Cholesterol, I believe is the answer.
The juice in the can is colder than the juice in the bottle because the can is metal, and metal heats/gets cold faster than the bottle which is made of plastic. Metal can also hold the heat or cold longer than plastic can. However, it does not effect the contents of the metal can or the plastic bottle.
If it were to be one giant cell, it would be hard to transport materials across the membrane. Being multicellular allows transporting materials faster and more efficient.
Answer:
because existing cells divide to produce new cells
