Which organelle forms the surface of a cell, separating its contents from the outside world

What is mitosis and how does it affect change

What was the land like over 500 million years ago? what was under the sea?

Students in biology are studying the macromolecules of life. they used a calorimeter to determine the calories in various types of food. once the lab was completed, the students ate the left over food samples. monica commented that in just 6 or 7 "chews" of the saltine, it was gone; nothing but a sticky paste in her mouth. elaborate on what happened chemically while chewing the saltine. include the macromolecules present.