12.1 Energy
12.2 Respiration
Energy is a fundamental concept in biology. All living things require a source of cellular energy to drive their various activities. ATP is the universal energy currency as its molecules are small, soluble and easily hydrolysed to release energy for cellular activities. All organisms respire to release energy from energy- rich molecules such as glucose and fatty acids and transfer that energy to ATP. Respiration is a series of enzyme-catalysed reactions that release energy in small ‘packets’. In eukaryotes, aerobic respiration occurs in mitochondria.
Learning outcomes
Candidates should be able to:
12.1 Energy
ATP is the universal energy currency as it provides the immediate source of energy for cellular processes.
a) outline the need for energy in living organisms, as illustrated by anabolic reactions, such as DNA replication and protein synthesis, active transport, movement and the maintenance of body temperature
b) describe the features of ATP that make it suitable as the universal energy currency
c) explain that ATP is synthesised in substrate-linked reactions in glycolysis and in the Krebs cycle
d) outline the roles of the coenzymes NAD, FAD and coenzyme A in respiration
e) explain that the synthesis of ATP is associated with the electron transport chain on the membranes of mitochondria and chloroplasts (see 12.2g)
f) explain the relative energy values of carbohydrate, lipid and protein as respiratory substrates and explain why lipids are particularly energy-rich
g) define the term respiratory quotient (RQ) and determine RQs from equations for respiration
h) 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.
This process of ATP synthesis using the energy in proton gradients is common to both respiration and photosynthesis.
Some organisms and some tissues are able to respire in both aerobic and anaerobic conditions. When yeast and plants respire under anaerobic conditions, they produce ethanol and carbon dioxide
as end-products; mammalian muscle tissue produces lactate when oxygen is in short
supply.
a) list the four stages in aerobic respiration (glycolysis, link reaction, Krebs cycle and oxidative phosphorylation) and state where each occurs in eukaryotic cells
b) outline glycolysis as phosphorylation of glucose and the subsequent splitting of fructose 1,6-bisphosphate (6C) into two triose phosphate molecules, which are then further oxidised to pyruvate with a small yield of ATP and reduced NAD
c) explain that, when oxygen is available, pyruvate is converted into acetyl (2C) coenzyme A in the link reaction
d) outline the Krebs cycle, explaining that oxaloacetate (a 4C compound) acts as an acceptor of the 2C fragment from acetyl coenzyme A to form citrate (a 6C compound), which is reconverted to oxaloacetate in a series of small steps
e) explain that reactions in the Krebs cycle involve decarboxylation and dehydrogenation and the reduction of NAD and FAD
f) outline the process of oxidative phosphorylation including the role of oxygen as the final electron acceptor (no details of the carriers are required)
g) explain that during oxidative phosphorylation:
• energetic electrons release energy as they pass through the electron transport system
• 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 required)
h) carry out investigations to determine the effect of factors such as temperature and substrate concentration on the rate of respiration of yeast using a redox indicator (e.g. DCPIP or methylene blue)
i) describe the relationship between structure and function of the mitochondrion using diagrams and electron micrographs
j) distinguish between respiration in aerobic and anaerobic conditions in mammalian tissue and in yeast cells, contrasting the relative energy released by each (a detailed account of the total yield of ATP from the aerobic respiration of glucose is not required)
k) explain the production of a small yield of ATP from respiration in anaerobic conditions in yeast and in mammalian muscle tissue, including the concept of oxygen debt
l) explain how rice is adapted to grow with its roots submerged in water in terms of tolerance to ethanol from respiration in anaerobic conditions and the presence of aerenchyma
m) carry out investigations, using simple respirometers, to measure the effect of temperature on the respiration rate of germinating seeds or small invertebrates
Energy is a fundamental concept in biology. All living things require a source of cellular energy to drive their various activities. ATP is the universal energy currency as its molecules are small, soluble and easily hydrolysed to release energy for cellular activities. All organisms respire to release energy from energy- rich molecules such as glucose and fatty acids and transfer that energy to ATP. Respiration is a series of enzyme-catalysed reactions that release energy in small ‘packets’. In eukaryotes, aerobic respiration occurs in mitochondria.
Learning outcomes
Candidates should be able to:
12.1 Energy
ATP is the universal energy currency as it provides the immediate source of energy for cellular processes.
a) outline the need for energy in living organisms, as illustrated by anabolic reactions, such as DNA replication and protein synthesis, active transport, movement and the maintenance of body temperature
b) describe the features of ATP that make it suitable as the universal energy currency
c) explain that ATP is synthesised in substrate-linked reactions in glycolysis and in the Krebs cycle
d) outline the roles of the coenzymes NAD, FAD and coenzyme A in respiration
e) explain that the synthesis of ATP is associated with the electron transport chain on the membranes of mitochondria and chloroplasts (see 12.2g)
f) explain the relative energy values of carbohydrate, lipid and protein as respiratory substrates and explain why lipids are particularly energy-rich
g) define the term respiratory quotient (RQ) and determine RQs from equations for respiration
h) 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.
This process of ATP synthesis using the energy in proton gradients is common to both respiration and photosynthesis.
Some organisms and some tissues are able to respire in both aerobic and anaerobic conditions. When yeast and plants respire under anaerobic conditions, they produce ethanol and carbon dioxide
as end-products; mammalian muscle tissue produces lactate when oxygen is in short
supply.
a) list the four stages in aerobic respiration (glycolysis, link reaction, Krebs cycle and oxidative phosphorylation) and state where each occurs in eukaryotic cells
b) outline glycolysis as phosphorylation of glucose and the subsequent splitting of fructose 1,6-bisphosphate (6C) into two triose phosphate molecules, which are then further oxidised to pyruvate with a small yield of ATP and reduced NAD
c) explain that, when oxygen is available, pyruvate is converted into acetyl (2C) coenzyme A in the link reaction
d) outline the Krebs cycle, explaining that oxaloacetate (a 4C compound) acts as an acceptor of the 2C fragment from acetyl coenzyme A to form citrate (a 6C compound), which is reconverted to oxaloacetate in a series of small steps
e) explain that reactions in the Krebs cycle involve decarboxylation and dehydrogenation and the reduction of NAD and FAD
f) outline the process of oxidative phosphorylation including the role of oxygen as the final electron acceptor (no details of the carriers are required)
g) explain that during oxidative phosphorylation:
• energetic electrons release energy as they pass through the electron transport system
• 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 required)
h) carry out investigations to determine the effect of factors such as temperature and substrate concentration on the rate of respiration of yeast using a redox indicator (e.g. DCPIP or methylene blue)
i) describe the relationship between structure and function of the mitochondrion using diagrams and electron micrographs
j) distinguish between respiration in aerobic and anaerobic conditions in mammalian tissue and in yeast cells, contrasting the relative energy released by each (a detailed account of the total yield of ATP from the aerobic respiration of glucose is not required)
k) explain the production of a small yield of ATP from respiration in anaerobic conditions in yeast and in mammalian muscle tissue, including the concept of oxygen debt
l) explain how rice is adapted to grow with its roots submerged in water in terms of tolerance to ethanol from respiration in anaerobic conditions and the presence of aerenchyma
m) carry out investigations, using simple respirometers, to measure the effect of temperature on the respiration rate of germinating seeds or small invertebrates
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