The mass of an atom is contained primarily in its NUCLEUS.
An atom is made up of three sub particles, which are proton, neutrons and electrons. The proton and the neutrons are located in the nucleus of the atom while the electron  are located outside the nucleus where they move about in continuous motion around the nucleus. The proton and the neutrons, which are located in the nucleus have the same relative mass of 1, which has been estimated to be about 2,000 times bigger than that of the electron, which has a relative mass of 0.0005. This shows that, the mass of an atom is located primarily in its nucleus. <span />
        
                    
             
        
        
        
Answer:
When light energy is absorbed by a chlorophyll molecule its electrons gain energy and move to higher energy levels in the molecule 
 
        
             
        
        
        
Answer:
MHC Markers
Explanation:
The function of MHC molecules is to display peptide fragments derived from pathogens on the cell surface for recognition by the appropriate T cells.
 
        
             
        
        
        
Answer:
Geologists do not use carbon-based radiometric dating to determine the age of rocks. Carbon dating only works for objects that are younger than about 50,000 years, and most rocks of interest are older than that
Explanation:
 
        
             
        
        
        
Answer: The correct answer for the blank is-
B) Sugar and oxygen.
Explanation:
Cellular respiration can be described a metabolic process that includes the break down of organic molecule like glucose (a carbohydrate or sugar) to form carbon dioxide and water along with large amount of energy in the form of ATP ( adenosine triphosphates), which is used for driving various cellular processes. 
Aerobic cellular respiration involves the presence of oxygen along with glucose. 
Thus, sugar and oxygen, being the reactants in cellular respiration is the right answer.