The CNS involves the brain and spinal cord and the PNS involves the body nerves.
<u>Answer</u>: an all or none response
According to the all-or-none law, it a certain threshol is crossed by a stimulus' strenght, it will cause a response in the nerve cell or muscle fiber. However, the strenght of the response will always be the same and will not vary with different stimulus strengths. The only requirement is for the threshold to be crossed.
Carbon dioxide, or CO2.
Plants produce oxygen for us to breathe, and in exchange they take the gas we breathe out: carbon dioxide.
