Answer to Question 1There are such costs, as indicated above. These costs are very similar to the health
costs of comparable jobs such as trash collection.
Answer to Question 2The American Heritage Dictionary says that a weed is a plant considered
undesirable, unattractive, or troublesome. The considered part tells us that a plant may
be considered a weed in one situation and not in another. Ralph Waldo Emerson famously
said a weed is any plant whose virtues have not been discovered. All plants evolved for a
specific purpose in a specific environment, so weed is a human concept, and in many
cases a human-caused occurrence. Biology online characterizes weeds as any plant that is
growing in a place where a human wants a different kind of plant or no plants at all . . .
Plants that are considered a nuisance . . . because they compete for resources in the same
local environment as . . .crops.
Many plants classified as weeds are plants from elsewhere invading new habitat and are
difficult to control because the organisms that evolved to control their spread were left
behind in the plants' original homes. A list of weeds classed as noxious by the Federal
Noxious Weeds Program (APHIS) may be found at the website
http://www.aphis.usda.gov/ppq/permits/noxiousweed_list.html.
As for utility, the genes of weeds can supply information that is used in cultivated plants.
The presence of weeds can divert plant diseases from desirable crop plants. The Pacific
yew, long considered a tree weed, turned out to be a source of taxol, a breast-cancer-fighting
agent. Arabidopsis thaliana, a wild mustard weed, is being used as a model organism in
plant biology studies.
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