What process evolved around 2.3 billion years ago that introduced significant amounts of free oxygen to the atmosphere?
a. formation of iron oxide (rust)
b. endosymbiosis
c. aerobic metabolism
d. radiometric dating
e. water-based photosynthesis
Ans: e. water-based photosynthesis
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Which of the following pathways are composed of the axons of neurons with their cell bodies in the brain stem
a) spinothalamic b) rubrospinal c) spinocerebellar d) corticospinal
If something in the environment controls a population level and is uninfluenced by the population size, it is known as
A. a biotic factor. B. a density-dependent limiting factor. C. a density-independent limiting factor. D. None of these answers is true.
From what kind of molecules are steroid hormones made?
What will be an ideal response?
Glass is a solid that is not crystalline, but rather an ____ solid.
What will be an ideal response?