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Cellular Respiration
All cells need energy to do their work. Enzymes use energy in the form of ATP to help reactions happen. Energy is used to move materials in and out of cells. A cell gets this energy from the food an organism eats. How does a cell change the energy from food into the form of ATP? Recall that the reactions a cell uses to create and use ATP are called cellular respiration.

You may have heard the word respiration. Respiration is about breathing. When you breathe air in and out, you respire. You breathe in oxygen and breathe out carbon dioxide. Cellular respiration is the process a cell uses to transform chemical potential to energy. The cell uses this energy for metabolism and growth. The equation for cellular respiration is :
C6,H12,O6 + 6-O2 ----> 6-CO2 + 6-H2O + 36-ATP

This equation shows that cellular respiration uses 02 (oxygen) and produces C02 (carbon dioxide). This is similar to human respiration. The oxygen in the air you breathe in is used in cellular respiration. The oxygen enters the lungs and is absorbed into the blood. The blood carries the oxygen to all the cells in your body. Cells use this oxygen for cellular respiration.

In addition to oxygen, cellular respiration uses glucose. Recall that glucose has the chemical formula C6H1206. Organisms use glucose as their main energy source. You get glucose from the food you eat.

Cellular respiration produces carbon dioxide. This gas is absorbed back into the blood. The blood carries the carbon dioxide back to the lungs. You breathe carbon dioxide out as a gas.

To sum up, you inhale oxygen into your lungs from the air. Your blood carries the oxygen from your lungs to the cells for use in cellular respiration. Your blood carries carbon dioxide produced from cellular respiration back to the lungs, where it is exhaled.


How a Cell Gets Energy from Glucose
How does a cell get energy from glucose? Remember that glucose is a sugar molecule. Glucose has energy stored in its bonds. When these bonds break, they release energy. The energy released is in the form of electrons. The electrons are transferred from glucose to other molecules involved in cellular respiration. The chemical reactions that transfer these electrons are called redox reactions.

The word redox is formed from two words, reduction and oxidation. Reduction refers to chemical reactions in which a molecule gains electrons. Oxidation refers to chemical reactions in which a molecule loses electrons. The two words are joined because one molecule gains electrons from another molecule losing them.

The figure that looks like an equations below shows that glucose undergoes oxidation and loses electrons during cellular respiration. Through many reactions, the electrons are transferred to the oxygen molecules. As oxygen is reduced, it bonds with hydrogen ions in the cell. The result is water, or H2 0. Water is another product of cellular respiration.

To sum up, you inhale oxygen into your lungs from the air. Your blood carries the oxygen from your lungs to the cells for use in cellular respiration. Your blood carries carbon dioxide produced from cellular respiration back to the lungs, where it is exhaled.

When hydrogen combines with oxygen to make water, the reaction is explosive. Combining hydrogen gas and oxygen gas releases a lot of energy quickly. A cell does not force these two gases together. Instead, it uses many chemical reactions to slowly release this energy in a step-by-step process. As this energy is released, the cell uses it to create ATP.

The slow release of energy happens by transferring electrons through several different molecules. Electron carriers are special molecules that help the cell with redox reactions. Specifically, cellular respiration uses an electron carrier called NAD+.

When electrons are transferred to this molecule, NAD+ reacts with hydrogen in the cell to form NADH. The many reactions involved in cellular respiration produce NADH. The amount of NADH produced helps determine how much overall ATP is produced.

Cellular respiration involves many different chemical reactions. These reactions are grouped into three stages. They are glycolysis, the Krebs cycle, and electron transport.


1. ............... is the reactions a cell uses to create and use ATP.
2. For cellular respiration, you breath in .......... and breath out .......... .
3. Write the equation for cellular respiration.
4. Cells use the ............... you breath in for cellular respiration.
5. ............... that is in the food you eat is also used in cellular respiration.
6. Cellular respiration produces ............... that is breathed out.
7. Energy is released from glucose in the form of ............... .
8. Glucose loses .......... and hydrogen during cellular respiration.
9. Oxygen bonds with ........... during cellular respiration to form H2O.
10. ............... produced produced from the glucose during cellular respiration is exhaled from the lungs.
11. The energy produced when hydrogen bonds with oxygen is used to create .......... .
12. Cellular respiration uses an electron carrier molecule called ............... .
13. NAD+ reacts with hydrogen to form NADH when is receives an electron.
14. In the 2nd and 3rd stages of Cellular respiration, NADH is use to make .......... .
15. The three stages of cellular respiration are ....
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