Answer:
In thermodynamics, a closed system can be described as a system which can exchange energy from outside but matter cannot be transferred from such a system. This means that the resources present on the Earth cannot be transferred or replaced and the waste can also not be removed. By understanding the concept of the closed system, humans should recognize the fact that many resources such as minerals present on the Earth cannot be replaced and hence, resources should be utilized effectively in a conserved manner. Also, as waste cannot be removed hence humans should stop forming such waste products which cannot be removed or recycled. 
 
        
             
        
        
        
They do lower the activation energy but they provide an alternate pathway for the reaction to happen quicker and they do not get used up in the reaction
        
             
        
        
        
The main concept of cell theory is that cells are the basic structural unit for all organisms. ... Living things may be single-celled or they may be very complex such as a human being. ... Cells hold a variety of pieces and each cell type has a different purpose. ... The trillions of cells in your body make your way of life possible.
 
        
             
        
        
        
It is macular degeneration