The function of the somatic nervous system includes all nerves controlling the muscular system and external sensory receptors.
        
                    
             
        
        
        
The stomata of leaves are surrounded by guard cells. The guard cells help the leaves to regulate the rate of transpiration of water from the leaves by opening and closing the stomata. When water enter the guard cells, they swell and bulge and this makes the stomata to open. So, with high water pressure, the guard cells will stimulate the stomata to open. The reverse will be the case if the water pressure is low.
        
             
        
        
        
B, for sure. Producers, Like grass and Flowers need water to make food. Consumers, like Cats, Snakes and Boars need water to drink so our internal systems will function properly. 
Im not sure if decomposers need water, but if there is less water then more animals die and they get food. so, not sure about that one.
        
                    
             
        
        
        
A macrophage is a large phagocytic cell that engulfs foreign particles and pathogens. So Macrophage. 
Hope this help! :)