Respiration

Question 1

4 stages of aerobic respiration

Answer 1

Glycolysis
Link reaction
Krebs cycle
Oxidative phosphorylation

Question 2

Features of aerobic respiration

Answer 2

Produces water & carbon dioxide & more ATP.

Question 3

Features of anaerobic respiration

Answer 3

In animals, it produces lactate. In plants & fungi, it produces ethanol & carbon dioxide. Less ATP.

Question 4

What are coenzymes?

Answer 4

Molecules required for the functioning of certain enzymes, e.g., by carrying H atoms between molecules.

Question 5

3 examples of coenzymes

Answer 5

FAD: KREBS CYCLE.
NADP: PHOTOSYNTHESIS.
NAD: works with DEHYDROGENASE ENZYMES that catalyse the removal of H atoms from substrates and transfer them to other molecules involved in OXIDATIVE PHOSPHORYLATION.

Question 6

How does glycolysis provide indirect evidence for evolution?

Answer 6

It is a universal feature of all living organisms; it is the 1st step of both aerobic and anaerobic respiration.

Question 7

Where does glycolysis occur?

Answer 7

In the cytoplasm of all living cells.

Question 8

Summary of glycolysis

Answer 8

Splitting the hexose glucose molecule into 2 triose pyruvate molecules.

Question 9

Describe the 1st step of glycolysis.

Answer 9

Phosphorylation of glucose to glucose phosphate: glucose is activated/made more reactive by the addition of 2 phosphate molecules.

Question 10

In the first step of glycolysis, where do the 2 phosphate molecules for the phosphorylation of glucose come from?

Answer 10

They come from the hydrolysis of 2 ATP molecules to ADP. This provides a lower activation energy for the subsequent enzyme-controlled reactions and the energy to activate glucose.

Question 11

2nd step of glycolysis

Answer 11

Each phosphorylated glucose molecule is split into 2 triose phosphate molecules.

Question 12

3rd step of glycolysis: oxidation of triose phosphate

Answer 12

Hydrogen is removed from each of the triose phosphate molecules & transferred to NAD (a hydrogen carrier molecule) to form reduced NAD.

Question 13

4th step of glycolysis: the production of ATP

Answer 13

Enzyme-controlled reactions convert each triose phosphate molecule into 3-carbon pyruvate molecules. 2 molecules of ATP are regenerated from ADP in the process.

Question 14

What are the overall products of glycolysis?

Answer 14

2 molecules of pyruvate.
2 molecules of reduced NAD.
Net increase of 2 molecules of ATP.

Question 15

Summary of the link reaction

Answer 15

The triose pyruvate molecules undergo a series of reactions to form 2-carbon acetylcoenzyme A.

Question 16

Where does the link reaction occur?

Answer 16

The matrix of mitochondria.

Question 17

Overall word equation for the link reaction

Answer 17

Pyruvate + NAD + CoA —> Acetylcoenzyme A + reduced NAD + CO2
Via series of reactions.

Question 18

Describe the link reaction in detail.

Answer 18

• The 2 molecules of pyruvate from glycolysis are actively transported into the matrix of the mitochondria.
• The pyruvate is oxidised to acetate. The 3-carbon pyruvate loses a CO2 + 2H.
• The 2H are accepted by NAD to form reduced NAD.
• The 2-carbon acetate combines with coenzyme A to form acetylcoenzyme A.

Question 19

Where does the Krebs cycle occur?

Answer 19

The matrix of mitochondria.

Question 20

Summary of the Krebs cycle.

Answer 20

Acetylcoenzyme A is introduced to a cycle of oxidation-reduction reactions that yield some ATP & lots of reduced NAD & FAD.

Question 21

1st stage of the Krebs cycle

Answer 21

2-carbon acetylcoenzyme A combines with a 4-carbon molecule to form a 6-carbon molecule.

Question 22

2nd stage of the Krebs cycle

Answer 22

Via series of reactions, this 6-carbon molecule loses CO2 & hydrogen to give a 4-carbon molecule & a single molecule of ATP, produced by substrate-level phosphorylation.

Question 23

3rd step of the Krebs cycle

Answer 23

The 4-carbon molecule can now combine again with a new molecule of acetylcoenzyme A. The cycle restarts…

Question 24

Why is Krebs cycle important?

Answer 24

• It breaks down macromolecules into smaller ones.
• It produces H atoms, which are carried by NAD to the electron transfer chain to provide energy to produce ATP for oxidative phosphorylation.
• It regenerates the 4-carbon molecule that combines with acetylcoenzyme A, which would otherwise accumulate.
• It is a source of intermediate compounds used by cells in the manufacture of fatty acids, amino acids & chlorophyll.

Question 25

How does ATP release energy?

Answer 25

The negative charges mean ATP is unstable. The bonds between the phosphates are weak, so can be easily broken.

Question 26

Summary of oxidative phosphorylation

Answer 26

Electrons associated with reduced NAD & FAD are released from the Krebs cycle to synthesise ATP. H2O is a by-product.

Question 27

What is obtained from 1 molecule of pyruvate?

Answer 27

- Reduced coenzymes NAD & FAD, which can provide energy to produce ATP molecules by oxidative phosphorylation. - 1 ATP molecule. - 3 CO2 molecules. 1 glucose produces 2 pyruvate, so double the above per glucose.

