What is respiration?
- A set of metabolic reactions that take place in organisms and break down respiratory substances, such as glucose, into smaller inorganic molecules, like water and carbon dioxide.
- Linked to the synthesis of ATP.
Why is respiration described as a catabolic process?
Complex molecules (respiratory substrates) are broken down into smaller, simpler molecules.
Why do organisms need to respire?
- Produces chemical energy in ATP for a variety of processes including active transport, metabolic reactions and muscle contraction.
- Releases heat energy for thermoregulation.
Define aerobic respiration.
A form of cellular respiration that takes place in the presence of oxygen and produces carbon dioxide, water and ATP.
Name the four main stages of aerobic respiration and state where they occur.
- Glycolysis (cytoplasm).
- Link reaction (mitochondrial matrix).
- Krebs cycle (mitochondrial matrix).
- ETC (inner mitochondrial membrane).
Outline the stages of glycolysis.
- Glucose (hexose sugar) phosphorylated to hexose bisphosphate by 2x ATP.
- Hexose bisphosphate splits into 2x triose phosphate (TP).
- 2 molecules of TP oxidised to 2x pyruvate.
Net gain of 2x reduced NAD (NADH) and 2x ATP per glucose.
Write an equation to summarise glycolysis.
Glucose + 2NAD + 2ADP + 2Pi = 2 pyruvate + 2NADH + 2ATP + heat.
How does pyruvate from glycolysis enter the mitochondria.
Via active transport.
Outline the link reaction.
- Oxidative decarboxylation and dehydrogenation of pyruvate to form acetate.
Net gain of carbon dioxide and 2x reduced NAD. - Acetate combines with coenzyme A (CoA) to form acetyl coenzyme A.
Write an equation to summarise the link reaction.
Pyruvate + NAD + CoA = acetyl CoA + reduced NAD + CO2.
What is the Krebs cycle?
A series of oxidation-reduction reactions in the matrix of the mitochondria in which acetyl coenzyme A is oxidised generating reduced NAD, reduced FAD, ATP and carbon dioxide.
What is the function of the Krebs cycle?
It is a means of releasing energy from carbon bonds to provide ATP, reduced NAD and reduced FAD (with the release of carbon dioxide) for the ETC
How many reduced NAD and reduced FAD does the complete oxidation of one glucose molecule yield?
- 10 reduced NAD
- 2 reduced FAD
What is the electron transport chain?
A series of electron carrier proteins that transfer electrons in a chain of oxidation-reduction reactions, releasing energy.
What happens in the ETC?
- Electrons released from reduced NAD and FAD undergo successive redox reactions.
- The energy released is coupled to maintaining the proton gradient or is released as heat.
- Oxygen acts as the final electron acceptor.
Describe the role of reduced NAD and reduced FAD in the ETC.
They are a source of electrons and protons.
How does chemiosmosis produce ATP during aerobic respiration?
- Protons flow down their concentration gradient from the intermembrane space into the mitochondrial matrix via ATP synthase.
- ATP synthase phosphorylates ADP to form ATP as protons flow through it.
State the role of oxygen in the ETC.
Final electron acceptor.
How many ATP are produced per oxidised NAD in aerobic respiration?
3 ATP
How many ATP are produced per oxidised FAD in aerobic respiration?
2 ATP
Define anaerobic respiration.
A form of cellular respiration that takes place in the absence of oxygen. Less ATP is formed than in aerobic respiration.
State the product of anaerobic respiration in animals.
Lactic acid.
Outline anaerobic respiration in animals.
- Only glycolysis continues.
- Reduced NAD (product of glycolysis) transfers the H to pyruvate, forming lactic acid and regenerating NAD.
- Catalysed by enzyme lactate dehydrogenase.
State the products of anaerobic respiration in plants and microorganisms,
Ethanol and carbon dioxide.
