12. Energy and respiration

12.1 Energy

 ATP is the universal energy currency as it provides the immediate source of energy for cellular processes. 

1. outline the need for energy in living organisms, as illustrated by active transport, movement and anabolic reactions, such as those occurring in DNA replication and protein synthesis 

2. describe the features of ATP that make it suitable as the universal energy currency 

3. state that ATP is synthesised by: 

• transfer of phosphate in substrate-linked reactions 

• chemiosmosis in membranes of mitochondria and chloroplasts 

4. explain the relative energy values of carbohydrates, lipids and proteins as respiratory substrates 

5. state that the respiratory quotient (RQ) is the ratio of the number of molecules of carbon dioxide produced to the number of molecules of oxygen taken in, as a result of respiration

6.  calculate RQ values of different respiratory substrates from equations for respiration 

7. describe and carry out investigations, using simple respirometers, to determine the RQ of germinating seeds or small invertebrates (e.g. blowfly larvae) 

12.2 Respiration 

Respiration is the process whereby energy from complex organic molecules is transferred to ATP. 

1. State where each of the four stages in aerobic respiration occurs in eukaryotic cells: 

• glycolysis in the cytoplasm 

• link reaction in the mitochondrial matrix 

• Krebs cycle in the mitochondrial matrix 

• oxidative phosphorylation on the inner membrane of mitochondria 

2. outline glycolysis as phosphorylation of glucose and the subsequent splitting of fructose 1,6-bisphosphate (6C) into two triose phosphate molecules (3C), which are then further oxidised to pyruvate (3C), with the production of ATP and reduced NAD 

3. explain that, when oxygen is available, pyruvate enters mitochondria to take part in the link reaction 

4. describe the link reaction, including the role of coenzyme A in the transfer of acetyl (2C) groups 

5. outline the Krebs cycle, explaining that oxaloacetate (4C) acts as an acceptor of the 2C fragment from acetyl coenzyme A to form citrate (6C), which is converted back to oxaloacetate in a series of small steps 

6. explain that reactions in the Krebs cycle involve decarboxylation and dehydrogenation and the reduction of the coenzymes NAD and FAD

7.  describe the role of NAD and FAD in transferring hydrogen to carriers in the inner mitochondrial membrane 

8. explain that during oxidative phosphorylation: 

• hydrogen atoms split into protons and energetic electrons 

• energetic electrons release energy as they pass through the electron transport chain (details of carriers are not expected) 

• the released energy is used to transfer protons across the inner mitochondrial membrane 

• protons return to the mitochondrial matrix by facilitated diffusion through ATP synthase, providing energy for ATP synthesis (details of ATP synthase are not expected) 

• oxygen acts as the final electron acceptor to form water 

9. describe the relationship between the structure and function of mitochondria using diagrams and electron micrographs 

10. outline respiration in anaerobic conditions in mammals (lactate fermentation) and in yeast cells (ethanol fermentation) 

11.  explain why the energy yield from respiration in aerobic conditions is much greater than the energy yield from respiration in anaerobic conditions (a detailed account of the total yield of ATP from the aerobic respiration of glucose is not expected) 

12. explain how rice is adapted to grow with its roots submerged in water, limited to the development of aerenchyma in roots, ethanol fermentation in roots and faster growth of stems 

13. describe and carry out investigations using redox indicators, including DCPIP and methylene blue, to determine the effects of temperature and substrate concentration on the rate of respiration of yeast (link to save my exams notes).

14. describe and carry out investigations using simple respirometers to determine the effect of temperature on the rate of respiration