Growth I think could be right
If there a too many producers but not enough secondary consumers, the ecosystem becomes unbalanced and the energy is unused. So the number needs to balanced for the ecosystem to be as well.
2. to keep the body's internal environment in balance
I think that these factors are :the type of radiation , the duration of exposure to the radiation and the amount of radiation exposure. Radiation is commonly used to treat many medical conditions. Frequently used as a therapy for various forms of cancer, it is common for radiation to cause death of cells both cancerous and healthy cells in the areas irradiated. The extent of damage caused depends on the type of radiation irradiated, the duration of exposure and the amount of radiation.
The earth orbits the sun once per year