There are 4 chromosomes that are visible at the beginning of Mitosis.  
        
             
        
        
        
Answer - C
Nonvascular plants do not consist of xylem and phloem and they have their own mechanism of action for transport of water and other nutrients to their cells.
        
                    
             
        
        
        
Trisomy=3 chromosomes; 1 more than the required pair (2)
21=the type of chromosome 
So, here we can eliminate A and B.
Now we have C and D.
I know that when sperm cell(s) simultaneously fertilize [an] egg, a class of identical twins will form. Therefore, we can eliminate D, leaving us with merely C. Henceforth, C is your final answer.
 
        
                    
             
        
        
        
The limitations of cell size are:
1) Surface area to volume ratio 
2) Nucleo cytoplasmic ratio 
3) Fragility of cell membrane 
What are the cause of limitations on cell size?
The need for a surface area of sufficient area to allow the cells function→. 
→If the surface area of cell increase volume increase to the cube of the linear increase. 
→ Nuclie contains information needed for protein synthesis . Some cells reduce this limitation to increase the no. Of nucleus called multinucleated.
Examples are muscle cells.
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