Before we start there are some terms you need to know
NAD+ is an empty electron carrier, when charged it become NADH
FAD+ is an empty electron carrier, when charged it become FADH
ADP is Adenosine Di Phosphate, when charged it become ATP (Adenosine Tri Phosphate). ATP is the bodies main energy molecule in cells.
Respiration is how cells generate energy. There are two forms of respiration:
Anaerobic respiration/Glycolysis
Cellular respiration/ aerobic respiration
First stage of all respiration
Anaerobic respiration or glycolysis occurs in the cytoplasm of the cell. As the name suggests it does not require any oxygen. At this stage we split glucose into two smaller molecules, called pyruvate. In this process we get a net profit of two ATP molecules and two NADH molecules.
If there is no oxygen is present, pyruvate passes into fermentation. If there is oxygen present than they will enter the mitochondria and being aerobic respiration.
The inputs and outputs are:
Fermentation
Fermentation is the next stage if oxygen is NOT present.
As you can see by the animation to the left,animals, plants, yeast and bacteria form different products when there is no oxygen present.
Animals will form Lactic Acid, where as the others will form Carbon dioxide and ethanol.
Aerobic respiration
This is where cellular respiration really starts. When oxygen is present in the cells, pyruvate molecules enter the mitochondria starting a long sequence of reactions, resulting in 34-36 ATP molecules. Although this may sound like a lot, compared to the 2 formed by glycolysis, cellular respiration is actually quite an inefficient process. In fact 60% of the energy stored in glucose is lost as heat during these reactions.
In cellular respiration there are two main processes which occur in the mitochondria. The kerbs cycle and the Electron transport chain.
As we follow pyruvate into the matrix of the mitochondria, a small Co-enzyme called CoA attaches its self to the pyruvate molecule, changing the pyruvate into Acetyl Co-A. As the molecule is altered the extra energy released is captured by an NAD+ molecule, turning it into NADH.
This is referred to as the Prep-Step
Kerb cycle
The next step in cellular respiration is the Kerb cycle. Now this is where it begins to get complicated.
For now all you need to know is this process occurs in the Matrix of the mitochondria.
2 Acetyl Co-A molecules are used to generate 6 NADH molecules, 2 FADH, 2 ATP and 4 CO2 molecules. This is illistrated in the diagram to the left
The NADH and FADH molecules pass over to the electron transport chain. At the end of this stage we have a total of 10 NADH and 2 FADH molecules.
At this stage no oxygen has been used
Electron transport chain
This is the final step in cellular respiration. This is where the most ATP is created through out the whole process.
Glycoloysis and the kerb cycle have been leading up to this moment. At this stage we use the 10 NADH molecules and the 2 FADH molecules to created 32 ATP molecules. This process occurs in the membrane folds of the mitochondria (Cristae).
In prokaryotes this will occur on the surface of the cell membrane.
At the end there are 36 ATP molecules produced overall, with the help of oxygen.
Water is also produced at this stage
The entire process of cellular respiration is shown in the animation bellow. This is a simplified version of cellular respiration
Once you have read the information above give a shot at the quiz bellow.
During intense exercises (such as sprinting) a large amount of lactic acid is formed (anaerobic respiration).
Lactic acid is very high in energy, so it would be a waste to dispose of it. For this reason lactic acid is stored in the liver until oxygen is present again.
Once we have oxygen, most of the lactic acid is converted back into glucose and used in aerobic respiration. The amount of oxygen required to recycle the lactic acid is the Oxygen debt.
Its important to know that although carbohydrates are the main source of energy in cellular respiration, fats and proteins can be used too.
Fats give off more energy per gram than either carbohydrates or proteins.
The graph bellow shows how each energy system is used over time.
