What makes the cell membrane selectively permeable?

What is the main fuel source for the work of the cell

Why do some dna fragments move farther than others during gel electrophoresis? a. because their shapes are different b. because they are different types of molecules c. because the samples are different colors d. because their masses are different

Which rate indicates the number of children that would be born per women if she were to live to the end of her child-bearing years