Chapter 3 Respiration

Question 1

What are oxidation reactions?

Answer 1

The loss of electrons

Question 1

What are reduction reactions?

Answer 1

The gain of electrons

Question 2

Relate structure of mitochondrion to function

Answer 2

Cristae - large SA for reactions
Matrix - contains enzymes for Krebs cycle
H+ carriers - needed for chemiosmosis/ETC
Permeable outer membrane - enables entry of pyruvate

Question 4

What is oxidative phosphorylation?

Answer 4

The energy for making ATP comes from oxidation-reduction reactions and is released in the transfer of electrons along a chain of electron carrier molecules.

Question 5

Why do plants respire?

Answer 5

Energy in the form of ATP is generated, which is needed for active transport and metabolic activity.

Question 6

What is photophosphorylation?

Answer 6

The energy for making ATP comes from light and is released in the transfer of electrons along a chain of electron carrier molecules.

Question 6

What is substrate-level phosphorylation?

Answer 6

When phosphate groups are transferred from donor molecules to ADP to make ATP with no oxygen required.

Question 7

Define dehydrogenation

Answer 7

The removal of one or more hydrogen atoms from a molecule.

Question 7

What is decarboxylation?

Answer 7

The removal of a carboxyl group from a molecule, releasing carbon dioxide

Question 8

Define respiratory substrate

Answer 8

An organic substance that can be used for respiration

Question 10

What are the 4 stages of aerobic respiration?

Answer 10

Glycolysis
Link reaction
Krebs cycle
Electron transport chain

Question 11

Where does glycolysis occur?

Answer 11

In the cytoplasm of the cell.

Question 12

What happens in glycolysis?

Answer 12

Glucose is phosphorylated by 2 molecules of ATP. This makes a hexose biphosphate. The fructose biphosphate splits into 2 triose phosphates that are then dehydrogenated. The hydrogen atoms transfer to coenzyme NAD producing reduced NAD. The 4 phosphates left over combine with 4 ADP’s to form 4 molecules of ATP. 2 molecules of pyruvic acid is also produced as a result of substrate-level phosphorylation.

Question 12

What is the function of FAD in respiration?

Answer 12

FAD accepts H ions and then donate them to set up the H ion gradient in chemiosmosis

Question 13

Where does the Link reaction occur?

Answer 13

Mitochondrial matrix

Question 13

What does NAD do in respiration?

Answer 13

NAD accepts H ions and then acts as a source of H ions for the electron transport chain

Question 15

What happens in the link reaction?

Answer 15

Pyruvate diffuses into the mitochondrial matrix. The pyruvate is dehydrogenated and the hydrogen is accepted by NAD to form reduced NAD. The pyruvate is also decarboxylated. The 2-carbon acetate group remaining from the glucose combines with coenzyme A to form acetyl coenzyme A.

Question 17

Where does the Krebs cycle occur?

Answer 17

Mitochondrial matrix

Question 18

Where is hexose biphosphate formed?

Answer 18

In glycolysis, in the cytosol outside the mitochondrion

Question 19

What happens in the Krebs cycle?

Answer 19

Acetyl coenzyme A (2-C) combine with oxaloacetate (4-C acid) to form citrate (6-C acid). The citrate is dehydrogenated and decarboxylated. CO2 and NADH is formed with a 5-C acid. The 5-C acid is dehydrogenated and decarboxylated. 1 molecule of CO2, 2 molecules of NADH and 1 molecule of FADH2 are formed with a 4-C acid. Substrate level phosphorylation occurs and ATP is produced.

Question 21

How many carbon atoms in acetate?

Answer 21

2

Question 22

How many carbon atoms in citrate?

Answer 22

6

Question 23

How is citrate made from acetate?

Answer 23

Citrate (6C) is made in the Krebs cycle by the combination of Acetyl coenzyme A (2C) and oxaloacetate (4C)

Question 24

What is produced in the Krebs cycle?

