Types: 1 Mark each
Cells need a source of energy. They get this energy by breaking down glucose obtained from the food. This process is called 'cellular respiration'. 
There are 2 types of cellular respiration - 
During aerobic respiration, glucose is broken down into carbon dioxide and water in the presence of oxygen to release energy. 
During anaerobic respiration, glucose is broken down into alcohol and carbon dioxide in the absence of oxygen to release a little bit of energy.