Why do aerobic cells need oxygen

Eukaryotes can also undergo anaerobic respiration. Some examples include alcohol fermentation in yeast and lactic acid fermentation in mammals.

The fermentation method used by animals and certain bacteria like those in yogurt is called lactic acid fermentation. This type of fermentation is used routinely in mammalian red blood cells and in skeletal muscle that has an insufficient oxygen supply to allow aerobic respiration to continue that is, in muscles used to the point of fatigue. The excess amount of lactate in those muscles is what causes the burning sensation in your legs while running.

This pain is a signal to rest the overworked muscles so they can recover. In these muscles, lactic acid accumulation must be removed by the blood circulation and the lactate brought to the liver for further metabolism. The chemical reactions of lactic acid fermentation are the following:. Lactic acid fermentation : Lactic acid fermentation is common in muscle cells that have run out of oxygen.

The enzyme used in this reaction is lactate dehydrogenase LDH. The reaction can proceed in either direction, but the reaction from left to right is inhibited by acidic conditions. Such lactic acid accumulation was once believed to cause muscle stiffness, fatigue, and soreness, although more recent research disputes this hypothesis.

Once the lactic acid has been removed from the muscle and circulated to the liver, it can be reconverted into pyruvic acid and further catabolized for energy.

Another familiar fermentation process is alcohol fermentation, which produces ethanol, an alcohol. The use of alcohol fermentation can be traced back in history for thousands of years.

The chemical reactions of alcoholic fermentation are the following Note: CO 2 does not participate in the second reaction :. Alcohol Fermentation : Fermentation of grape juice into wine produces CO2 as a byproduct. Fermentation tanks have valves so that the pressure inside the tanks created by the carbon dioxide produced can be released. The first reaction is catalyzed by pyruvate decarboxylase, a cytoplasmic enzyme, with a coenzyme of thiamine pyrophosphate TPP, derived from vitamin B 1 and also called thiamine.

A carboxyl group is removed from pyruvic acid, releasing carbon dioxide as a gas. This releases only enough energy to make two ATP molecules. With oxygen, organisms can break down glucose all the way to carbon dioxide. This releases enough energy to produce up to 38 ATP molecules. Thus, aerobic respiration releases much more energy than anaerobic respiration.

The amount of energy produced by aerobic respiration may explain why aerobic organisms came to dominate life on Earth. It may also explain how organisms were able to become multicellular and increase in size. One advantage of anaerobic respiration is obvious. It lets organisms live in places where there is little or no oxygen. Such places include deep water , soil, and the digestive tracts of animals such as humans see Figure below.

Another advantage of anaerobic respiration is its speed. It produces ATP very quickly. For example, it lets your muscles get the energy they need for short bursts of intense activity see Figure below. Some of these antioxidants are enzymes and others are not.

Plant cells have high levels of antioxidants, since photosynthesis generates toxic forms of oxygen. You acquire some of these antioxidants when you eat plant cells. In some cases, they act as antioxidants in your cells too. Vitamin C, Vitamin E, and the precursor to Vitamin A are all antioxidant compounds that you need in your diet. Vitamin C is mostly needed to maintain connective tissues while Vitamin A is mostly needed by the light-sensitive cells in the back of your eye.

Both Vitamin A and C may also act as antioxidants in your cells, however. Vitamin E is an effective antioxidant in your cells and those of plants. You can gain whatever antioxidant benefits these compounds provide by including plenty of fresh fruits and vegetables in your diet. You can also get them from supplements vitamin pills but take care.

Both Vitamin A and E are toxic at high dosages. Now that you understand how cells get energy from the sun photosynthesis by green plant cells or from food non-photosynthetic cells, including yours , let's discuss energy flow through a multi-celled organism, which is an assemblage of many cells working together.

Let's use your body as an example. In a multi-celled organism, cells are organized into tissues. Tissue are combined into organs and organs cooperate in "organ systems". One of these is the digestive system of your body. The digestive system includes the digestive tract, a pathway through your body that is taken by the food you eat.

The digestive tract includes mouth, esophagus, stomach, and intestines small and large. The liver and pancreas are part of the digestive system also. The liver stores blood sugar glucose as glycogen animal starch and produces bile salts for the digestion of fats in the small intestine. The pancreas secretes digestive enzymes and bicarbonate buffer to neutralize stomach acid into the small intestine. The pancreas also releases insulin and glucagon into the blood. These are two hormones that act to maintain a stable concentration of glucose in the blood.