Cells get energy from a process called cell respiration. When you eat something, most of the nutrients will go through cell respiration, and will be converted into energy. Inside the cell, the Mitochondria, the "powerhouse of the cell" is converting all of the nutrients into Adenosine triphosphate or ATP. This ATP energy. Without ATP you wouldn't be able to do many things like sports.
Photosynthesis is another process a plant cell uses to get sugar. It converts light energy or the sun into chemical energy. A product it produces is oxygen. The plant then burns the sugar the same way we burn sugar. Through the Mitochondria.
Cities usually get energy from power plants, such as coal and wood power plants. These power plants do make a lot of energy, but they pollute the air while doing so, making many people sick. Some cities use more environmental friendly power plants such as wind and solar power plants. However these power plants also have faults, solar power doesn't work in cold areas and wind power doesn't work as well in places with low winds. Cities get the energy by burning coal/wood then having the fire heat water which causes steam, the steam then powers the generator which creates electricity. And that's just for coal/wood power plants!
It is clear that cells get energy more efficiently. According to sources on the internet, cell respiration is about 40% efficiency whereas power plants are at about 34% efficiency. This shows that cells are slightly more efficient. They are only slightly more efficient because both sources of energy produce CO2 as a waste product when they burn nutrients. This means that cells and power plants produce the same waste products. Its just that cells are more efficient in terms of useful energy VS waste heat.
Some Information found at http://www.conserve-energy-future.com/AlternativeEnergySources.php,
http://www.explainthatstuff.com/powerplants.html