Answer:
Oxygen is moved around the body of an echinoderm in its C. water vascular system.
 
        
             
        
        
        
As viruses cannot reproduce by themselves, they depend on the host cells that they infect to reproduce
        
                    
             
        
        
        
Answer:
fruit weight
Explanation:
In an experiment, the dependent variable is the variable that responds to the changes made to the independent variable. In other words, the dependent variable, as the name implies, is DEPENDENT on another variable called independent variable. The dependent variable is the variable that is measured or recorded by the experimenter during the experiment. 
In this case where a student is studying the effect of fertilizer on fruit growth. He uses 6 tomato plants, which were given different concentrations of fertilizer (independent variable). After the experiment, the weight of the tomato fruit were measured. This means that the FRUIT WEIGHT is the dependent or responding variable. 
 
        
             
        
        
        
Answer:
A scientific model is a representation model for a certain scientific concept. Scientific models make it easier to study a phenomenon as they tend to model out the exact phenomenons. 
A drawing of an skeleton would be unclear as the children might not be able to locate certain features in the drawing. For example, a certain joint could be missed by the teacher in the drawing or the child might not exactly be able to locate where the joint or bone is present.
But as the model will be more real to the actual skeleton system hence, studying through a skeleton will make it a lot easier to study the human skeletal system.