Question

why do all living organisms contain a uniform amount of carbon-14?
match the words in the left column to the appropriate blanks in the sentences on the right.
nitrogen
the continuous formation of -14 in the atmosphere and its continuous decay back to
oxygen -14 produces a nearly constant equilibrium concentration of atmospheric
carbon -14. that -14 is oxidized to carbon dioxide and then incorporated into plants by
photosynthesis. it is also incorporated into animals because animals ultimately depend on plants for
food (they either eat plants or eat other animals that eat plants). consequently, all living organisms
contain a residual amount of -14.
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Explanation:

To solve this, we analyze the carbon - 14 cycle. Carbon - 14 is formed from nitrogen - 14 in the atmosphere (cosmic ray interactions: $^{14}_{7}\text{N}+^{1}_{0}\text{n}
ightarrow^{14}_{6}\text{C}+^{1}_{1}\text{H}$) and decays back to nitrogen - 14 ($^{14}_{6}\text{C}
ightarrow^{14}_{7}\text{N}+^{0}_{ - 1}\text{e}$). The first blank in “formation of _ - 14” should be carbon (since we are talking about carbon - 14 formation). The second blank “decay back to _ - 14” is nitrogen (as per the decay reaction). The third blank “atmospheric _ - 14” is carbon. The fourth blank “That _ - 14” is carbon (referring to the atmospheric carbon - 14). The last blank “residual amount of _ - 14” is carbon.

Answer:

1. The continuous formation of $\boldsymbol{\text{carbon}}$ - 14 in the atmosphere and its continuous decay back to $\boldsymbol{\text{nitrogen}}$ - 14 produces a nearly constant equilibrium concentration of atmospheric $\boldsymbol{\text{carbon}}$ - 14. That $\boldsymbol{\text{carbon}}$ - 14 is oxidized to carbon dioxide and then incorporated into plants by photosynthesis. It is also incorporated into animals because animals ultimately depend on plants for food (they either eat plants or eat other animals that eat plants). Consequently, all living organisms contain a residual amount of $\boldsymbol{\text{carbon}}$ - 14.