OCR Module 5 Energy respiration essential notes

Question 1

Describe the processes in the cell that require energy

Answer 1

1. Active transport (carrier proteins, endocytosis and exocytosis)
2. Anabolic reactions (biosynthesis reactions such as DNA replication, transcription and translation)
3. Movement (cilia, flagella, muscle contraction)

Question 2

Describe the structure of ATP (and ADP)

Answer 2

1. ATP is adenosine triphosphate A pentose sugar, ribose
2. Joined by glycosidic bond to an adenine nitrogenous base on C1
3. Joined by ester bond to three phosphate groups on C5

Question 3

Explain how ATP synthesis and hydrolysis are related to its role as an energy storage molecule

Answer 3

1. ATP is synthesised by adding a phosphate group to ADP
2. Adding the third phosphate group requires an energy input
3. The energy to synthesise ATP usually comes from respiration
4. ATP is hydrolysed by removing the third phosphate group This releases energy
5. The energy released can be provided to active cellular processes

Question 4

Summarise how the reactions in respiration produce ATP

Answer 4

1. Complex organic molecules can be used in respiration (carbohydrate (monosaccharides), lipids (fatty acids) and proteins (amino acids))
2. These molecules are broken down (oxidised) to simpler inorganic molecules
3. Energy released can be used to synthesis ATP directly (substrate-level phosphorylation)
4. The hydrogens are used to create a proton gradient which drives ATP synthesis by ATP synthase (oxidative phosphorylation)

Question 5

Describe the main structures of the mitochondrion and, where applicable, their role in respiration

Answer 5

Question 6

State the four stages of aerobic respiration and where in the cell they occur

Answer 6

1. Glycolysis occurs in the cytoplasm
2. The link reaction occurs in the matrix of the mitochondria The Krebs cycle occurs in the matrix of the mitochondria Oxidative phosphorylation occurs in the inner mitochondrial membrane (cristae)

Question 7

Describe the events of glycolysis

Answer 7

1. Glycolysis is a metabolic pathway occurring in the cytoplasm
2. In step one, glucose is phosphorylated into hexose bisphosphate
3. Then split into two 3-carbon triose phosphates (two ATP molecules are used)
4. In step two, triose phosphate is oxidised to pyruvate (3C)
5. The hydrogens extracted are transferred to NAD to form NADH (dehydrogenation)
6. Four ATP are also produced here (substrate-level phosphorylations)
7. The net gain of glycolysis is two pyruvate, two NADH and two ATP

Question 8

Describe the events o f the link reaction

Answer 8

1. The pyruvate enters the matrix of the mitochondria
2. The 3C pyruvate is decarboxylated to 2C acetyl units
3. Pyruvate is simultaneously dehydrogenated
4. The hydrogen is transferred to NAD forming NADH
5. The acetyl unit is transferred to coenzyme A, forming acetyl coenzyme A
6. For each glucose, two Acetyl-CoA will be produced

Question 9

Summarise the events of the Krebs cycle

Answer 9

1. The Krebs cycle is a metabolic pathway that occurs in the matrix of the mitochondria
2. 2C Acetyl is decarboxylated to carbon dioxide
3. Dehydrogenation steps produce NADH and FADH
4. Substrate level phosphorylation also produces ATP

Question 10

Describe the formation of citrate in the Krebs cycle

Answer 10

1. Acetyl-CoA is used to transfer 2C acetyl to 4C oxaloacetate
2. This results in the formation of 6C citrate The regenerated coenzyme A returns to the link reaction

Question 11

Describe the formation of oxaloacetate in the Krebs cycle

Answer 11

1. 6C Citrate is converted to 4C oxaloacetate in a number of separate enzyme reactions
2. Two carboxylation reactions occur, each producing a molecule of carbon dioxide
3. Four dehydrogenation reactions occur, producing three NADH and one FADH
4. One substrate-level phosphorylation also occurs, producing an ATP molecule

