What comprises the middle layer of healthy soil, between the top and base layers?
A) only recently eroded rock
B) only decomposing animal wastes
C) only dead plants, animals, and other organisms
D) a mixture of eroded rock and decaying matter
D
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For water to vaporize
A. energy must be supplied. B. energy must be released. C. hydrogen bonds are broken. D. both energy must be supplied and hydrogen bonds broken. E. both energy must be released and hydrogen bonds broken.
With which of the following chemicals do
white blood cells communicate with each other?
a. complement proteins b. cytokine c. hydrogen peroxide d. methicillin e. lysozyme
An organism in an ecosystem that feeds off others is a(n) ____
a. heterotroph b. producer c. autotroph d. photosynthetic organism e. plant
The vertebrate kidney helps to keep the acidity of body fluids constant by varying the amount of hydrogen ions (H+) it secretes into the urine. You can confidently predict that this aspect of kidney function will be controlled by
A) a positive feedback mechanism. B) a negative feedback mechanism. C) nerve impulses from the brain. D) a hormone produced in the kidney itself.