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OCR Biology Paper 1 > 5.7 - Respiration > Flashcards

5.7 - Respiration Flashcards

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1
Q

Define cell respiration

A

Controlled release of energy from organic compounds to produce ATP

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2
Q

Explain why organisms need to respire

A

Provide energy in the form of ATP for:
- Active transport
- Anabolic reactions (e.g. building proteins from amino acids)
- Movement (e.g. cilia, flagella, muscles)

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3
Q

Write the word equation for aerobic respiration

A

Glucose + Oxygen → Carbon dioxide + Water

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4
Q

Write the symbol equation for aerobic respiration

A

C6H12O6 + 6O2 → 6CO2 + 6H2O

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5
Q

Where does aerobic respiration take place?

A
  • Mitochondria
  • Glycolysis occurs in cytosol
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6
Q

Describe the structure of the matrix

A
  • Fluid found inside mitochondrion
  • Contains enzymes needed in link reaction and Krebs cycle
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7
Q

What does the inner mitochondrial membrane contain?

A

Contains electron transport chain and ATP synthase (oxidative phosphorylation)

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8
Q

What is the cristae?

A
  • Folds of inner mitochondrial membrane
  • Increases surface area for oxidative phosphorylation
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9
Q

What does the outer mitochondrial membrane do?

A

Separates contents of mitochondrion from the rest of the cell

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10
Q

Describe how the structure of a mitochondrion is related to its function

A
  • Intermembrane space between inner and outer membrane allows for a proton gradient to develop
  • Cristae give large surface area for ATP synthesis
  • ATP synthase generates ATP from ADP + phosphate
  • Electron transport chains for generating a proton gradient
  • Matrix contains enzymes for Krebs cycle
  • Ribosomes and DNA for protein synthesis
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11
Q

What is phosphorylation?

A

Transfer of a phosphate group to a molecule (e.g. hexose)
- Makes the molecule less stable and more reactive
- Prevents diffusion out of the cell
- Phosphate can be transferred from ATP or as inorganic phosphate (Pi)

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12
Q

List the stages of aerobic respiration

A
  • Glycolysis
  • Link reaction
  • Krebs cycle
  • Oxidative phosphorylation
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13
Q

What is the substrate in glycolysis?

A

Glucose

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14
Q

Where does glycolysis take place?

A

Cell cytoplasm

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15
Q

Outline the process of glycolysis

A
  • Takes place in cytoplasm/cytosol
  • Glucose is phosphorylated
  • Two molecules of ATP are used
  • Produces hexose bisphosphate
  • Hexose sugar converted into two (3C) triose phosphate molecules (lysis)
  • 3C molecules oxidised to form pyruvate
  • Small net gain of two ATP
  • Formed by substrate-level phosphorylation
  • Net gain of two NADH (reduced NAD)
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16
Q

Summarise the link reaction

A
  • Pyruvate produced by glycolysis is absorbed by mitochondrion
  • Enzymes in matrix of mitochondrion remove hydrogen and carbon dioxide from pyruvate
  • Removal of hydrogen is oxidation
  • Removal of carbon dioxide is decarboxylation
  • Whole process = oxidative decarboxylation
  • Hydrogen accepted by NAD+ to form reduced NAD (NADH)
  • Product is an acetyl group
  • Acetyl group is attached to Coenzyme A to form Acetyl CoA
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17
Q

Where does the link reaction take place?

A

Mitochondrial matrix

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18
Q

From which substrate is the first carbon dioxide molecule released during cellular respiration?

A

Pyruvate

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19
Q

Outline the role of coenzyme A in aerobic respiration

A
  • Binds to acetyl group
  • Passes acetyl group to Krebs cycle
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20
Q

Outline the Krebs cycle

A
  • Occurs in the mitochondrial matrix
  • Series of enzyme controlled reactions that break down Acetyl CoA into CO2
  • Acetyl group (2C) from Acetyl CoA combines with oxaloacetate (4C) to make citrate (6C)
  • Citrate is decarboxylated and oxidised to give a 5C compound, CO2 and reduced NAD
    (NADH)
  • Further decarboxylation and oxidation gives the 4C compound oxaloacetate, CO2, NADH,
    reduced FAD (FADH2) and ATP
  • ATP produced by substrate-level phosphorylation
  • Oxaloacetate combines with a new molecule of acetyl CoA and cycle starts again
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21
Q

What name is given to the removal of a hydrogen from a compound?

