Biology A Level Edexcel B, Topic 5 (Respiration and
Photosynthesis) Questions And Answers
What is ATP?
Adenosine triphosphate; 'energy currency of cell'; used throughout cell, e.g. for
active transport in cell membrane, protein synthesis at ribosomes and contraction of
proteins in cilia; hydrolysed to produce ADP and Pi (inorganic phosphate group),
releasing energy due to high energy bond
Overall equation for respiration
C6H12O6 + 6O2 -> 6CO2 + 6H2O (+energy)
Why is the overall equation for respiration a simplification?
It is a multistage reaction - it's a series of metabolic pathways
Where does respiration occur?
In cytoplasm then (in aerobic conditions) in mitochondria
What are the 3 stages of aerobic respiration?
Glycolysis, link reaction and krebs cycle
What are the 2 ways of producing ATP?
1. Substrate level phosphorylation - coupled with reaction which releases energy
needed to convert ADP to ATP
2. Using hydrogen carriers - reduce hydrogen carriers (NAD or FAD); produce ATP
via oxidative phosphorylation; N.B. NAD & FAD are derivatives of B vitamins
Glycolysis
- Occurs in cytoplasm
- Metabolic pathway controlled by enzymes
- Anaerobic process
- 4 distinct stages:
1. Activation of glucose - by addition of 2 phosphate groups; uses 2 ATP
2. Lysis/splitting - catalysed by hydrolase enzyme; produce 3 carbon molecule
glycerate-3-phosphate (GP)
3. Oxidation - by reduction of NAD to NADH+H+; Pi is accepted simultaneously
4. ATP production - 4 ATP produced overall (2 from each molecule), forming
pyruvate(/pyruvic acid)
, Overall: gross yield = 4 ATP
net yield = 2 ATP (and 2 NADH+H+)
Structure of the mitochondria
- 2 membranes: outer mitochondrial membrane is smooth continuous capsule; inner
is highly folded (folds = cristae) giving huge surface area
- Space between membranes = intermembrane space
- Mitochondrial matrix - contains DNA and ribsomes
- Inner membrane has stalk particles - contain ATPase enzymes
Link reaction
- Occurs in mitochondrial matrix
- Decarboxylation (removal of CO2) from pyruvate
- Oxidation by NAD
- Forms acetyl coenzyme A
Krebs cycle
- Occurs in mitochondrial matrix
- Catalysed by oxidoreductase enzymes
- 4 carbon molecule combines w acetyl CoA to form 6 carbon molecule
- 2 CO2 molecules are released to reform 4 carbon molecule
- Each turn generates: 3 NADH+H+, 1 FADH+H+ and 1 ATP
- ATP generated by substrate level phosphorylation
- Cycle turns twice per glucose
What is produced overall in aerobic respiration?
ATP: 4 (2 from G, 2 from KC)
NADH+H+: 10 (2 from G, 2 from LR, 6 from KC)
FADH2: 2 (from KC)
CO2: 6 (2 from LR, 4 from KC)
Oxidative phosphorylation
- Occurs across inner mitochondrial membrane
- Generates ATP from O2 and NADH+H+/FADH2
- 'The production of ATP using energy derived from the redox reactions of an
electron transport chain'
What is the electron transfer chain?
- Made up of proteins called cytochromes, which contain iron
- Along chain, each protein is more strongly oxidising than the one before; O2 drives
Photosynthesis) Questions And Answers
What is ATP?
Adenosine triphosphate; 'energy currency of cell'; used throughout cell, e.g. for
active transport in cell membrane, protein synthesis at ribosomes and contraction of
proteins in cilia; hydrolysed to produce ADP and Pi (inorganic phosphate group),
releasing energy due to high energy bond
Overall equation for respiration
C6H12O6 + 6O2 -> 6CO2 + 6H2O (+energy)
Why is the overall equation for respiration a simplification?
It is a multistage reaction - it's a series of metabolic pathways
Where does respiration occur?
In cytoplasm then (in aerobic conditions) in mitochondria
What are the 3 stages of aerobic respiration?
Glycolysis, link reaction and krebs cycle
What are the 2 ways of producing ATP?
1. Substrate level phosphorylation - coupled with reaction which releases energy
needed to convert ADP to ATP
2. Using hydrogen carriers - reduce hydrogen carriers (NAD or FAD); produce ATP
via oxidative phosphorylation; N.B. NAD & FAD are derivatives of B vitamins
Glycolysis
- Occurs in cytoplasm
- Metabolic pathway controlled by enzymes
- Anaerobic process
- 4 distinct stages:
1. Activation of glucose - by addition of 2 phosphate groups; uses 2 ATP
2. Lysis/splitting - catalysed by hydrolase enzyme; produce 3 carbon molecule
glycerate-3-phosphate (GP)
3. Oxidation - by reduction of NAD to NADH+H+; Pi is accepted simultaneously
4. ATP production - 4 ATP produced overall (2 from each molecule), forming
pyruvate(/pyruvic acid)
, Overall: gross yield = 4 ATP
net yield = 2 ATP (and 2 NADH+H+)
Structure of the mitochondria
- 2 membranes: outer mitochondrial membrane is smooth continuous capsule; inner
is highly folded (folds = cristae) giving huge surface area
- Space between membranes = intermembrane space
- Mitochondrial matrix - contains DNA and ribsomes
- Inner membrane has stalk particles - contain ATPase enzymes
Link reaction
- Occurs in mitochondrial matrix
- Decarboxylation (removal of CO2) from pyruvate
- Oxidation by NAD
- Forms acetyl coenzyme A
Krebs cycle
- Occurs in mitochondrial matrix
- Catalysed by oxidoreductase enzymes
- 4 carbon molecule combines w acetyl CoA to form 6 carbon molecule
- 2 CO2 molecules are released to reform 4 carbon molecule
- Each turn generates: 3 NADH+H+, 1 FADH+H+ and 1 ATP
- ATP generated by substrate level phosphorylation
- Cycle turns twice per glucose
What is produced overall in aerobic respiration?
ATP: 4 (2 from G, 2 from KC)
NADH+H+: 10 (2 from G, 2 from LR, 6 from KC)
FADH2: 2 (from KC)
CO2: 6 (2 from LR, 4 from KC)
Oxidative phosphorylation
- Occurs across inner mitochondrial membrane
- Generates ATP from O2 and NADH+H+/FADH2
- 'The production of ATP using energy derived from the redox reactions of an
electron transport chain'
What is the electron transfer chain?
- Made up of proteins called cytochromes, which contain iron
- Along chain, each protein is more strongly oxidising than the one before; O2 drives
