Taxonomy is the science of defining and naming groups of biological organisms on the basis of shared characteristics.
        
             
        
        
        
Chromoplast(Plastid) is the answer you are very welcome
        
             
        
        
        
Eukaryotes are organisms whose cells have a nucleus enclosed within a nuclear envelope.
 
        
                    
             
        
        
        
Explanation:
Psi packaging Element is a cis-acting RNA element identified in the genomes of the retroviruses Human immunodeficiency virus (HIV) and Simian immunodeficiency virus (SIV) It is involved in regulating encapsidation of the retroviral RNA, an essential step in replication.
 
        
                    
             
        
        
        
Answer:
The word that best complete the sentence is VIRUSES.
Explanation:
There are different types of microorganisms, one of them is virus. Viruses are different from other forms of microbes because they need living cells to become active; outside living cells they are inactive and did not exhibit any of the features of living things. 
Viruses only grow and multiply when they are withing the cells of another living thing; they do not have the capacity to survive and reproduce outside a living host.