Describe the principles of fission and fusion. With reference to the nuclear binding energy curve, explain how energy is released.

Fission is the process by which heavier unstable elements split into smaller fragments, and releases energy for elements further to the right on the BE curve than iron. The fission fragments are further to the left on the BE curve than the original nucleus and have higher BE per nucleon. This causes a mass defect and in turn energy to be released.
Fusion occurs when two lighter nuclei fuse into a heavier one. They once again move up the BE curve but this time begin from the left of the curve (if the reaction is to release energy). Similarly to fusion the higher binding energy of the new nucleus causes a release of energy.