 You are running a 1500 meter race, breathing deeply to get the oxygen so that you can respire and keep up the energy supplied to your muscles. Your muscles keep wanting more and more energy, but your lungs can't keep up. Do you have to quit the race? No. In the respiration video, we discovered the difference between aerobic and anaerobic respiration and then looked at aerobic respiration in more detail. Sometimes animals and plants can't get enough oxygen to respire aerobically, such as during intense exercise, but they still need to respire to survive. After all, everything relies on respiration for energy. Luckily, there is a backup plan, anaerobic respiration. In this video, we are going to have a look at anaerobic respiration in both animals and plants. Starting with animals, a cheetah sprinting to catch some prey cannot take enough air and blood around the body fast enough for aerobic respiration. The heart and lungs can't keep up, so anaerobic respiration is carried out instead. Here is the generalized equation for anaerobic respiration. See how it differs from aerobic respiration. There is no oxygen involved in anaerobic respiration. It is much less efficient than aerobic respiration and much less energy is released. This is because the glucose is only partially broken down. Another problem is that lactic acid is produced. This is actually a poisonous chemical that if it builds up in the body, the muscle stops working and you get a muscle cramp. You can only get rid of lactic acid by taking in oxygen again and thus replacing the oxygen there. Oxygen is needed to break down lactic acid, turning it into carbon oxide and water. You know how you breathe deeply after intense exercise? This is your body replacing the bulk of oxygen there. So that is how anaerobic respiration works in animals. What about in plants? The oxygen supply can run out for plants too, such as in waterlogged soils. This then forces plants to have to carry out anaerobic respiration, as they too need to respire constantly. Here is the generalized anaerobic respiration equation for plants. Notice how instead of lactic acid being produced, ethanol and carbon dioxide is made instead. In yeast, this process is called fermentation and it is used to bake bread and brew alcohol. Ethanol is the alcohol found in beer and wine for example. And in bread making, it is the carbon dioxide that is useful. The bubbles in carbon dioxide help the bread rise by expanding the dough. So you should now know that when our heart and lungs cannot keep up with the oxygen demand, or plants do not have access to sufficient oxygen, we have a B-plan, anaerobic respiration. This is when the glucose is broken down directly, but it produces much less energy than aerobic respiration, which is why it is the second choice. And in animals it produces lactic acid as a by-product which causes muscle cramps. And so we end up with an oxygen dead which needs repain of the exercise I stopped.