Respiration and burning fuels
Fossil fuel+oxygen>carbon dioxide+water+energy
NOTE: Amount of ATP produced in aerobic respiration may vary
Glucose is all we need for anaerobic respiration, we get glucose from the food we eat. Anaerobic respiration is the first part of aerobic respiration but in order to carry out aerobic respiration we also need oxygen, we get oxygen for the air by breathing. Glucose and oxygen are transported to respiring cells in the blood. Anaerobic respiration takes place in the cytoplasm of the cell and aerobic respiration takes place in the mitochondria.
Why we need oxygen
Aerobic respiration can only take place in the presents of oxygen. Anaerobic respiration only produces 2 ATP per glucose molecule which isn't enough to carry out continuous activity, during continuous activity heat is produced in the muscles and lactic acid will be produced due to a lack of oxygen, more lactic acid and a higher temperature will encourage the release of oxygen from oxyhaemoglobin increasing the oxygen debt.
Oxygen is needed to convert lactic acid into a 3-carbon compound, when there is not enough oxygen to convert all the lactic acid the lactic acid is stored in the liver, the oxygen debt is the amount of oxygen needed to convert all this stored lactic acid into the harmless 3-carbon compound.