The definition of energy is the ability to do work, and it takes work to maintain the organism. (Mader and Windelspecht et al., 2010, p.4) The principle of conservation of energy is that the total amount of energy in a closed system always remains the same, none is lost or created in any chemical or physical process or in the conversion of one type of energy into another, within that system. (Biology Online, 2005) The sun is the main source of energy in the biosphere, solar energy can be converted into many different forms of energy, such as chemical energy, kinetic energy, electrical energy, thermal and so on. The energy transfer approach is called energy flow, which can make the total energy in the biosphere maintain balance. The purpose of this essay is to describe the transfer and flow of energy in the ecosystem and explain how they benefit humans. In the main body of this essay, divided into three parts, from the ways of photosynthesis, cellular respiration and electrical generation, to describe the transfer and flow of energy and explain why it is vital to human existence ahead. Plants and some other organisms are capable of capturing solar energy and carrying out photosynthesis, a process that transforms solar energy into the chemical energy of organic nutrient molecules. (Mader and Windelspecht et al., 2010, p.4) When leaf cells perform photosynthesis, they use solar energy to form carbohydrate molecules from carbon dioxide and water. Carbohydrates have many long chemical chains and they bind together so that they can store energy as much as possible. Not all captured solar energy becomes carbohydrates; some of them become heat. (Mader and Windelspecht et al., 2010, p.105) No part of the energy in the plant is destroyed, part of the energy is stored in carbohydrates... middle of paper... protection, renewable energy sources are becoming more and more popular among Western countries. Renewable energy, such as solar energy, wind energy, hydropower, are recyclable and can replace nuclear energy and fossil fuels to transfer energy to meet electricity needs. Electricity can bring convenience and efficiency to our daily lives. Lighting, transportation and technologies all rely on electrical generation, so energy conversion is certainly essential to modern life. In conclusion, the energy in our ecosystems can be transferred in various forms, but it cannot be transformed into the total amount of energy. Due to limitations, this essay cannot contain all energy transfer, it only describes photosynthesis, cellular respiration and electrical generation in these three ways. However, energy is vital to our existence in general.