Ecology

Lesson 2.3

2.3.7 Cellular Respiration Key Information, Ed Portal

1. Formula - Memorize and be able to explain this key formula. Know the chemical names, numbers, and symbols. It is similar to photosynthesis, except backwards and there is no light required. The reactants and products are switched because energy is being released and not stored.

1. C6H12O6 + 6O2  6CO2 + 6H2O
2. In words, the formula reads, “One molecule of glucose and six molecules of oxygen yields/produces six molecules of carbon dioxide and six molecules of water.”

2. Movement of Molecules - Glucose enters the cell through the blood, digestion of larger molecules, or is being produced by plants during photosynthesis. Glucose is broken down during glycolysis to form two 3 carbon molecules called pyruvate. Pyruvate moves into the matrix of the mitochondria. The link reaction then occurs, followed by the Krebs or Citric Acid cycle. CO2 is produced during the link reaction and Krebs/Citric Acid cycle and is breathed out by cells. NADH and FADH2 molecules produced during the link reaction and Krebs/Citric Acid cycle move to the inner membrane where they drop off electrons and energy to start the electron transport chain and chemiosmosis. Water is the final electron acceptor and is produced at the end of the electron transport chain. Water is produced when oxygen, that has been breathed into the cell, combines with electrons and hydrogen atoms. Water then leaves the cell as waste or is used for other cellular functions.
3. Rearrangement of Carbon Molecules - The carbon molecule of glucose rearranges through a series of metabolic reactions in the cell to form carbon dioxide. The first process is glycolysis, which splits the 6 carbon molecule into two 3 carbon molecules called pyruvate. Pyruvate is then change into acetyl coenzyme A, a 2 carbon molecule. This allows acetyl coenzyme A to enter the Krebs/Citric Acid cycle, where there are 8 different steps. CO2 is produced in two places during these 8 steps. If you take Biology or Biochemistry in college, you will learn all the different steps, enzymes, and intermediates, but it is not required for high school.

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Figure 2.3.5

4. Energy Flow - Chemical energy stored in the high-energy carbon-carbon and carbon-hydrogen bonds of glucose is converted into chemical bonds in adenosine triphosphate (ATP). The energy stays in the same form - chemical energy. The process is long and complex, but the result is energy that the cell can easily and readily use. ATP is the cellular unit of energy because cells can use it quickly and easily. The chemical energy in ATP is stored in a phosphate-phosphate bond between the second and third phosphate groups of ATP. The useful thing is that when ATP gives energy to the cell, the waste products of adenosine diphosphate (ADP) and a free phosphate group can be recycled and used over and over again.
5. Differences between aerobic and anaerobic respiration - There is a short answer for the difference between aerobic and anaerobic respiration. Aerobic requires oxygen! Anaerobic (the an- prefix means “not”) does works without oxygen. Second, time is a factor. Aerobic respiration takes about 30 minutes but anaerobic is nearly instantaneous. If cells need a quick boost of ATP energy, anaerobic is the best way to go. A third difference is the amount of ATP produced. Aerobic produces 36 ATP per glucose molecule and anaerobic only produces 2 ATP per glucose. If cells need to maximize ATP production, they do aerobic respiration. There are two main types of anaerobic respiration - lactic acid fermentation and alcoholic fermentation. You can feel the lactic acid build up in your muscles if you run up the stairs quickly. Here is a college-level comparison of aerobic and anaerobic respiration.