Plants:
1. Most plants respond to the environment by growing towards the light.
2. Plants respond to daily and seasonal cycles and diseases.
Flatworms:
1. Flatworms respond to changes in light.
2. Flatworms adapt to marine life by using diffusion to breathe and to distribute nutrients to other parts of the body.
Humans:
1. The nervous system allows an organism to respond quickly to changes in the internal or external environment.
2. Some humans modify the environment (positively or negatively), such as cutting forests, building dams, and expanding urban areas, etc.
 
        
             
        
        
        
Answer:
Isometric contraction
Explanation:
The length of the muscle is changed during contraction only when the muscle tension during contraction can outstand the resistance exerted by the object to be lifted.  
During isometric contractions, the muscle tension is not sufficient to exceed the resistance of the object. Hence, there is no change in the length of the muscle. The isometric contraction does not bring about any body movements.  
 
        
             
        
        
        
I would say the first one a comet. :)