Question 12

State what a coenzyme is

Answer 12

1. Coenzymes are organic, non-protein molecules that are required to form the active enzyme
2. They associate non-permanently with the enzyme
3. In respiration the coenzymes are coenzyme A, NAD and FAD

Question 13

Describe the roles of coenzymes in respiration

Answer 13

1. Coenzyme A transfers acetyl from the Link reaction to the Krebs cycle
2. NAD and FAD transfer hydrogen to the electron transport chain
3. NAD and FAD pick up hydrogen (become reduced) in dehydrogenation steps (glycolysis, link reaction and Krebs cycle)
4. They deliver hydrogen to the electron transport chain to become reoxidised
5. When NAD and FAD are oxidised, they are able to collect more hydrogen again

Question 14

Explain the relationship between vitamins and coenzymes

Answer 14

Question 15

Summarise the events of oxidative phosphorylation

Answer 15

1. Oxidative phosphorylation occurs at the inner mitochondrial membrane
2. The reduced coenzymes NADH and FADH deliver electrons to the electron carriers of the electron transport chain
3. Electron flow through the ETC is used to build a proton gradient
4. The proton gradient is used to synthesise ATP
5. Each NADH results in 3 ATP produced
6. Each FADH results in 2 ATP produced

Question 16

Describe how the proton gradient is established

Answer 16

1. Reduced coenzymes deliver hydrogen to the electron carriers
2. Hydrogen is split into electrons and protons
3. The electrons pass along the ETC, which provides energy for pumping protons from the matrix to the intermembrane space
4. Electrons are accepted from the final electron carrier by oxygen
5. With the addition of protons, this results in the formation of water

Question 17

Describe how proton gradient is used to synthesise ATP

Answer 17

1. There is a higher concentration of protons in the intermembrane space compared to the matrix
2. The inner mitochondrial membrane is impermeable to protons except for at the ATP synthase
3. Protons diffuse down the concentration gradient through ATP synthase
4. The release of energy is used by ATP synthase to phosphorylate ADP to ATP in the matrix

Question 18

Explain how a lack o f oxygen affects ATP production in respiration

Answer 18

1. Intense muscle contraction requires ATP at a rate that uses up oxygen faster than it can be supplied.
2. Without oxygen as the final electron acceptor, oxidative phosphorylation stops.
3. Oxidised NAD and FAD coenzymes are not regenerated for the preceding stages
4. So Kreb’s cycle and Link reaction also stop

Question 19

Describe anaerobic respiration in animals

Answer 19

1. Glycolysis is the only step that can continue without oxygen
2. Because an alternative reaction regenerates NAD
3. Pyruvate is converted to lactic acid by the enzyme lactate dehydrogenase
4. In this step, NADH is oxidised back to NAD
5. Which is recycled to maintain glycolysis
6. And maintain ATP production
7. Though much lower ATP production per glucose molecule used (wouldn’t sustain the animal in the long term)

Question 20

Describe the consequences of prolonged anaerobic respiration in mammals

Answer 20

1. Anaerobic respiration results in the build-up of lactic acid
2. Anaerobic respiration also results in a much lower ATP yield
3. The build-up of lactic acid, lowers pH
4. This can affect the tertiary structure of proteins and reduce functionality
5. If ATP supply does not meet demands then this could reduce function of muscles (contraction) as well as other tissues and organs

Question 21

Explain how the ‘oxygen debt’ concept relates to the fate of lactic acid

Answer 21

1. Lactic acid is toxic and eventually must be removed
2. Lactic acid can be converted to pyruvate and metabolised to carbon dioxide in the liver in the presence of oxygen Therefore, the build-up of lactic acid is the build-up of an
3. ‘oxygen debt’
4. Once the exercise is complete and oxygen supply returns, that oxygen is used to remove lactic acid
5. Thus, heavy breathing may continue even after exercise is completed

Question 22

Describe anaerobic respiration in yeast

Answer 22

1. In yeast and plants, anaerobic respiration is also achieved through maintaining glycolysis
2. Pyruvate is decarboxylated to ethanal
3. Ethanal is then reduced by NADH regenerating NAD

