HELP - Phloem and Xylem? (1 Viewer)

[sezzygirl89]

Can some one please explain in simple terms what they both are and what they transport. I so don't get it!

 

[Lucid Scintilla]

Can some one please explain in simple terms what they both are and what they transport. I so don't get it!

Like, hi.

So phloem, unlike xylem, consists of living cells that transport sap; phloem more or less transports organic matter, including saccharides, amino acids, messenger RNA, and certain hormones through sieve tube elements - elongated parenchyma cells.

It does this through diffusion; a high concentration of organic substance inside cells of the phloem at a source, such as a leaf, creates a diffusion gradient that draws water into the cells. Movement occurs by bulk flow; phloem sap moves from sugar sources to sugar sinks by means of turgor pressure.

Xylem - the other tranport tissue in plants; it, unlike the phloem, as I said, is primarily made-up of dead cells - transports water, and dissolved nutrients/ions - in the form of sap - from the roots of a plant. The mechanisms for this are transpiration/transpirational pull and root pressure.
Transpirational pull is caused by the evap. 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; this pressure pulls the water from the roots and soil.
Root pressure works if the water potential of the root cells is more negative than the soil, usually due to high concentrations of solute; through osmosis - you know, moving against the concentration gradient.

Hopefully this helps.

 

[jannny]

Wow Lucid, nice terms in describing how it works. Damn, I wish I can I write like that heh.

Well to make it simple.

Phloem carries the vitamins, amino acids, proteins around the plant. It does this by active transport( Uses energy ).
The theory on the movement of materials in the phloem is called "source to sink theory" or translocation.

Firstly, sugar from the leaf(source) is loaded into the phloem cells. Then water goes into the phloem cells due to osmosis, creating a high pressure at the source end. The mass flow of sugar and water moves into low pressure of the sink e.g. roots, and sugar leaves the mass flow of water and sugar through diffusion( to the roots). The changes in pressure allows sugar to move around the phloem cells.

Xylem carries water around the plant. It uses passive transport

Water enters the roots through osmosis, creating root pressure. Then once water is inside the roots, the water "bundles up" through the property of water called cohesion. The "bundled water" elevated through the tubes of xylem cells through cappilarity (think of it as when you use straw to drink somethin). Then through when water "transpires" in the leaves it creates a "tension pull" to pull the bundled water up to the leaves to replace the lost water through transpiration.

 

[pattii]

in more simple terms

phloem= everthing but water
all directions
xylem=water
only up

 

[Buiboi]

xylem: inorganic substances
phloem: organic substances and photosynthetic products

xylem:
cohesion: water molecules clump together to allow easy water transport
transpiration stream: stream of i like peas water formed as aresult of cohesion and adhesion.
adhesiong: water molecules dont fall down due to gravity but instead stick to the walls.

Phloem:
whatever the others said, the source to sink theory

also the
apoplastic loading: i cant remember this one...but something about going through the cell membrane then the cell wall

symplastic loading: substances move to the cytoplasm by going through the mesophyll cells to the sieve tube/element/? then passed the plasmodesmata.