• Golgi complex 
• endoplasmic reticulum (ER) 

For more review on cell structure and organelles, please try the cell activity. 

Although not as directly related to the plasma membrane, the mitochondria diagrammed below are membranous organelles. Thus, their membranes consist of bobbing protein molecules in a sea of phospholipid molecules. 

Actually, the mitochondrion includes an outer membrane an inner membrane. Since each membrane includes a double layer of phospholipids, how many phospholipid layers are penetrated by arrow A?  

Click on the mitochondria in the diagram of the cell: 

The inner membrane of the mitochondrion is folded inward to form shelves called cristae. 

Food energy and oxygen are used to make ATP (adenosine triphosphate). ATP is an energy molecule which can power cell growth and provide the energy for muscle and nerve function. The food-to-ATP energy conversion occurs in and around folds of the inner mitochondrial membrane called cristae. 

Because of the important food-to-ATP energy conversions associated with its cristae, the title "powerhouse of the cell" is given to the mitochondrion. 

The cellular process of releasing energy stored in organic compounds is called cell respiration. 

The process of cell respiration consists of three steps: glycolysis, Krebs Cycle, and the cytochrome electron tranport system.. Glycolysis takes place in the cytoplasm, but the Krebs  Cycle and the cytochrome system  occur in the  mitochondrion. This is shown in the diagram below. 

 

The following chemical formula is a simplified illustration of cell respiration: 

The purpose of cell respiration is to make energy stored in the food molecule (glucose, for instance) available to the cell, since the stored energy cannot be used directly by the cell. The food molecule, therefore, must be processed to yield ATP, because the energy stored in ATP can be used by the cell. 

In the process of cell respiration, how many molecules of ATP are formed when one molecule of glucose is used? 

What role do respiratory enzymes play in the process of cell respiration? 

a. they speed up cell respiration 

b. they slow down cell respiration 

In cell respiration, the energy stored in glucose (or other organic compounds) is used to convert -(P) into ~(P) which combines with ADP to become ATP. In photosynthesis, energy from the sun is used to convert -(P) into ~(P), which combines with ADP to become ATP. 

The diagram illustrates the process of cell respiration using a carbohydrate as an energy source. There are three major steps -- glycolysis, the Krebs citric acid cycle and the hydrogen transport system -- all of which take place only in the presence of respiratory enzymes. 

In glycolysis, one molecule of glucose releases the energy required to change two molecules of ADP to two molecules of ATP. Two molecules of pyruvic acid and four hydrogen atoms are given off. 

Glycolysis occurs in the cytoplasm, outside the mitochondrion. 

The acetyl CoA (coenzyme A) molecules enter the second major step of cell respiration. 

What is this step called? 

Kreb Cycle 

Where does this step occur in the cell? 

(in the fluid matrix) 

Up to this point in cell respiration, how many carbon dioxide molecules and hydrogen atoms have been liberated? 

CO2 

H 

The 24 hydrogen atoms that have been liberated enter the third major step of cell respiration. This step is called the hydrogen transport system (or the electron transport system), and it occurs in the cristae of the mitochondrion. 

How many molecules of ATP are released, when one molecule of glucose is completely used in the process of cell respiration? 

Which step of cell respiration yields energy most efficiently? 

In which major step of cell respiration is oxygen used? 

What does the oxygen combine with to form water? 

This is the end of  lesson eight . Click here to go back to the home page and lesson nine:  Photosynthesis- Overview Part I.    click 

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Last modified October 29, 1997.