joelle Posted April 13, 2007 Share Posted April 13, 2007 How does xylem tissue in angiosperms differ from xylem tissue in gymnosperms? Link to comment Share on other sites More sharing options...
ecoli Posted April 13, 2007 Share Posted April 13, 2007 "Primary xylem, also known as Protoxylem, is the xylem that is formed during primary growth from procambium. Secondary xylem, also known as Metaxylem, is the xylem that is formed during secondary growth from vascular cambium. Secondary xylem is also found in members of the "gymnosperm" groups Gnetophyta and Ginkgophyta and to a lesser extent in members of the Cycadophyta. The two main groups in which secondary xylem can be found are: 1. conifers (Coniferae): there are some six hundred species of conifers. All species have secondary xylem, which is relatively uniform in structure throughout this group. Many conifers become tall trees: the secondary xylem of such trees is marketed as softwood. 2. angiosperms (Angiospermae): there are some quarter of a million to four hundred thousand species of angiosperms. Within this group secondary xylem has not been found in the monocots. In the remainder of the angiosperms this secondary xylem may or may not be present, this may vary even within a species, depending on growing circumstances. In view of the size of this group it will be no surprise that no absolutes apply to the structure of secondary xylem within the angiosperms. Many non-monocot angiosperms become trees, and the secondary xylem of these is marketed as hardwood." from http://en.wikipedia.org/wiki/Xylem Link to comment Share on other sites More sharing options...
joelle Posted April 13, 2007 Author Share Posted April 13, 2007 i read thatt already, but thankss soo much i still dotn get it its only worth 2 marks i was told that in one, when corsssectioned, the xylem is arranged in a circle in the other they're scattered is that truee? and if soo which one are they scattered Link to comment Share on other sites More sharing options...
ecoli Posted April 13, 2007 Share Posted April 13, 2007 The xylem in angiosperms are more fibrous and thicker then their gymnosperm counterparts. Hence why there trunks tend to be thicker and woodier. There's more lignan in the cell walls of the xylem. Link to comment Share on other sites More sharing options...
joelle Posted April 13, 2007 Author Share Posted April 13, 2007 thank you so much! i was freakingg out lol =) Link to comment Share on other sites More sharing options...
ecoli Posted April 13, 2007 Share Posted April 13, 2007 thank you so much!i was freakingg out lol =) haha... relax, guy. (or gal) Link to comment Share on other sites More sharing options...
joelle Posted April 13, 2007 Author Share Posted April 13, 2007 this sitee is cool lol im so glad i found it. i have some more questionss but im trying to figure them outt! you'll probally hear from me againn:cool: loll Link to comment Share on other sites More sharing options...
joelle Posted April 13, 2007 Author Share Posted April 13, 2007 Mature phloem cells lack a nucleus. If the nucleus is the control center of the cell, how are there cells controlled? i dont get that question wouldnt it just not function withoutt a nucleusss? im lost Link to comment Share on other sites More sharing options...
joelle Posted April 13, 2007 Author Share Posted April 13, 2007 a. Sieve-tube cells lack a nucleus, are arranged end to end and have channels in end walls (thus, the name "sieve-tube") through which plasmodesmata extend from one cell to another. b. Companion cells connect to sieve-tube cells by numerous plasmodesmata, are smaller and more generalized than sieve-tube cells; they have a nucleus. is that right? like about how they connect to compannion cells who have a nucleus? Link to comment Share on other sites More sharing options...
ecoli Posted April 13, 2007 Share Posted April 13, 2007 yes, the companion cells direct the genetic requirements of the xylem. Link to comment Share on other sites More sharing options...
joelle Posted April 13, 2007 Author Share Posted April 13, 2007 thank youuuu for the second time lol Link to comment Share on other sites More sharing options...
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