3.5.2 Respiration
What happens to when there is insufficient oxygen?
Pyruvate is reduced to lactate/ethanol NAD regenerated from the oxidation of reduced NAD, so glycolysis can continue
Why is lactic acid produced as a result of anaerobic respiration?
Pyruvate reduced to form lactate
What is involved in anaerobic respiration?
Pyruvate reduced to lactate (in animals) and ethanol (in yeast) Reduced NAD oxidised back to NAD = NAD regenerated = can be used in glycolysis again
What is the importance of NADH in respiration?
Releases H+ ions + e-s... - So e-a can be used for e- transfer chain - So H+ ions can be transported to cristae
What process is ATP produced by?
Substrate-level phosphorylation
What is respiration?
The breakdown of glucose to produce ATP
What do other respiratory substrates include?
The breakdown products of lipids and amino acids, which enter the Krebs cycle
What is hydrolysis?
The breaking of a bond using water
What is a condensation reaction?
The forming of a chemical bond, releasing water
What is the equation for aerobic respiration?
glucose + oxygen -> carbon dioxide + water
What is substrate level phosphorylation?
An inorganic phosphate is donated to phosphorylase another compound
Is glycolysis aerobic or anaerobic?
Anaerobic (does not require oxygen)
What type of respiration takes place when oxygen isn't available?
Anaerobic respiration
What happens to pyruvate if respiration is only anaerobic?
Pyruvate converted to ethanol or lactate using reduced NAD The oxidised NAD produced in this way can be used in further glycolysis
What happens to pyruvate if respiration is aerobic?
Pyruvate from glycolysis enters the mitochondrial matrix by active transport
What are the steps for the Krebs cycle?
*PER ACETYL COENZYME A (THERE ARE TWO PRODUCED IN THE LINK REACTION)* 1) Acetyl coenzyme A (2C) reacts with a 4 carbon molecule 2) Coenzyme A released + 6 carbon molecule produced 3) 6C —> 5C CO2 released (decarboxylation) NAD reduced to reduced NAD 4) 5C —> 4C (4C molecule regenerated) CO2 released (decarboxylation) 2 NAD reduced to 2 reduced NAD FAD reduced to reduced FAD ADP + Pi —> ATP (substrate level phosphorylation) 5) Acetyl coenzyme A reacts with 4C molecule again + REPEAT 6) Turns twice for every molecule of glucose used in respiration
What are the steps of the link reaction?
*PER PYRUVATE MOLECULES (THERE ARE TWO PRODUCED IN GLYCOLYSIS)* 1) Pyruvate is pumped into the matrix of the mitochondria by active transport as it's small enough to pass through the membrane 2) Pyruvate is oxidised and decarboxylated to acetate NAD reduced to reduced NAD CO2 released (decarboxylation) —> released by the lungs during expiration 3) Acetate combines with coenzyme A to produce acetylcoenzyme A
The Respiratory Quotient (RQ) can provide information on the type of respiration taking place in an organism. The following equation is used to calculate the RQ. RQ = volume of CO2 produced during respiration/volume of O2 used during respiration A student calculated that the RQ of germinating seeds was 1.8. Use the information provided to explain this result. (2)
- Aerobic and anaerobic respiration occurring - More carbon dioxide produced than oxygen uptake
A student investigated the rate of gas exchange in aerobically respiring seeds using the apparatus shown in the diagram. She carried out two experiments. Both experiments were carried out at the same temperature. Explain why. (2)
- It affects enzymes - Enzymes control the rate of respiration
Aerobic respiration produces more ATP per molecule of glucose than anaerobic respiration. Explain why. (2)
- Oxygen is final/terminal electron acceptor/oxygen combines with electrons and protons - Aerobic respiration oxidative phosphorylation/electron transfer chain - Anaerobic respiration only glycolysis occurs/no Krebs/no link reaction
A student investigated the rate of gas exchange in aerobically respiring seeds using the apparatus shown in the diagram. She carried out two experiments. In Experiment 1, she put potassium hydroxide solution in the beaker. Potassium hydroxide solution absorbs carbon dioxide. In Experiment 2, she put water in the beaker. The level of coloured liquid in the right-hand side of the manometer tube went down during Experiment 1. Explain why. (3)
- the seeds produce CO2 but it's absorbed by KOH - seeds absorb O2 for aerobic respiration - -be pressure/drop in volume of gas
A student investigated the rate of gas exchange in aerobically respiring seeds using the apparatus shown in the diagram. She carried out two experiments. In Experiment 1, she put potassium hydroxide solution in the beaker. Potassium hydroxide solution absorbs carbon dioxide. In Experiment 2, she put water in the beaker. The student repeated Experiment 1 using seeds which were respiring anaerobically. What would happen to the level of coloured liquid in the right-hand side of the manometer tube? Explain your answer. (2)
- wouldn't change - oxygen isn't used for anaerobic respiration, meaning it's just CO2 that's being produced but this is absorbed by the KOH
What are the steps of glycolysis?
