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Cells require energy to perform work. Energy is obtained from extracellular sources. The process of photosynthesis by producers such as algae and green plants can convert light energy into chemical energy in the form of organic compounds such as glucose. Glucose is essentially stored or potential energy that can...

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Cells require energy to perform work. Energy is obtained from extracellular sources. The process of photosynthesis by producers such as algae and green plants can convert light energy into chemical energy in the form of organic compounds such as glucose. Glucose is essentially stored or potential energy that can be utilized by living cells during cellular respiration.

The process of respiration results in ATP which can be regenerated from ADP. The ATP molecules are then used by cells to perform work like growth, synthesis and other metabolic activities. During aerobic respiration, three stages occur including glycolysis, the citric acid cycle and oxidative phosphorylation. The cell can generate 32-34 molecules of ATP. If an organism carries out anaerobic respiration or fermentation, they carry out glycolysis and generate only 2 ATP molecules.

Organic molecules contain potential energy that is released via a catabolic pathway. Enzymes are necessary to facilitate these reactions and eventually, the energy stored in organic compounds is released as these compounds are broken down into simpler waste products containing less energy. In essence, during aerobic respiration, glucose is used as a fuel and in the presence of oxygen, it is broken down to form carbon dioxide, water, plus energy in the form of heat and ATP. The change in free energy is -686 kcal/mole of glucose and it is an exergonic reaction. The 32-34 ATP that are formed can be used for cellular work. 

In anaerobic respiration, glucose is only partially degraded and only some of its potential energy is converted to 2 ATP in the absence of oxygen. In alcohol fermentation which is carried out by yeast, glucose is converted to ethanol and carbon dioxide plus 2 ATP. In lactic acid fermentation, carried out by some fungi and bacteria, glucose is converted to lactic acid plus 2 ATP.

To summarize, in order for living things to obtain energy to stay alive, organic molecules must come from an outside source. Through the process of cellular respiration, cells will be able to regenerate ATP to be used as the energy currency for life processes.

 

 

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Cells obtain energy through the process of cellular respiration. This process can take place both aerobically as well as anaerobically. In aerobic respiration, the food (in the form of glucose molecules) reacts with oxygen and produces carbon dioxide and water molecules, along with ATP (or adenosine triphosphate) molecules. The balanced chemical equation for this reaction can be written as:

`C_6H_12O_6 + 6O_2 -> 6CO_2 + 6H_2O + ATP`

These ATP molecules are the energy currency. Energy is released (on the order of 30.6 kJ/mol) when one of the phosphate bonds is broken and ATP converts to ADP molecule. 

One can think of ATP molecules as rechargeable batteries. When cells need energy they can convert stored ATP to ADP. And when food is oxidized, ADP converts back to ATP.

Anaerobic breakdown of food is much less efficient as compared to aerobic respiration and generates very few ATP molecules.

Hope this helps. 

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The process that produces energy for the body to use is called cellular respiration.

ATP the energy source used by cells. ATP stands for adenosine triphosphate. ATP is produced during cellular respiration.  

Cellular respiration can occur in the presence or absence of oxygen. However, much more energy is produced for the body when cellular respiration is completed in the presence of oxygen. In the presence of oxygen, 34-38 ATP are produced. In the absence of oxygen, the net yield of ATP produced is 2.

ATP is formed in the presence of oxygen during the process that is known as aerobic cellular respiration. This process occurs within mitochondria of eukaryotic cells. There are three main parts of aerobic cellular respiration- glycolysis, Krebs Cycle, and the electron transport chain. Overall, aerobic cellular respiration converts the sugar called glucose and oxygen gas into carbon dioxide gas, water, and 34-36 ATP.

Here, the processes that occur during each phase of aerobic cellular respiration can be read in greater detail.

Anaerobic respiration is sometimes referred to as fermentation. Fermentation is a metabolic process in which organisms convert carbohydrates, such as starch or sugar, into lactic acid or alcohol.

Ethanol fermentation is the type of fermentation that produces alcohol. It is done by yeast and some strains of bacteria. During ethanol fermentation, pyruvate from glucose metabolism is broken into ethanol and carbon dioxide.  Because ethanol fermentation produces alcohol, it is used to produce beer and wine. The carbon dioxide produced by ethanol fermentation is advantageous in the making of breads.

During lactic acid fermentation, six-carbon carbohydrates, such as the pyruvate molecules from glycolysis or lactose, are converted into cellular energy (ATP) and lactic acid. Lactic acid occurs within muscle cells during intense intervals of activity when energy is needed at a faster rate than oxygen can be supplied. The lactic acid produced is the “burn” that athletes feel after an intense workout.

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