What possible use could a weed be? Explain how weeds can be useful, starting with your definition of weed
What will be an ideal response?
The 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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Two spheres are made of conducting material. Sphere #2 has twice the radius of Sphere #1 . What is the ratio of the capacitance of Sphere #2 to the capacitance of sphere #1?
a. 1, since all conducting spheres have the same capacitance. b. 2 c. 4 d. 8 e. A single sphere has no capacitance since a second concentric spherical shell is necessary to make a spherical capacitor. Thus, none of the answers above is correct.
A wheel rotating about a fixed axis with a constant angular acceleration of 2.0 rad/s2 starts from rest at t = 0 . The wheel has a diameter of 20 cm. What is the magnitude of the total linear acceleration of a point on the outer edge of the wheel at t = 0.60 s?
a. 0.24 m/s2 b. 0.50 m/s2 c. 0.14 m/s2 d. 0.34 m/s2 e. 0.20 m/s2
If a convex lens were made out of very thin clear plastic filled with air, and were then placed underwater where n = 1.33 and where the lens would have an effective index of refraction n = 1, the lens would act in the same way
a. as a concave mirror in air. b. as a concave lens in air. c. as a convex lens in air. d. as a flat refracting surface between water and air as seen from the water side. e. as the glasses worn by a farsighted person.
The Sun's surface seethes and churns with a bubbling pattern. Why?
A) We are seeing hot gas rising and cool gas falling as a result of the convection that occurs beneath the surface. B) The Sun's surface is boiling. C) The churning gas is being stirred up by the strong solar wind. D) The churning is an illusion created by varying radiation; the gas on the Sun's surface is actually quite still.