Question 28

Where does oxidative phosphorylation occur?

Answer 28

The inner, folded membrane/ cristae where the necessary enzymes & other proteins are.

Question 29

1st stage of oxidative phosphorylation

Answer 29

The H atoms produced by glycolysis & the Krebs cycle combine with NAD & FAD.

Question 30

2nd stage of oxidative phosphorylation

Answer 30

The reduced NAD & FAD donate electrons to the 1st molecule in the electron transfer chain.

Question 31

3rd stage of oxidative phosphorylation

Answer 31

As electrons pass along a chain of electron transfer chain carrier molecules in a series of oxidation-reduction reactions, the energy they release causes the active transport of protons across the inner mitochondrial membrane and into the inter-membranes space.

Question 32

4th stage of oxidative phosphorylation

Answer 32

The protons accumulate in the intermembranal space before they diffuse back into the mitochondrial matrix through ATP synthase channels embedded in the mitochondrial membrane. The flow of H+ causes the shape of the ATP synthase channel to change.

Question 33

What happens at the end of the electron transfer chain in oxidative phosphorylation?

Answer 33

The electrons combine with these protons & oxygen to form water. Oxygen is the final acceptor of electrons in the electron transfer chain.

Question 34

Summary of oxidative phosphorylation

Answer 34

Mechanism whereby some of the energy of the electrons within the H atoms is conserved by ATP formation.

Question 35

What is the importance of oxygen in respiration?

Answer 35

- To acts as the final acceptor of H atoms produced in glycolysis & the Krebs cycle at the end of the ETC. - Without oxygen removing H atoms at the end of the chain, protons (H+) & electrons would back up along the chain, and respiration would come to a halt as the Krebs cycle & the ETC cannot combine once all the FAD & NAD are reduced.

Question 36

What is the purpose of an electron transfer chain?

Answer 36

Each carrier molecule is at a slightly lower energy level, so electrons move down an energy gradient. This releases energy gradually, so more can be used by the organism instead of lost as heat as with large energy changes in a single step.

Question 37

Mitochondria in more metabolically active cells

Answer 37

There are more mitochondria, & cristae are more densely packed to increase surface area.

Question 38

How is energy from cellular respiration derived?

Answer 38

Glycolysis & the Krebs cycle involve substrate level phosphorylation, which is the direct transfer of a phosphate from a respiratory intermediate to ADP to produce ATP. Oxidative phosphorylation in the electron transfer chain: indirect linking of energy from the phosphate to ADP to produce ATP, involving energy from H atom carriers or NAD & FAD.

Question 39

What is required for glycolysis to continue?

Answer 39

It produces pyruvate & hydrogen that must be constantly removed. The hydrogen must be released from reduced NAD to regenerate NAD in order to take up the hydrogen atom produced in glycolysis.

Question 40

How is NAD replenished?

Answer 40

The pyruvate molecule from glycolysis accepts the hydrogen from reduced NAD.

Question 41

Why do lipids release more than twice the energy of the same mass of carbohydrate?

Answer 41

Oxidation of lipids produces 2-carbon fragments of carbohydrate and many hydrogen atoms. The H atoms are used to produce ATP in oxidative phosphorylation.

Question 42

1st stage in the respiration of lipids

Answer 42

Lipids are hydrolysed to fatty acids & glycerol.

Question 43

What happens to the glycerol once lipids have been hydrolysed in the respiration of lipids?

Answer 43

The glycerol is phosphorylated & converted to triose phosphate which enters the glycolysis pathway & then Krebs cycle.

Question 44

What happens to the fatty acid once lipids have been hydrolysed in the respiration of lipids?

Answer 44

The fatty acid is broken into 2-carbon fragments, which are converted into acetylcoenzyme A. This enters the Krebs cycle.

Question 45

Describe the respiration of proteins.

Answer 45

Protein is hydrolysed into its amino acids. Their amino groups are removed by deamination. They enter the respiratory pathway at different points depending on their number of carbon atoms. 3-carbon compounds are converted into pyruvate. 4- & 5-carbon compounds are converted to intermediates in the Krebs cycle.

Question 46

Anaerobic respiration in animals to overcome a temporary oxygen shortage

Answer 46

Pyruvate + NADH —> lactate + oxidised NAD NAD from glycolysis can accumulate and must be removed. Hence, each pyruvate molecule produced takes up 2 hydrogen atoms from the reduced NAD produced by glycolysis to form lactate.

Question 47

Lactate

Answer 47

Causes cramp & fatigue, if it accumulates in tissues. It is also an acid, so causes pH changes to enzymes.

Question 48

How is lactate removed?

Answer 48

The lactate is oxidised to pyruvate, which is then either further oxidised to release energy or converted to glycogen in the liver.

Question 49

Anaerobic respiration in some plants, some bacteria & fungi, e.g., yeast.

Answer 49

Pyruvate + NADH —> ethanol + CO2 + oxidised NAD The pyruvate molecule formed at the end of glycolysis loses a molecule of CO2 & accepts H from reduced NAD to produce ethanol.

Question 50

Where does the ATP produced in anaerobic respiration come from?

Answer 50

Glycolysis only as the pyruvate is converted into either lactate or ethanol, so cannot take part in the Krebs cycle.