The hormone calcitonin, which is produced by the parafollicular or C cells of the thyroid, has the opposite effect on blood calcium levels as does PTH. I hope this helps! : )
        
                    
             
        
        
        
Answer:
A = Activator
B = Effector
Explanation:
An activator is a protein which typically binds to a short (50–1500 bp) region of DNA which might be located either upstream (mainly) or downstream of a gene so as to cause increased transcription. This particular region of DNA is known as enhancer and activator is also  known as transcription factor. Activator is a trans-acting factor which binds to the cis-acting factor which is enhancer so as to enhance transcriptional expression. 
But another protein named as effector may restrict activator from binding to the enhancer leading to a decrease in transcriptional expression by binding to the activator allosterically. Allosteric binding of effector to the activator causes conformational change in activator so it can no longer bind the enhancer. 
 
        
             
        
        
        
Answer:
2, 6 are the one you should select
Explanation:
 
        
             
        
        
        
Answer:
D) Only cells containing Mitochondria can reproduce.
 
        
             
        
        
        
Answer:
Fixation of oxygen occur instead of carbondioxide.
Explanation:
If the stomata remain closed due to water loss, the concentration of carbondioxide decreases and oxygen increases in the leaf because of the fixation of oxygen instead of carbondioxide by rubisco. The plant takes carbondioxide from the atmosphere when the stomata is open so when the stomata is closed there is no other way for getting carbondioxide into the leave so the oxygen is now being fixed by our rubisco enzyme to that five-carbon compound instead of carbon dioxide.