C1.2  Cell Respiration

Theme:  Interaction and Interdependence

Interaction occurs when molecules collide and transform energy from one form to another.

• ATP is the "energy currency" that interacts with nearly every metabolic process. It transfers energy through the physical interaction of phosphorylation, where a phosphate group is moved to another molecule to "prime" it for work.
• Interaction occurs through the transfer of electrons and hydrogen between molecules. NAD acts as an electron carrier, interacting with enzymes in glycolysis and the Krebs cycle to pick up electrons, then interacting with the Electron Transport Chain (ETC) to drop them off.
• In the mitochondria, the interaction between high-energy electrons and the proteins of the ETC creates a physical gradient of protons across the inner membrane. This gradient then interacts with ATP synthase to drive the mechanical rotation that synthesizes ATP (chemiosmosis).

Cell respiration is not a standalone event but a system that is interdependent on other biological processes to function.

• Respiration is interdependent with nutrition and photosynthesis. It relies on a steady supply of carbon compounds (glucose, lipids, or proteins) to act as fuel. Without the products of photosynthesis or digestion, the respiratory "machinery" has no input.
  
• There is interdependence between catabolic reactions (like respiration, which breaks down glucose to charge ADP into ATP) and anabolic reactions (which use that ATP to build proteins, move muscles, or perform active transport). One cannot happen without the constant recycling provided by the other.
  
• The mitochondria demonstrate endosymbiotic interdependence with the rest of the cell. The cell depends on the mitochondria for aerobic ATP production, while the mitochondria depend on the cell for protection, raw materials (pyruvate), and the synthesis of many of its necessary proteins.
  
• Cellular respiration is chemically interdependent with gas exchange. Aerobic respiration requires a constant influx of oxygen and the removal of carbon dioxide. If the gas exchange system fails, the aerobic respiratory pathway will stop.
  

Guiding Questions:  
Guiding questions help students view the content of the syllabus through the conceptual lenses of both the themes and the levels of biological organization.

• What are the roles of hydrogen and oxygen in the release of energy in cells?
• How is energy distributed and used inside cells?

​
​Linking Questions:  
Linking questions strengthen students’ understanding by making connections between topics.  The ideal outcome of the linking questions is networked knowledge.

• In what forms is energy stored in living organisms?
• What are the consequences of respiration for ecosystems?

Key Terms to Know: * higher level only

Acetyl Group*
Acetyl-coA*
Active Transport
Adenosine Diphosphate (ADP)
Adenosine Triphosphate (ATP)
Aerobic Cell Respiration
Anabolism
Anaerobic Cell Respiration
ATP Synthase*
Carbohydrates*
Carbon Compound
Carbon Dioxide (CO2)*
Catalysis*
Cell Respiration
Chemiosmosis*
Citrate*
Coenzyme-A*
Cytoplasm

Decarboxylation*
Dehydrogenation*
Electron*
Electron Acceptor*
Electron Transport Chain*
Energy
Enzyme*
Fatty Acid
Gas Exchange
Glucose
Glycolysis*
Hydrogen*
Hydrolysis
Intermembrane Space*
Krebs Cycle*
Lactate*
Link Reaction*
Lipids*

Lysis*
Matrix*
Mitochondria
NAD*
Nucleotide
Oxaloacetate*
Oxidation Reaction*
Phosphate
Phosphorylation*
Proton*
Pyruvate*
Reaction Rate
Redox Reaction*
Reduced NAD*
Reduction Reaction*
Substrate
Yeast*

C1.2.1— ATP as the molecule that distributes energy within cells.

• Describe the structure of ATP.
• Outline properties of ATP that make it suitable for the use as an energy currency within cells. ​

C1.2.2— Life processes within cells that ATP supplies with energy.

• Outline example cellular processes that require use of ATP.

C1.2.3— Energy transfers during interconversions between ATP and ADP.

• Describe the ATP-ADP cycle, including the relative amount of energy and the roles of hydrolysis and phosphorylation.  
• State why heat is generated during the ATP-ADP cycle.

C1.2.4— Cell respiration as a system for producing ATP within the cell using energy released from carbon compounds.

• Define cellular respiration. 
• Distinguish between cellular respiration and gas exchange. 
• List reasons why cellular respiration must be continuously performed by all cells.
• List common substrates of cellular respiration. ​

C1.2.5— Differences between anaerobic and aerobic cell respiration in humans. ​

• Compare and contrast anaerobic fermentation and aerobic respiration.​

C1.2.6- Variables affecting the rate of cell respiration.

