Glucose-------> aerobic respiration ------ CO2 + water
           ---------> anaerobic respiration ------ alcohol +water
           ---------> respiration without oxygen(in muscles) ------- lactose + water
1 5 1
The process of aquiring oxygen from outside the body, and use it in the process of break-down of food sources for cellular needs, is what we call respiration
Oxidising-reducing reactions are some of the mosst common chemical means to break-down molecules..
1. Glycolysis: 
a ten-step process that occurs in the cytoplasm 
converts each molecule of glucose to two molecules of pyruvic acid (a 3-carbon molecule) 
an anaerobic process - proceeds whether or not O2 is present ; O2 is not required 
net yield of 2 ATP per glucose molecule 
net yield of 2 NADH per glucose (NADH is nicotine adenine dinucleotide, a co-enzyme that serves as a carrier for H+ ions liberated as glucose is oxidized.) 

The pyruvic acid diffuses into the inner compartment of the mitochondrion where a transition reaction occurs that serves to prepare pyruvic acid for entry into the next stage of respiration: 
(a) pyruvic acid ® acetic acid + CO2 (a waste product of cell metabolism) + NADH+ 
(b) acetic acid + co-enzyme A --> acetyl CoA 

2. Citric Acid or TCA Cycle: 
occurs in the inner mitochondrial matrix 
the acetyl group detaches from the co-enzyme A and enters the reaction cycle 
an aerobic process; will proceed only in the presence of O2 
net yield of 2 ATP per glucose molecule (per 2 acetyl CoA) 
net yield of 6 NADH and 2 FADH2 (FAD serves the same purpose as NAD) 
in this stage of cellular respiration, the oxidation of glucose to CO2 is completed 

3. Electron Transport System: 
consists of a series of enzymes on the inner mitochondrial membrane 
electrons are released from NADH and from FADH2 and as they are passed along the series of enzymes, they give up energy which is used to fuel a process called chemiosmosis by which H+ ions are actively transported across the inner mitochondrial membrane into the outer mitochondrial compartment. The H+ ions then flow back through special pores in the membrane, a process that is thought to drive the process of ATP synthesis. 
net yield of 34 ATP per glucose molecule 
6 H2O are formed when the electrons unite with O2* at the end of electron transport chain. [* Note: This is the function of oxygen in living organisms!]