StemUp: AQA A level Biology 3.5.2 Respiration

Why do we respire? (2)

- To produce ATP

- Which releases energy for cellular processes

What is ATP used for? (7)

- Active transport

- Synthesis reactions

- E.g. protein/DNA synthesis

- Muscle contraction

- Cell division

- Light independent reactions of photosynthesis

- First stage of glycolysis

What are the 4 stages of respiration? (4)

1. Glycolysis

2. Link reaction

3. Krebs Cycle

4. Electron Transport Chain (ETC)

What processes occur during glycolysis? (4)

1. Phosphorylation of glucose using ATP

2. Production of triose phosphate

3. Oxidation of triose phosphate to pyruvate

4. With a net gain of 2 ATP and 2 reduced NAD

What is the fate of pyruvate in anaerobic respiration? (3)

- Converted into ethanol or lactate

- Using reduced NAD

- The oxidised NAD produced in this way can be used in further glycolysis

What is the fate of pyruvate in aerobic respiration? (1)

Enters the mitochondrial matrix by active transport

What happens to pyruvate in the link reaction during aerobic respiration? (2)

1. Pyruvate is oxidised to acetate

2. Producing reduced NAD in the process

What does acetate combine with in the link reaction? (2)

1. Acetate combines with coenzyme A

2. To produce acetyl-coenzyme A

What happens during the Krebs cycle? (3)

1. Series of oxidation-reduction reactions occurs

2. Generates reduced coenzymes and ATP by substrate-level phosphorylation

3. Carbon dioxide is lost during krebs cycle

What is substrate-level phosphorylation? (4)

- Direct formation of ATP

- From ADP and Pi

- Using energy

- From the chemical processes occurring in the mitochondria

What is oxidative phosphorylation in simple terms? (2)

- The respiration equivalent of chemiosmotic theory (even the mark schemes align!!)

- Which produces ATP

NOTE: You will never be asked for this definition, this is just to help with the learning process

Describe oxidative phosphorylation (4)

1. Energy transferred during ETC is used to actively pump protons from the stroma into the thylakoid

2. A proton gradient is established

3. Protons then diffuse down their concentration gradient into the stroma via the enzyme ATP synthase

4.The energy transferred by the movement of protons is used to phosphorylate ADP to form ATP

What happens to the electrons after they have been pumped across the protons in oxidative phosphorylation? (3)

1. Accepted by the final acceptor oxygen

2. Electrons combine with a proton to form a hydrogen atom

3. Which then combines with oxygen to form water.

Malonate inhibits a reaction in the Krebs cycle

Explain why malonate would decrease the uptake of oxygen in a respiring cell. (2)

- No reduced NAD

- Oxygen is the final electron acceptor so less uptake in a respiring cell

What are some other respiratory substrates besides glucose that can be used? (2)

- The breakdown products of lipids and amino acids

- Which enter the Krebs cycle to produce ATP and reduced coenzymes

How many times do the Link reaction and krebs cycle occur per glucose molecule? (2)

- Twice per glucose molecule

- Because two pyruvate molecules are produced in glycolysis

What is the net production of ATP in aerobic respiration? (1)

38 ATP

How is the total ATP production distributed between glycolysis, ETC and the Krebs cycle? (3)

- Glycolysis produces 2 ATP per glucose (8 ATP in total as glycolysis occurs twice)

- ETC releases six ATP molecules

- The Krebs cycle produces 24 ATP in total