Answer 24

1 ATP by substrate level phosphorylation
3 molecule of NADH
1 molecule of FADH2
2 molecules of CO2

Question 25

Where does the electron transport chain (ETC) occur?

Answer 25

On the Cristae (inner membrane of mitochondria)

Question 26

What happens in the ETC?

Answer 26

Hydrogen from reduced NAD and FAD splits into hydrogen ions and electrons. The electrons get passed from one carrier to the next. Each movement releases enough energy to power the pumping of H+ ions across the membrane into the inter-membrane space. An electrochemical gradient is created from the build up of H+ ions in the inter membrane space. H+ ions pass down the electrochemical gradient through a stalked particle containing ATP synthetase (chemiosmosis). Oxygen is the final acceptor of the hydrogen which produces water.

Question 27

For each molecule of glucose entering glycolysis, how many NADH and FADH2 does the ETC receive?

Answer 27

10 NADH | 2 FADH2

Question 28

How much ATP is produced at the end of the Aerobic respiration?

Answer 28

2 net ATP molecules are made during glycolysis, 2 made during the Krebs cycle. During ETC for every 2 FADH2 makes 4 ATP molecules and for every 10 NADH makes 30 ATP molecules. Therefore, a total of 38 ATP molecules are synthesised.

Question 30

What happens during anaerobic respiration in animals?

Answer 30

Glycolysis still occurs (glucose is broken down into pyruvate). The pyruvate becomes the hydrogen acceptor and is converted into lactate (lactic acid). This process is reversible, so that when oxygen becomes available again, the lactate can be broken down into carbon dioxide and water, releasing the energy it contains.

Question 31

What happens during anaerobic respiration in microorganisms?

Answer 31

Glycolysis occurs (glucose is broken down into pyruvate). The pyruvate is decarboxylated and converted into CO2 and ethanal (a hydrogen acceptor). Ethanal is reduced by accepting hydrogen from NADH converting it into ethanol (in alcoholic fermentation). This is not reversible and ethanol cannot be broken down if oxygen is available, it accumulates in the cells and can rise to toxic concentrations.

Question 34

What is the final electron acceptor in aerobic respiration?

Answer 34

Oxygen - H+ ions and electrons combine with oxygen to form water

Question 37

Describe the process of anaerobic respiration in yeast

Answer 37

Glucose is broken down into pyruvate and ATP is produced. Pyruvate is converted to ethanal and then to ethanol.

Question 38

Describe the process of anaerobic respiration in mammals

Answer 38

Glucose is broken down into pyruvate. Coenzyme NAD is reduced and ATP is formed. Pyruvate is converted to lactate (lactic acid) NAD is produced from reduced NAD

Question 41

Explain the difference in relative energy values of carbohydrates, lipids and protein respiratory substrates.

Answer 41

The energy released is proportional to the relative numbers of hydrogen and oxygen atoms in the substrate, the more hydrogen for chemiosmosis, the greater the number of ATP that can be generated

Question 42

Describe how the rate of respiration can be investigated practically

Answer 42

Rate of respiration can be investigated by measuring volume of Carbon Dioxide produced. By capturing and measuring CO2 the factors that increase CO2 production can also be investigated

Question 45

Describe the evidence for chemiosmosis

Answer 45

Low pH in the inter membrane space

Question 46

Outline the process of chemiosmosis

Answer 46

Reduced NAD & FAD donate H+ ions, which are pumped across the Cristae into the inter membrane space. This sets up a proton gradient. As the H+ ions diffuse back into the matrix via a stalked particle combined with ATP synthetase, ATP is formed

Question 47

Compare anaerobic respiration in mammals and in yeast

Answer 47

Anaerobic respiration in yeast produces ethanol, in mammals they generate lactic acid.

Question 50

Explain why the theoretical maximum yield of ATP per molecule of glucose is rarely achieved in aerobic respiration

Answer 50

Not all H+ ions are used in chemiosmosis (some may leak out) ATP is also used in respiration and so the net ATP production will be less than the theoretical depending on how much ATP is used.