QUESTION

Bill Williams wewilliams at OSPREY.SMCM.EDU
Fri Jul 9 10:33:35 EST 1999


I would love to hear a definitive answer to this question; my
introductory-biology students ask similar questions frequently.  Here's my
answer:

Toxic metabolic products arise because the food that organisms consume
doesn't precisely match the organisms' needs.  Urea is an excellent
example:  heterotrophs necessarily consume complete organisms, or at least
complete cells, but the ratio of calories to nitrogen *in* organisms is
much, much lower than the ratio of calories to nitrogen *needed* in food.
Thus, they have a constant excess-nitrogen problem and excrete urea (or
uric acid, or ammonia, or some other nitrogenous waste).  But the world of
autotrophs is completely different:  they obtain energy from the sun (which
creates is own problems and gives rise to numerous metabolic pathways for
dissipating excess energy) and materials from the air and soil solution.
In general, such organisms simply don't take in materials that they don't
need, or at least that they cannot use without poisoning themselves.

So:  if you don't want to bother with kidneys and livers, don't eat!

-W2

At 08:54 -0700 7/9/99, Santosh Baburao Mane wrote:
> I am pharmacy student , we study about plants ,and use of plant as
>sources of drugs
>
> So my question is," why plants are able to survive with out excretory
>system that is  kidney or liver
>like organs ???" They do not need detoxification ?? why metabolic products
>are not able to give toxicity
>to plant and why they induced toxicity to animal cells only .
>  plants cells having any mechanism  for detoxification or is it
>natural???
>
>So pl help me to finding out answer  of this
>
>
>pl mail me ans.
>
>Thanks
>Santosh
>San_dha at giaspna.vsnl.net.in


________________________
William E. Williams
Biology Department
Saint Mary's College of Maryland
18952 E. Fisher Rd.
Saint Mary's City, MD  20686-3001
(301)862-0365

Summer:  Botany  Department
	 Aven Nelson Building
	 University of Wyoming
	 PO Box 3165
	 Laramie, WY 82071-3165
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