Marine biologists study changes in the ocean. so they will look at the chemical composition of deep waters and see how consecrated the oxygen is. They will also study the movements of the plates because when planted move it usually makes new food for deep life
they will also check animal concentrations in certain areas. 
Another thing they do is track animal movements. this could be by putting a tracker on a whale or a shark or anything and watching its depths it goes or watching the distance it goes in a day.
        
                    
             
        
        
        
Answer:
Explanation:
Around every blood vessel 
 
        
             
        
        
        
The tennis ball. Because of less mass
        
                    
             
        
        
        
Tigers are a very important part of the food chain, but sadly they are going extinct. Their habitats are being destroyed, forcing the tigers to kill farmers livestock. In some countries tigers are still used for medicinal purposes, so they are often hunted for their teeth and pelts. Tigers may not seem important but they play a very important part on the food chain. Without these tigers the population of boars and other prey would sky-rocket and that would not be good for the environment. 
        
             
        
        
        
I think this would answer your question. I did this in school and I only got a few wrong....