There is no context so I will just explain what a constant is:
In an experiment following the scientific method, a constant is a variable that cannot be changed or is purposely not changed during the experiment.
An example would be:
If a researcher wanted to study the effects of temperature on the growth and development of garden snakes, the experimental variable for the experiment would be temperature. All other variables would need to remain consistent to avoid invalid data. The size of the cage, amount of light, food and many other variables would need to remain constant to ensure accurate results and a valid study. Those variables are constants. Some variables are not under a scientist's control, but are still considered to be constants. These constants are called universal constants and include gravity, the speed of light and electronic charge. Universal constants do affect experiments but will be constant through an experiment without being controlled by the scientist.
Useable energy
this is because the whole process is transferring energy and matter for a purpose. here the purpose is useable energy. ADP, water and phosphate groups are all part of the process of generating the useable energy
The fuel used in nuclear reactors is commonly uranium. Its unstable nature means that when it is hit with an electron it splits into two new atoms, one of which is Krypton. In the process of splitting large amounts of energy is released. This energy is used to heat water to produce steam, the steams rising energy is used to turn a turbine which produces the electric output of nuclear power stations.
