Facultative anaerobic

A facultative anaerobe is a organism that can survive in the presence of oxygenyou can use oxygen in the aerobic respirationbut it can also survive without oxygen through the fermentation or the anaerobic respiration. Most of the eukaryotes are obligate aerobes and cannot survive without oxygen. Prokaryotes tolerate a wide range of oxygen, from obligate anaerobes which are poisoned by oxygen, to facultative anaerobes and obligate aerobes. Some prokaryotes are even aerotolerantmeaning that they can survive in oxygen, but use anaerobic pathways for energy.

A facultative anaerobe can experience the best of both worlds. In times of low oxygen, a facultative anaerobe can use fermentation or anaerobic respiration to create ATP for the cells, usually still from the breakdown of glucose. The only real difference between these pathways and aerobic respiration is that they utilise a receptor electron acceptor at the end of the pathway. Aerobic respiration depends on oxygen to accept electrons at the end of the pathway. electron transport chain. A facultative anaerobe can use a variety of other pathways to deal with these additional electrons, as explained in the examples.

It should be noted that facultative anaerobes are sometimes called facultative aerobes. The terms are generally interchangeable.

Examples of facultative anaerobes

Yeast

A common facultative anaerobe is the yeastwhich is used in various baking applications, such as making bread or beer. In any case, this facultative anaerobe must function without oxygen. However, the yeast can still survive and must do so for these products to do well.

In bread, yeast is responsible for making bubbles in the dough. These air pockets make the bread light and fluffy. Otherwise, the bread would bake into a solid dough more like a cake or brownie. Yeast creates these air pockets by releasing carbon dioxide, which makes the bread light and fluffy. carbon dioxidea by-product of converting the glucose in the dough into energy. To obtain a lighter, more airy dough, chefs often let the dough “rise”. This term simply means placing the yeast-laden dough in a warm place and allowing the facultative anaerobe to do its work. Over the course of about an hour, the yeast will create large amounts of carbon dioxide within the dough, expanding it and making it lighter.

In beer, wine and other alcoholic beverages, yeast is the key ingredient. The process of fermentation, or the creation of alcohol, occurs in yeasts when they have a lot of sugar but little oxygen. Brewers and winemakers use this aspect of the facultative anaerobe to generate the alcohol within their products. Aerobic respiration reduces glucose completely to a few recyclable molecules and carbon dioxide. Fermentation, on the other hand, leaves an end product: ethanol. Brewers and wine makers create ethanol (an alcohol) in their products by strictly controlling the amount of sugar and oxygen in their fermentation tanks. Under these conditions, any facultative anaerobe will resort to fermentation and discard ethanol as a by-product. When the alcohol reaches the right level in the mixture, the yeast is filtered out and the beverage is bottled.

Molluscs

While most think only of small unicellular facultative anaerobes, several larger groups of animals have evolved the ability to survive without oxygen. One of these, the molluscs, has a group of organisms that have adapted to survive regular periods without oxygen. Mussels, which are often found in areas where they intertidalThe mussels experience daily changes in their access to the water. When the tide goes out, mussels are exposed to the air and must close their shells to prevent them from drying out. In some areas, the tide may fall for significant periods of time. Mussels cannot open their shells to obtain oxygen, or they risk drying out and dying from dehydration.

To solve their riddle, mussels like those pictured above have evolved the abilities of a facultative anaerobe. Instead of relying on their normal aerobic respiration when the tide goes out, the mussels switch to a form of energy that decomposes the amino acids. This allows the mussel to survive for hours, or even days, without obtaining a new source of oxygen.