Question 23

Describe how the rate of respiration can be measured in yeast

Answer 23

1. Place yeast in a sugar solution in a test tube or flask
2. Attach a gas syringe, or delivery tube with inverted measuring cylinder to measure the volume of gas evolved
3. As the yeast respire, the glucose is oxidised to carbon dioxide
4. The attached gas syringe or delivery tube with measuring cylinder can be used to measure the carbon dioxide evolved
5. A stopwatch/timer can be used to determine the rate of carbon dioxide production
6. An oil barrier can be placed on top of the yeast suspension to produce anaerobic conditions

Question 24

Identify the molecules that can be used as respiratory substrates

Answer 24

1. Glucose
2. Lactic acid
3. Complex carbohydrates (starch in plants, glycogen in animals)
4. Lipids
5. Amino acids
6. Ketone bodies

Question 25

Describe how glycogen can be used for respiration

Answer 25

1. In the liver and muscle
2. During starvation/fight or flight response
3. Glycogen can be hydrolysed to glucose (glycogenolysis)
4. Glucose then enters the glycolysis pathway
5. The maximum amount of ATP is produced

Question 26

Describe how lactic acid can be used for respiration

Answer 26

1. Lactic acid is transported to the liver from anaerobically respiring tissues
2. Lactate is converted into pyruvate
3. Pyruvate can then enter the Link reaction in the mitochondria
4. Slightly less ATP produced as ATP is not gained from glycolysis

Question 27

Describe how Lipids can be used for respiration

Answer 27

1. In all tissues except brain
2. Triglycerides can be hydrolysed to glycerol and fatty acids during starvation
3. Glycerol can be converted to pyruvate and enter the Link reaction (ATP from glycolysis lost)
4. The fatty acids can be converted to acetyl-coA and enter the Krebs cycle (no ATP from glycolysis)

Question 28

Describe how amino acids can be used for respiration

Answer 28

1. Amino acids from diet or protein breakdown in other tissues arrive in the blood at the Liver
2. Amino acids are converted to pyruvate
3. Pyruvate enters the Link reaction
4. No ATP from glycolysis

Question 29

Describe how ketone bodies can be used f or respiration

Answer 29

1. the brain cannot use lipids for respiration
2. During starvation the liver converts fatty acids into small molecules called ketone bodies
3. These leave the liver in the blood and enter brain cells
4. In the brain cells, ketone bodies are converted into acetyl-CoA
5. acetyl-CoA enters the krebs cycle

Question 30

Compare the energy values of carbohydrates, lipids and proteins, and suggest an explanation for the differences

Answer 30

1. Carbohydrate respiration (eg glucose) produces 38 molecules of ATP
2. Carbohydrates and protein have a similar energy value
3. Lipids have a much higher energy value
4. This is because lipids have more C-H bonds / more hydrogen Which can produce more reduced coenzymes for oxidative phosphorylation

Question 31

Describe an experimental setup t hat would allow you to investigate respiration rates

Answer 31

1. A respirometer
2. With respiring organisms in one tube, and a control tube with no respiring organisms
3. The two tubes connected by tube with fluid, which moves depending on the gas pressure
4. The setup can be repeated but with a range of temperatures, substrates and substrate concentrations for respiring organisms

Question 32

Describe how you would measure the r ate of oxygen consumption using a respirometer

Answer 32

1. Add potassium hydroxide to the tube with respiring organisms
2. This absorbs the carbon dioxide evolved
3. As oxygen is consumed, it reduces the pressure and moves the fluid towards the organisms
4. The volume of oxygen consumed in a certain amount of time is the rate of respiration

Question 33

Describe how you would measure the r ate of carbon dioxide production

Answer 33

1. Once the rate of oxygen consumption is known (above)
2. Repeat the experiment without potassium hydroxide
3. The carbon dioxide production is the difference between the new rate and previous oxygen consumption rate