Which activities? I want to say the nucleus as it is the control center of the cell, but this is a vague question.
        
                    
             
        
        
        
The addition of acetyl groups to histones is associated with chromatin condensation and and higher levels of gene expression
        
                    
             
        
        
        
The true answer of your question is : 
OH : HYDROXYL GROUP
NH2 : AMINO GROUP
CH3 : METHYL GROUP ( but in rather broader terms, that functional group of formula CnH2n+1 where n is an integer is called ALKYL GROUP where by substituting n by 1,2,3... we obtain methyl for n = 1, ethyl for n = 2, and propyl for n = 3 )
COOH : CARBOXYL GROUP is the correct answer since carbonyl is characterized by the presence of functional group C=O in general the formula of the compound would be 
R-C=O-R’ where R and R’ are alkyl groups like methyl for example. However the carboxyl group could be thought of as a summation of carbonyl + hydroxyl ( CO + OH ) resulting thus in COOH. 
I hope you’ll understand everything, anyway if not i’m always here to help. ♥️
        
             
        
        
        
Gravity is a force which causes objects to fall or be still on the earth's surface. This invisible force has been longed explored mainly by many scientist however, Isaac Newton was first to conceptualize this into a proper principle. 
GravityLight is a device that was recently developed by engineers that is designed to produce light through the force of gravity. 
        
             
        
        
        
Answer:
Selective breeding involves choosing parents with particular characteristics to breed together and produce offspring with more desirable characteristics. Humans have selectively bred plants and animals for thousands of years including: crop plants with better yields.
Explanation:
Hope that helps