• Identify the manipulated (independent), responding (dependent) and controlled variation in experiments of variables affecting the rate of cell respiration.
• List three approaches for determining the rate of cellular respiration.
• Describe three investigative techniques for measuring the effect of a variable on the rate of cellular respiration.

AHL ​​​​C1.2.7- Role of NAD as a carrier of hydrogen and oxidation by removal of hydrogen during cell respiration.

• Outline oxidation and reduction reactions in terms of movement of hydrogen and electrons.
• Define “electron carrier.”
• State the name of the electron carrier molecule used in cellular respiration.
• Outline the formation of reduced NAD (=NADH + H+) during glycolysis.

AHL ​​​​C1.2.8- Conversion of glucose to pyruvate by stepwise reactions in glycolysis with a net yield of ATP and reduced NAD.

• State the formula for the glycolysis reaction.
• State that glycolysis occurs in both anaerobic and aerobic respiration.
• State the location of the glycolysis reaction in a cell. 
• State that glycolysis is an example of a metabolic pathway catalyzed by enzymes.
• Outline the glycolysis reaction, including phosphorylation of glucose, lysis, oxidation and ATP formation.
• State the net yield of ATP and reduced NAD produced in glycolysis.

AHL ​​​​C1.2.9- Conversion of pyruvate to lactate as a means of regenerating NAD in anaerobic cell respiration.

• State why NAD must be regenerated in anaerobic respiration.  
• Compare anaerobic respiration in yeasts and humans.
• Outline the process of regenerating NAD and production of lactate in humans during anaerobic respiration.
• State the condition in which humans would perform anaerobic respiration.

AHL ​​​​C1.2.10- Anaerobic cell respiration in yeast and its use in brewing and baking.

• Outline the process of regenerating NAD and production of ethanol in yeast during anaerobic respiration.
• Outline how anaerobic respiration in yeast is used in brewing and baking.

AHL ​​​C1.2.11- Oxidation and decarboxylation of pyruvate as a link reaction in aerobic cell respiration.

• Summarize the reactants and products of the link reaction.
• State that the link reaction occurs in the matrix of the mitochondrion.  
• Outline the link reaction with references to decarboxylation, oxidation and binding of CoA.

AHL ​​​C1.2.12- Oxidation and decarboxylation of acetyl groups in the Krebs cycle with a yield of ATP and reduced NAD.

• State that the Krebs cycle occurs in the matrix of the mitochondrion.  
• Outline the events of the Krebs cycle, referencing the formation of citrate from oxaloacetate, decarboxylation of citrate to reform oxaloacetate,  formatting of CO2, formation of ATP and the oxidation reactions that form reduced NAD (=NAD + H+) and reduced FAD (=FADH2).
• State that the reduced NAD and reduced FAD produced in the Krebs cycle carry  electrons to the mitochondrial electron transport chain. 
• List the net products of one turn of the Krebs cycle.

AHL ​​​C1.2.13-  Transfer of energy by reduced NAD to the electron transport chain in the mitochondrion.

• Outline the structure and function of the electron transport chain within a mitochondrion. 
• State that at the mitochondrial electron transport chain, reduced NAD  (=NAD + H+) and reduced FAD (=FADH2) are oxidized with the transfer electrons to electron carrier proteins.
• List the reactions that generated the reduced NAD (=NAD + H+) and reduced FAD (=FADH2) used in the electron transport chain.

AHL ​​​C1.2.14- Generation of a proton gradient by flow of electrons along the electron transport chain.

• Describe how the movement of electrons through the electron transport chain is used to generate a proton gradient in the intermembrane space.

AHL ​​​C1.2.15- Chemiosmosis and the synthesis of ATP in the mitochondrion.

• Define chemiosmosis.
• Describe the structure ATP synthase.
• Outline the formation of ATP by ATP synthesis, with reference to movement of protons and phosphorylation of ADP.
• Compare the total amount of ATP made from anaerobic and aerobic respiration. ​

AHL ​​​C1.2.16- Role of oxygen as terminal electron acceptor in aerobic cell respiration.

• State that oxygen is the final electron acceptor in the electron transport chain.
• Explain why aerobic respiration will stop if oxygen is not present. 
• State that the formation of water in the matrix at the end of the electron transport chain helps to maintain the proton gradient between the intermembrane space and the matrix.​

AHL ​​​C1.2.17- Differences between lipids and carbohydrates as respiratory substrates.

• Compare the use of carbohydrates and lipids as respiratory substrates in aerobic and anaerobic respiration.
• Explain the greater energy yield of lipids compared to carbohydrates when used as respiratory substrates. 
• Outline the process by which lipids can be a substrate for respiration. ​