3. Which statement describes a difference between the nitrogen and carbon cycles?
a. The carbon cycle involves only plants.
Ob. The nitrogen cycle requires a process
called nitrogen fixation that is carried out by
certain bacteria.
O c. The carbon cycle requires freezing
temperatures.
d. The nitrogen cycle occurs entirely in
the ocean.

a.

Explanation:

The carbon cycle involves only plants. The nitrogen cycle requires a process called fixation, which makes the nitrogen more usable for living organisms. The carbon cycle requires that temperatures be above 27 °C (80 °F).

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the answer that best describes the relative refractory period in the neuron is the resting membrane potential is restored, but concentrations of sodium and potassium are not restored to their original state.

the refractory period is the time during which another stimulus given to the neuron will not lead to a second potential. thus, because na+ channels are inactivated during this time, additional depolarizing stimuli do not lead to new action potentials.  

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