Aerobic and anaerobic respiration

If you run fast, you'll get out of breath. Perhaps you have also felt a burning sensation in your muscles, when you run, or lift something heavy? That's because your body needs more oxygen than it's getting. This is how it works: Oxygen from your lungs is taken up by the blood, and brought to your muscle cells. Inside each cell, the oxygen is combined with glucose that comes from food your body has digested.

The oxygen and the glucose react, releasing energy that the body can use... and we get residues: Carbon dioxide, and water. All of this takes place inside the mitochondria of the cells. It's a pretty complex process, that takes place in several steps. The whole process is called respiration, or cellular respiration.

Cellular respiration is something different from what we mean when we talk about breathing. As a matter of fact, respiration can even take place entirely without the presence of oxygen. Respiration is a collective term for a range of processes in a cell, that release energy from nutrients, leaving waste products behind. When you run to the bus, or carry a really heavy bag, or something else that requires so much effort that you can't do it for very long… ... then your cells don't get enough oxygen, and that affects the cellular respiration.

Regular cellular respiration - that uses oxygen - is called aerobic respiration. If we remove the oxygen, it's called an-aerobic respiration. Anaerobic respiration is a simpler process, with fewer steps. It doesn't take place inside the mitochondria in the cells, but out in the cytoplasm. In anaerobic respiration, the glucose is converted without the help of oxygen, and then it doesn't release the same amount of energy.

The waste products differ too. In your muscles - when you run - the residue is lactic acid. You can feel the lactic acid as a burning sensation in your muscles, and you'll notice that there's less strength in them. When you stop the exercise, you'll keep breathing heavily for a little while. That's your body, needing some extra oxygen to process all that lactic acid that was formed in your muscles.

If you work out you've probably noticed that it takes much more effort to work anaerobically, than aerobically. It's harder to keep running, jumping, throwing, and lifting when lactic acid is present. But if you want to be faster or stronger, there are no shortcuts. Some part of your workout must be so tough that your muscles develop lactic acid. But this doesn't mean that aerobic exercise is pointless -- on the contrary.

Your body needs exercise without lactic acid too. Aerobic exercise increases the body's ability to take up oxygen, and reduces the risk of, among other things: cardiovascular diseases, cancer, osteoporosis, diabetes, depression, and Alzheimer's disease. Both in humans, and in the rest of nature, aerobic respiration is by far the most common. But there are organisms that only make use of anaerobic respiration. They are mostly bacteria, and a few multicellular organisms, living in low-oxygen environments, such as deep down in the ocean.

Common yeast, that we use when baking bread or brewing beer, is using anaerobic respiration. When bread is rising, the yeast cells don't need any oxygen at all, in order to release energy. In addition to energy, the process leaves waste products behind: Ethanol, which is a kind of alcohol, and carbon dioxide, which is what makes the bread rise. When cells metabolise nutrients, we call it respiration, or cellular respiration. There are two types of cellular respiration, with and without oxygen.

We call them aerobic and anaerobic respiration. Aerobic respiration is the most common. Aerobic respiration gives the residual products carbon dioxide and water. Aerobic respiration metabolises all the glucose, while anaerobic only metabolises some of it. That's why anaerobic respiration releases less energy, and leaves organic waste products behind.

Aerobic respiration takes place in the mitochondria of the cell. Anaerobic respiration takes place out in the cytoplasm. So, your cells can do something you can't -- they can respire without oxygen.