked by the CASPARIAN STRIP. this is a ring of suberin around each endodermal cell. Here water and minerals MUST enter the stele through the cells of the endodermis. Water and minerals enter the stele via symplast, but xylem is part of the apoplast. Transfer cells selectively pump ions out of the symplast into the apoplast so they may enter the xylem. This action requires energy.

ASCENT of XYLEM SAP:
Water transported up from the roots must replace water lost by transpiration.

WATER POTENTIAL: Xylem sap rises against gravity, driven by a gradient of water potential (*) Water flows from an area of high * to an area of low *. Water Potential is expressed in units of pressure: 1 bar = pressure needed to push a column of water up 10 meters. 1 megapascal= 10 bars. Pure water has * = 0. Addition of pressure increases *. Addition of solutes decreases *.
ROOT PRESSURE: When transpiration is low, ions pumped into the stele decrease * and cause water uptake by the stele. This uptake force is called root pressure. Cannot keep pace with transpiration, can force water up only a few meters.

TRANSPIRATION-COHESION-ADHESION THEORY:
a). water leaves leaf through stomata.
b). this water loss is replaced by evaporation from mesophyll cells, lowering their water potential, causing them to take water from neighboring cells.
c). Process continues back to the tracheids causing water up take from the xylem sap.
d). Water goes fro tracheids to air following a water potential gradient.
e). Cohesion and adhesion of water. H bonds of water, hydrophilic walls of xylem and small diameter of xylem aid in the movement of water up the tube.
f). This pull decreases water pressure in the xylem causing the roots to take water from the soil.

How Stomata Open and Close:
Turgid guard cells open the stomata, while flaccid cells close them.
The K+ ion is responsible for the stomatal action.
Uptake of K+ causes the cell to become turgid- decreases water potential.
Stomata open at dawn because light induces the cells to take in K+. An internal clock (circadian rhythm) will make them open even if in they are kept in the dark.
Guard cells will close due to: a water deficiency, High temperatures due to an increase of CO2


Transport in PHLOEM:

Translocation = transport of the products to the rest of the plant by the phloem. Phloem carries sucrose, minerals, amino acids, and hormones.

SOURCE to SINK TRANSPORT:

Source = origin of the sugar Sink = Organ that consumes or stores the sugar.
Flow is always from the source to the sink.
Phloem is loads by active transport.

Answer 2

Both of them are interdependent in transporting and distributing water, mineral and food. Phloem is primarily responsible for translocation or distribution of food [sucrose] from photosynthesis to the rest of the plant organs. Xylem is responsible for transporting water and mineral throughout the plant. The movement of those molecules [food, mineral and water] are dependent of the osmolarity of the contents within the xylem and phloem [collectively known as the vascular bundle] because they both are channels which transport molecules within the plants.

Answer 3

Xylem carries or transports water and dissolved minerals.
Phloem carries or transports food (glucose).

Answer 4

well xylem transports water and phloem transports sugar so two processes make a system i suppose

Answer 5

The answer can be found in any Plant anatomy book,supplemented by Plant physiology book.

Or click on the links below--

1) http://en.wikipedia.org/wiki/Xylem

2) http://en.wikipedia.org/wiki/Phloem

3) http://www.google.co.in/search?hl=en&q=+Xylem&btnG=Google+Search&meta=

4) http://www.google.co.in/search?hl=en&q=Phloem&btnG=Search&meta=