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Release of Energy – Detailed Explanation

Grade 7
Sep 9, 2022


Release of Energy  

Food web organisms transmit energy from producers to consumers. Organisms require energy to complete complicated activities. The great majority of energy in food webs comes from the Sun and is turned (processed) into chemical energy via the photosynthesis process in plants. When molecules are broken down during respiration in plants, a tiny fraction of this chemical energy is converted directly into heat. A variety of consumers, including cows, rabbits, horses, sheep, caterpillars, and other insects that eat plants, convert the majority of the chemical energy contained in plants into other forms. 

10% energy law

Some of the chemical energy held in a producer, such as grass, is stored as chemical energy in the fat or protein of the first-order consumers that consume the grass. This energy is available to consumers of higher order. The majority of chemical energy is transferred to other forms, such as heat, at each level of a food chain and does not remain within the environment. 

Release of Energy in Cellular Respiration  

In the presence of oxygen, glucose is broken down to create carbon dioxide and water during cellular respiration. The energy-carrying molecule ATP absorbs the energy released during the reaction (adenosine triphosphate).  

Reaction of Respiration

An adenosine molecule is bound to three phosphate groups in a row to form adenosine triphosphate (ATP). Chemical energy in food is transformed into chemical energy that the cell may utilize and store in ATP molecules through a process known as cellular respiration. This happens when an adenosine diphosphate (ADP) molecule uses the energy generated during cellular respiration to bind with a third phosphate group, forming an ATP molecule.  

Formation of energy

The ATP connection between the second and third phosphate groups stores energy from cellular respiration. When a cell demands energy to accomplish work, ATP loses its third phosphate group, releasing the energy contained in the bond for use by the cell. It has now been converted back to ADP and is ready to store the energy from respiration by joining with a third phosphate group. ADP and ATP are constantly converting back and forth in this manner.  

Structure of ATP


Glycolysis is a process that extracts energy from glucose by breaking it into two three-carbon molecules known as pyruvates. Glycolysis is an old metabolic process, which means it developed a long time ago and is present in the vast majority of species alive today. The first stage of cellular respiration in species that conduct it is glycolysis. However, glycolysis does not require oxygen and is seen in many anaerobic species (organisms that do not use oxygen). Glycolysis occurs in the cytoplasm of a cell and is divided into two phases: the energy-requiring phase and the energy-releasing phase.                                              

Glycolysis – Energy-Requiring Phase  

During this step, the initial molecule of glucose is rearranged, and two phosphate groups are connected to it. The phosphate groups render the modified sugar, now known as fructose-1, 6-bisphosphate, unstable, allowing it to split in half and generate two phosphate-bearing three-carbon sugars. Because the phosphates utilized in these processes are derived from ATP, two molecules are depleted.  

Glycolysis - Energy-Requiring Phase

The three-carbon sugars generated when the unstable sugar degrades are distinct from one another. Only one, glyceraldehyde-3-phosphate, may proceed to the next stage. However, because the unfavorable sugar, DHAP, is quickly transformed into the favorable sugar, both complete the pathway in the end.  

Glycolysis - Energy-Requiring Reactions

Glycolysis – Energy-Releasing Phase  

During this phase, each three-carbon sugar is transformed into another three-carbon molecule, pyruvate, by a sequence of events. Two ATP molecules and one NADH molecule are formed in these processes. Because this step occurs twice, once for each of the two three-carbon sugars, it generates four ATP and two NADH in total.  

Glycolysis - Energy-Releasing Phase

Each process in glycolysis is catalyzed by its own enzyme. An essential enzyme for glycolysis control is phosphofructokinase, which catalyzes the synthesis of the unstable two-phosphate sugar molecule fructose-1, 6-bisphosphate. Phosphofructokinase regulates glycolysis by speeding up or slowing it down in response to the cell’s energy demands. 

Complete glycolysis

Why do certain reactions release energy while others take energy from their surroundings? 


  • If the reactant molecules in a given reaction have more energy than the product molecules, energy is released into the environment in the form of heat and light. When this happens, the process is known as an exothermic reaction. 
  • If the product molecules have more energy than the reactants, the reaction draws energy from the environment. When this happens, the process is known as an endothermic reaction.  
Exothermic Reaction
Endothermic Reaction


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