Why are gills typically external and lungs typically internal? ( you may enter up to 150 characters. ) your answer?

The gills are external because their main function is to extract dissolved oxygen from water. The external location of gills also prevents the entry of extra water inside the body. Entry of excess water may disturb the osmotic balance of the organism which may result in death.

In contrast, lungs are internal as they extract oxygen from the air and their function depends on atmospheric pressure. If the lungs would be external it would be difficult to change the pressure inside the lungs which helps in gas exchange.  

In addition, the lungs are needed to be moist, they are very delicate and soft. So, the external location would cause infection, damage, and loss of function of lungs.

i believe the correct answer from the choices listed above is the first option. the scientists need to look at the   validity of data, claims, hypotheses, and observations before  developing an argument. they base their arguments on facts that are present and they make sure they have proofs. 

explanation:

the answer would be 2, if crossing over doesn’t occur 2 out of 4 of the daughter cells will have that allele.

hope this : )