Convection cells in the sun's convection zone carry energy from the top of the radiative zone to the photosphere. in the convection cells, hot gases rise to the photosphere, cool, and then sink back into the convection zone. what causes the transfer of energy in this process?

Hot gases.

There are three types of heat transfer or heat propagation; conduction, convection and radiation. Heat transfer is the process by which heat projects externally however, depending on the temperature and pressure. Also called the movement of heat from a low temperatured state which increases as heat progresses.
Conduction is the heat transfer by contact, immediate contact.
Convection is the transfer of heat through air and water.
Radiation is the transfer of heat regardless of the presence of atoms or particles. 

1.989×10^30 kg is the weight of the sun.

If you remove all the lions from the savanna it will lead to a increase of gazelle and a increase of cheetahs becasue of no competition