 Now, we'll take a closer look at the three stages of cellular respiration. While we've noted that each of the three stages does give off some ATP, the maximum efficiency is reached when all of the stages are operating simultaneously. 10 points if you've noticed I draw an animal cell, and we're wondering why, because animals and plants all do respiration, I just thought it was easier to draw. Okay, let's have a look at glycolysis. Glycolyco means sugars, lysis means breakdown, or splitting. So glycolysis is a stage where the sugars are broken down. If we're working with our model glucose, it's a six-carbon molecule, and it's broken down into two three-carbon sugars called pyruvates. The process of glycolysis takes 10 steps done by 10 different enzymes who each have a specific job to do. To start glycolysis, the cell actually does need some energy in the form of ATP, and so it draws on some ATP that it has stored. Another important part of respiration is electron transfers. Generally, this is done using an ion, NAD+, which stands for nicotinamide adenine dinucleotide. What happens here is that the cell takes some NAD+, that's got lying around, and adds an electron, which converts it to NADH, and another H+, which is a hydrogen ion, also known as a proton. This is a way that the cell holds on to electrons for use later in the electron transport chain. What's great about glycolysis is that it does not need oxygen. This first step, where we break glucose down into smaller sugars, is done anaerobically without oxygen. Using the steps of glycolysis, some water is also produced. So, to summarise glycolysis, for every one molecule of glucose, two molecules of ATP are produced, two sets of NADH and two protons, and two pyruvate molecules are produced.