The time that it takes for half of a radioactive isotope to change into another stable element is its
A. chemical life cycle.
B. half-life.
C. activation time.
D. life span.
Answer: B
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Which of these time intervals, based on plant fossils, came last (most recently)?
A) extensive growth of gymnosperm forests B) Silurian-Devonian explosion with fossils of plant lineages that contain most of the major morphological innovations C) colonization of land by early liverworts and mosses D) rise and diversification of angiosperms E) carboniferous swamps with giant horsetails and lycophytes
Which structure adjusts to control the intensity of incoming light?
a. cornea b. sclera c. iris d. ciliary body e. fovea
When comparing the sequences of a homologous gene in four different species, one pair of species shows a 1% difference, whereas the other pair shows a 3% difference. Which pair diverged longer ago from their common ancestor and why?
A. The pair with a 1% difference? a smaller difference (1% instead of 3%) indicates that there has been less time to accumulate mutations. B. The pair with a 1% difference? a smaller difference (1% instead of 3%) indicates that there has been more time to accumulate mutations. C. The pair with a 3% difference? A larger difference (3% instead of 1%) indicates that there has been less time to accumulate mutations. D. The pair with a 3% difference? a larger difference (3% instead of 1%) indicates that there has been more time to accumulate mutations.
In the kidney, the collecting ducts from the nephrons empty immediately into the
a. renal cortex. b. renal medulla. c. renal pelvis. d. ureter. e. urethra.