Which organelle below is the "brain" or control center for a cell?
a. nucleus
b. cell wall
c. cell membrane
d. vacuole

When a spring is compressed, the energy changes from kinetic to potential. which best describes what is causing this change?

8.98 dm3 of hydrogen gas is collected at 38.8 °c. find the volume the gas will occupy at -39.9 °c if the pressure remains constant.

Large helium-filled balloons are used to lift scientific equipment to high altitudes. what is the pressure inside such a balloon if it starts out at sea level with a temperature of 10.0ºc and rises to an altitude where its volume is twenty times the original volume and its temperature is – 50.0ºc ?