<span>Formation of bivalents lead to spindle fibers from opposite poles attaching to homologous chromosomes.
Hope this helps!!</span>
        
             
        
        
        
Answer:
There is a higher oxygen content in the air of the lungs than that of oxygen-depleted blood and a lower carbon dioxide concentration. This gradient of concentration causes gas exchange during respiration.
Explanation:
 
        
             
        
        
        
 In physical science there are two types of "isolated systems"
1. Being a Physical System in which it is so far removed from other systems that it does not react with any of them.
2. Being a Thermodynamic System in which it is enclosed by rigid immovable walls of which neither mass nor energy can flow through.
I believe in this case although not stated that it would refer to a Thermodynamic System which would leave you with the only plausible answer as ENERGY AND MATTER CANNOT ENTER OR LEAVE.
None of the other answers make sense. Even if it were referring to Physical. Physical does not react with anything at all. An as you can see Thermodynamic does not allow for anything to pass through or leave.
 
        
                    
             
        
        
        
Answer:
C.) The oxygen produced by photosynthesis during the day is greater than the amount of oxygen used for respiration.
Explanation:
Oxygen concentration decreases at night.Concentrations of oxygen can decrease significantly during the night, due to respiration. DO concentrations are usually highest in the late afternoon, because photosynthesis has been occurring all day.