Why does the eggs covering change after sperm has entered the egg?

Found evidence that the continents were joined together at one time.

The carbon cycle is best defined as a process in which a. carbon changes from inorganic forms to organic forms and back b. carbon is changed into other elements such as oxygen or nitrogen c. carbon is continually created from the sun’s energy by plants d. carbon is consumed and regenerated from other elements such as oxygen and nitrogen

Nucleic acids offer variability because they contain alternate forms of genes called .