A

Dehydrogenation

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22
Q

Name one compound that undergoes dehydrogenation during the Krebs cycle

A

Citrate

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23
Q

Define substrate level phosphorylation

A

Production of ATP from ADP
- Via transfer of a phosphate group from a reactive intermediate

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24
Q

In which stages of respiration does substrate level phosphorylation occur?

A
  • Glycolysis
  • Krebs cycle
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25
Q

Explain the difference between substrate level phosphorylation and oxidative phosphorylation

A

Substrate level
- Direct transfer of phosphate group
- From a reactive intermediate
- Occurs in glycolysis and Krebs cycle
- Produces small amounts of ATP

Oxidative
- Requires electron transport, chemiosmosis and ATP synthase
- Inorganic phosphate added to ADP
- Produces large amounts of ATP

26
Q

What are NADH and FADH2?

A

Coenzymes

27
Q

What is the role of NADH and FADH2 in aerobic cell respiration?

A
  • Electron carriers
  • Provide electrons and H+ required for chemiosmosis
  • Produced in glycolysis, link reaction and Krebs cycle
28
Q

Where is the electron transport chain located?

A

Mitochondrial inner membrane (cristae)

29
Q

What is the role of electron transport chain?

A
  • Proteins in the inner mitochondrial membrane
  • Energy from electrons used to pump protons into intermembrane space
  • Establishes proton gradient across inner membrane
30
Q

What is the role of ATP synthase?

A
  • Enzyme located in inner mitochondrial membrane
  • Energy released as protons diffuse down the gradient through ATP synthase
  • ATP synthase converts ADP to ATP
31
Q

What is the final electron acceptor in oxidative phosphorylation?

A
  • Oxygen
  • Combines with an electron and H+ ions to form water
32
Q

Explain how oxidative phosphorylation occurs by means of chemiosmosis

A
  • Electrons from NADH/FADH2 passed along electron transport system in inner membrane of
    mitochondria
  • Energy released as electrons move from one carrier to next
  • Carrier is oxidised as it loses an electron to the next carrier, which becomes
    reduced
  • Energy released during electron transport causes proton pumping
  • H+ pumped against concentration gradient from matrix to intermembrane space
  • H+ provided by NADH and FADH2
  • H+ diffuses down concentration gradient back through ATP synthase
  • Passage of H+ through ATP synthase causes production of ATP from ADP + Pi
33
Q

When is the majority of ATP produced during aerobic respiration?

A
  • Oxidative phosphorylation
  • Produces ~32 ATP molecules per 1 glucose molecule
34
Q

What are the products of aerobic respiration?

A
  • Carbon dioxide
  • Water
35
Q

Why does aerobic respiration yield fewer molecules of ATP than the theoretical maximum?

A
  • Some ATP used to transport pyruvate into mitochondrion
  • Some energy released in electron transport chain is not used to transport H+
  • Not all the H+ movement back across membrane is used to generate ATP
  • Not all the NADH is used to feed into the electron transport chain
36
Q

When does anaerobic respiration occur?

A

When no oxygen is present

37
Q

Which stage is common to both aerobic and anaerobic respiration?

A

Glycolysis
- Takes place in cytoplasm
- Does not require oxygen
- Small net gain of ATP

38
Q

Define anaerobic respiration

A
  • Doesn’t require oxygen
  • Gives small yield of ATP from glucose
  • Allows cellular processes to continue (e.g. active transport)
    Products:
  • Lactate (humans)
  • Ethanol + carbon dioxide (yeast)
39
Q

Give the word equation for anaerobic respiration in animals

A

Glucose → Lactate

40
Q

Describe what happens to pyruvate during anaerobic respiration in an animal cell

A
  • Pyruvate produced by glycolysis
  • Pyruvate accepts hydrogen from NADH
  • Catalysed by lactate dehydrogenase
  • NAD+ regenerated
  • Allows glycolysis to continue
  • Limited amount ATP can continue to be produced
  • Pyruvate converted to lactate
  • No oxygen to act as final electron acceptor
  • Link reaction, Krebs cycle and oxidative phosphorylation cannot take place
41
Q

Why is it necessary for NAD+ to be regenerated during anaerobic respiration in an animal cell?

