Prime objective of this lecture is to present on Interactions of Life. It is a tutorial study based lecture. Here briefly describe how organisms obtain energy for life, explain how organisms interact and recognize that every organism occupies a niche. Living organisms need a constant supply of energy. Some organisms use the Sun’s energy to create energy rich molecules through a process called photosynthesis. Energy is stored in the chemical bonds of the atoms. When the bond is broken, energy is released to fuel life processes.