In order to increase the rate of diffusion of materials in and out of the cell, the following modification can be done to the cell:
1. the shape of the cell can be changed to one that has high surface area to volume ration, for example sphere.
2.The cell can also divide into two in order to increase the surface area to volume ratio. 
        
             
        
        
        
The natural water sample contains only one type of bacteria.
 
        
                    
             
        
        
        
<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.