C1.2 Cell respiration

Interaction and interdependence—Molecules
Standard level and higher level: 2 hours
Additional higher level: 3 hours

Guiding questions

Linking questions

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

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

SL and HL

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  

 

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

Include the full name of ATP (adenosine triphosphate) and that it is a nucleotide. Students should appreciate the properties of ATP that make it suitable for use as the energy currency within cells.

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

Include active transport across membranes, synthesis of macromolecules (anabolism), movement of the whole cell or cell components such as chromosomes

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

Students should know that energy is released by hydrolysis of ATP (adenosine triphosphate) to ADP (adenosine diphosphate) and phosphate, but energy is required to synthesize ATP from ADP and phosphate. Students are not required to know the quantity of energy in kilojoules, but students should appreciate that it is sufficient for many tasks in the cell.

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

Students should appreciate that glucose and fatty acids are the principal substrates for cell respiration but that a wide range of carbon/organic compounds can be used. Students should be able to distinguish between the processes of cell respiration and gas exchange

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

Include which respiratory substrates can be used, whether oxygen is required, relative yields of ATP, types of waste product and where the reactions occur in a cell. Students should be able to write simple word equations for both types of respiration, with glucose as the substrate. Students should appreciate that mitochondria are required for aerobic, but not anaerobic, respiration

C1.2.6—Variables affecting the rate of cell respiration

Application of skills: Students should make measurements allowing for the determination of the rate of cell respiration. Students should also be able to calculate the rate of cellular respiration from raw data that they have generated experimentally or from secondary data

HL

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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

Students should understand that oxidation is a process of electron loss, so when hydrogen with an electron is removed from a substrate (dehydrogenation) the substrate has been oxidized. They should appreciate that redox reactions involve both oxidation and reduction, and that NAD is reduced when it
accepts hydrogen.

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

Include phosphorylation, lysis, oxidation and ATP formation. Students are not required to know the names of the intermediates, but students should know that each step in the pathway is catalysed by a different enzyme.

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

Regeneration of NAD allows glycolysis to continue, with a net yield of two ATP molecules per molecule of glucose.

C1.2.10—Anaerobic cell respiration in yeast and its use in brewing and baking

Students should understand that the pathways of anaerobic respiration are the same in humans and yeasts apart from the regeneration of NAD using pyruvate and therefore the final products.

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

Students should understand that lipids and carbohydrates are metabolized to form acetyl groups (2C), which are transferred by coenzyme A to the Krebs cycle.

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

Students are required to name only the intermediates citrate (6C) and oxaloacetate (4C). Students should appreciate that citrate is produced by transfer of an acetyl group to oxaloacetate and that oxaloacetate is regenerated by the reactions of the Krebs cycle, including four oxidations and two decarboxylations. They should also appreciate that the oxidations are dehydrogenation reactions

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

Energy is transferred when a pair of electrons is passed to the first carrier in the chain, converting reduced NAD back to NAD. Students should understand that reduced NAD comes from glycolysis, the link reaction and the Krebs cycle.

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

Students are not required to know the names of protein complexes

C1.2.15—Chemiosmosis and the synthesis of ATP in the mitochondrion

Students should understand how ATP synthase couples release of energy from the proton gradient with phosphorylation of ADP.

C1.2.16—Role of oxygen as terminal electron acceptor in aerobic cell respiration

Oxygen accepts electrons from the electron transport chain and protons from the matrix of the mitochondrion, producing metabolic water and allowing continued flow of electrons along the chain

C.1.2.17—Differences between lipids and carbohydrates as respiratory substrates

Include the higher yield of energy per gram of lipids, due to less oxygen and more oxidizable hydrogen and carbon. Also include glycolysis and anaerobic respiration occurring only if carbohydrate is the substrate, with 2C acetyl groups from the breakdown of fatty acids entering the pathway via acetyl-CoA
(acetyl coenzyme A).

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