Qualification > Sciences
Biology Paper 1 and 3 help HERE ONLY!!!
hmh:
--- Quote from: zainy on June 07, 2009, 04:16:24 pm ---Thanks a lot ! :)
+ rep 4 u ;)
--- End quote ---
Ur welcome n thx :)
sarcasm:
By the way... what are the decay products when bacteria act on dead organisms?
do they release Nitrogen gas, or ammonium compounds?
nid404:
--- Quote from: sarcasm on June 07, 2009, 04:26:07 pm ---By the way... what are the decay products when bacteria act on dead organisms?
do they release Nitrogen gas, or ammonium compounds?
--- End quote ---
nitrogen gas
Malak:
Can anyone help me with these questions..
Q:Describe how the structure of Xylem tissue is adapted to its functions And the Mechanism of water movement through Xylem.
Q:How blood provides suitable conditions for the reproduction of viruses.
hmh:
--- Quote from: ang3l on June 07, 2009, 04:28:55 pm ---Can anyone help me with these questions..
Q:Describe how the structure of Xylem tissue is adapted to its functions And the Mechanism of water movement through Xylem.
Q:How blood provides suitable conditions for the reproduction of viruses.
--- End quote ---
The tracheids, fibres, and vessels present in the xylem, become lignified during development, losing their living contents. This makes the tissue impermeable (to water) so none is lost as water is transported via the xylem. The tracheids' bordered pits allow for the rapid movement of water from cell to cell.
As is with tracheids, the lignification of vessels can occur as rings, spirals, scalariform or reticulate. In the first formed xylem, rings and spirals occur more frequently. This allows for a limited amount of stretching which may occur in young structures.
Both tracheids and vessels provide a pathway for the transportation of water, whilst also contributing to support.
Hope tht helps!
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