1) Glucose 2) 2 ATP —> 2 ADP Hydrolysis of 2 ATP and the phosphorylation of glucose = lowers Ea = easier to oxidise later 3) Glucose phosphate 4) 2 triose phosphate Per triose phosphate... 5) 2 ADP —> 2 ATP (substrate level phosphorylation) and NAD (coenzyme) —> reduced NAD Triose phosphate is oxidised to Pyruvate 6) Pyruvate actively transported into mitochondria matrix where the remaining reactions of respiration take place 7) net gain of ATP and reduced NAD
What are the main stages of aerobic respiration?
1) Glycolysis 2) Link reaction 3) Krebs cycle 4) Oxidative phosphorylation
What are the steps for oxidative phosphorylation?
1) the reduced coenzymes (reduced NAD + reduced FAD) release their hydrogens in the form of protons and electrons 2) these electrons enter the electron transfer chain, which is attached to the cristae 3) in a series of oxidation and reduction reactions, the electrons are passed down from a higher energy level to a lower one, releasing energy 4) this energy is used to pump the protons across the inner mitochondrial membrane to the jntermembranal space 5) the produces a higher conc of H+ here than in the matrix - CHEMIOSMOTIC GRADIENT 6) Protons can only diffuse down their gradient via the protein embedded in the membrane by facilitated diffusion 7) as they move through this enzyme (ATP synthase), the energy is shed to add a phosphate group to ADP to produce ATP 8) the electrons and protons combine with oxygen (the final/terminal electron acceptor) to make water
What is the net gain of ATP in glycolysis?
2 ATP
What are the reactants needed for the Krebs cycle (per molecule of glucose respired)?
2 Acetyl coenzyme A 6 NAD 2 FAD 2 ADP + Pi
What are the products of the link reaction?
2 CO2 2 reduced NAD 2 Acetyl coenzyme A
What are the products of glycolysis?
2 Pyruvate 2 ADP 4 ATP 2 reduced NAD
What are the reactants needed for the link reaction?
2 pyruvate 2 NAD 2 coenzyme A
Describe 3 important stages in glycolysis and the three important products?
2 pyruvate 2 reduced NAD Net gain of 2 ATP
What are the important products of the Krebs cycle (per molecule of glucose)?
2 reduced FAD 6 reduced NAD 4 CO2 2 ATP
What are the products of the Krebs cycle (per molecule of glucose respired)?
4 CO2 6 reduced NAD 2 reduced FAD 2 ATP
A student investigated the rate of gas exchange in aerobically respiring seeds using the apparatus shown in the diagram. She carried out two experiments. In Experiment 1, she put potassium hydroxide solution in the beaker. Potassium hydroxide solution absorbs carbon dioxide. In Experiment 2, she put water in the beaker. The results from both experiments are shown in the table. Use these results to calculate the volume of carbon dioxide produced during Experiment 1. (1)
4 cm-3
The Respiratory Quotient (RQ) can provide information on the type of respiration taking place in an organism. The following equation is used to calculate the RQ. RQ = volume of CO2 produced during respiration/volume of O2 used during respiration What would be the RQ for aerobic respiration of glucose? (1)
6 CO2 produced 6 O2 used 1
What does respiration produce?
ATP
Where are the enzymes which catalyse the reactions of glycolysis found?
Cytoplasm
Where does glycolysis occur?
Cytoplasm
How are proteins an example of other respiratory substrates?
Deaminate NH2 in liver Hydrolyse the peptide bonds to form 3C, 4C or 5C amino acids —> 3C used as pyruvate —> 4C/5C used in Krebs cycle
Why is there less energy produced from anaerobic respiration compared with aerobic respiration?
Fewer stages Most ATP made in oxidative phosphorylation but this doesn't occurs in anaerobic respiration - only glycolysis (net gain of 2 ATP)
What are the reactants needed for glycolysis?
Glucose 2 ATP 2 NAD 4 ADP
Explain why Krebs cycle turns twice for each molecule of glucose used in respiration?
Glucose is split into 2 Acetyl coenzyme A
What does glycolysis take place in the cytoplasm?
Glucose is too large to cross the mitochondrial membrane
What is the first stage of aerobic and anaerobic respiration?
Glycolysis
What is phosphorylation?
Increasing the reactivity of a substance by adding a phosphate group
Where does oxidative phosphorylation take place?
Inner mitochondrial membrane (the crista)
Why can pyruvate be pumped into the matrix of the mitochondria?
It's small enough to pass through the membrane
How are lipids an example of other respiratory substrates?
Lipids hydrolysed to fatty acids + glycerol Fatty acids hydrolysed to 2C compounds + converted to Acetyl coenzyme A Glycerol phosphorylated to triose phosphate during glycolysis
Where does the Krebs cycle take place?
Mitochondrial matrix
Where does the link reaction take place?
Mitochondrial matrix
Where does pyruvate come from?
Oxidation of triose phosphate
What happens to pyruvate when there is sufficient oxygen?
Oxidised + decarboxylated to acetate
What is the final/terminal electron acceptor in aerobic respiration?
Oxygen
What type of reactions are involved in glycolysis?
Phosphorylation Oxidation Reduction