Answer: summation
Explanation:
The process which determine if an action potential will be generated or not depends on the combined effects of the signal inputs from multiple sources of  synapse or from the repeated signals from the same synapse.  
If the input signals reach the threshold voltage, action potential will be generated. (all –or –none principle).Therefore, this  process is a determinant of  the likelihood of action potential generation  and it is called summation.
Summation is the ability to integrate multiple PSPs at multiple synapses.it is  the process that determine if an action potential will be generated by combined effects of inhibitory or excitatory  signals.
Based on the pathways and voulme of applied stimuli in the presynaptic neuron;
The signals can be temporal summation ( consecutive  signals  produced from the same  synapse)where action potential of high frequency in the PSN generated action potential in the post synaptic neuron, which summate with one another. Or Spatial where signals inputs are from multiple presynaptic cells.
 
        
             
        
        
        
Two factors infuence the regions photosynthetic productivity which would be the amount of solar radiation and the availability of nutrients because solar radiation is needed as well as nutrients which keeps the plant healthy 
hope this helps (:
        
             
        
        
        
DNA can illustrate that evolution has occurred since in the process of natural selection advantegeous genes or traits have been selected to pass on through generations and further more evolve as long as the species survies and is successful in reproducing.