Mitochondria and chloroplasts likely evolved from engulfed bacteria that once lived as independent organisms. ... Eukaryotic cells containing mitochondria then engulfed photosynthetic bacteria, which evolved to become specialized chloroplast organelles.
The answer is prokaryotes
 
        
             
        
        
        
Answer:
This happens because of our immune system. Our immune system keep record of every attacking microbe. It contains two type of while blood cells firstly is T cell that respond quickly to the attacking microbe. While secondly B cells that recognize those specific cells and fights them off. In addition to that B cells clones itself as memory cells for that disease and will remains in your body for years
 
        
             
        
        
        
Answer: unfavourable ph condition for the pepsin
Explanation: during digestion, enzymes are needed to aid the process.digestive enzymes are biological catalyst that breakdown large food particles into digestible form .
As biological catalyst, enzymes require an optimum temperature and pH condition.outside this temperature or pH,the enzyme is denatured.
In the stomach, hydrochloric acid is required to convert pepsinogen into it's active form,pepsin.the acid also creates an optimum low pH that pepsin needs to function.
As the food moves to the small intestine,the pH is alkaline and is unfavourable for pepsin to function.