Answer:
Like the plasma membrane, organelle membranes function to keep the inside "in" and the outside "out."
Explanation:
 
        
             
        
        
        
The rotation of the earth around the sun
        
                    
             
        
        
        
When a single copy of a disease allele doesn't result in a disease but instead is good for the person or organism that carries it, we say that allele has a heterozygote advantage. In other words this occurs when heterozyhotes have increased fitness over both homozygotes.  A good example is sickcle cell trait, which protects against malaria in heterozygotes, but causes a deadly disease in homozygotes. 
        
             
        
        
        
A selective permeable membrane is a membrane but it only allows some things to go through and not others.