late posts.
golly i'm behind. i really have to study for biology too. i am dead.
well.. no turning back.. must press on. notes time.
as we know, xylem and phloem are the transport systems in plants. today we got into detail.
XYLEM
they are single-cell thick tubes. how it starts is its a column of cells, and the tops and bottoms dissolve leaving a tube. xylem is made of dead cells.
PHLOEM
they're living cells. they're not exactly hollow tubes, instead of the tops and bottoms of the cells dissolving completley, they have holes and are hence known as sieve cells. since they're living, they need to function, but have no nucleus, so phloem cells have companion cells to do metabolizing for them.
xylem and phloem are always adjacent, so that water can diffuse from the xylem to the phloem as necessary to transport organic material. the process uses active transport, which means it spends energy to do this. it's all diffusion until the concentrated sugar (from the source, normally leaves) until gets to the sink (target, anywhere)
umm.. i think thats all to say, unless i remember later
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