A
  • Limited amount of NAD+ in the cell
  • Regeneration of NAD+ allows glycolysis to continue
  • Some ATP can continue to be formed
42
Q

Why can anaerobic respiration in animal cells not continue indefinitely?

A
  • Reduced quantity of ATP produced not sufficient to maintain vital processes
  • Lactic acid causes pH to fall
  • Leads to proteins denaturing
  • e.g. respiratory enzymes, muscle filaments
43
Q

Where is lactate (lactic acid) converted back into glucose?

A
  • Liver
  • Carried there in the blood
44
Q

What is required to convert lactic acid into glucose?

A

Oxygen

45
Q

Define oxygen debt

A

The oxygen required to convert the lactic acid built up into glucose

46
Q

Explain why anaerobic respiration produces less ATP than aerobic respiration

A
  • In anaerobic respiration:
  • Conversion of glucose into pyruvate during glycolysis occurs
  • Produces 2 molecules of ATP (net)
  • Only substrate level phosphorylation occurs
  • Oxygen not available as final electron acceptor
  • Pyruvate (animals) and ethanal (yeast) used to regenerate NAD+ for glycolysis
  • Krebs cycle and oxidative phosphorylation do not occur
47
Q

Give the word equation for anaerobic respiration in yeast

A

Glucose → Ethanol + Carbon dioxide

48
Q

Describe the process of anaerobic respiration in yeast

A
  • Non-reversible
  • Pyruvate converted to ethanal
  • Catalysed by pyruvate decarboxylase
  • Ethanal accepts hydrogen atom from NADH
  • Converts ethanal to ethanol
  • NAD+ regenerated for glycolysis to continue
49
Q

Why can anaerobic respiration in yeast cells not continue indefinitely?

A
  • Ethanol is toxic to yeast cells
  • Yeast unable to survive if levels rise too high
50
Q

Explain why the anaerobic respiration pathway in animal cells can be reversed, but the anaerobic respiration pathway in yeast cells cannot

A

In animals:
- Pyruvate is converted lactic acid
- Can be reversed as no other product formed
- Lactate dehydrogenase enzyme can reverse the reaction

In yeast
- Pyruvate converted to ethanol and carbon dioxide
- Cannot be reversed as carbon dioxide is lost
- Decarboxylase enzyme cannot reverse the reaction

51
Q

Describe the use of yeast in the baking industry

A
  • Yeast is added to flour at the start of the baking process
  • Aerobic respiration of yeast produces carbon dioxide
  • Carbon dioxide bubbles help dough rise
52
Q

Describe the use of yeast in the brewing and biofuels industry

A
  • Fermentation
  • Anaerobic respiration of yeast produces ethanol and carbon dioxide
  • Yeast die when ethanol concentration reaches 15%
53
Q

Define respiratory substrate

A

Molecule that can be used in respiration to produce ATP

54
Q

What is the primary respiratory substrate?

A

Glucose

55
Q

What other molecules can be used as respiratory substrates?

A
  • Lipids
  • Proteins
56
Q

Explain how lipids can be used as respiratory substrates

A

Triglycerides hydrolysed to fatty acids and glycerol
- Fatty acids enter the Krebs cycle
- Glycerol converted to pyruvate

57
Q

Explain how proteins can be used as respiratory substrates

A
  • Hydrolysed into amino acids
  • Amino acids deaminated in liver
  • Remaining molecule enters respiratory pathway
  • As pyruvate
  • Process requires ATP
  • Reduces net production of ATP
58
Q

Why do lipids produce more ATP than glucose during respiration?

A

Lipids contain greater proportion of carbon-hydrogen bonds

59
Q

Why aren’t fats and proteins used as the substrate in glycolysis?

A
  • Lipids are harder to transport and digest (although will yield more energy per gram)
  • Proteins release potentially toxic nitrogenous compounds when broken down
  • Deamination and conversion to pyruvate requires ATP
60
Q

How is the respiratory quotient calculated?

A

RQ = CO2 produced / O2 consumed

OCR Biology Paper 1 (20 decks)

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