Chapter 7 Respiration

Question 1

What are phototrophs?

Answer 1

Organisms that can make their own energy using light and carbon dioxide via photosynthesis.

Question 2

What are heterotrophs?

Answer 2

Organisms that consume other plants or animals for energy.

Question 3

What is ATP hydrolysed to?

Answer 3

ADP and Pi (inorganic phosphate)

Question 4

What are the 4 stages of respiration?

Answer 4

1. Glycolysis
2. Link reaction
3. Krebs cycle
4. Oxidative phosphorylation

Question 5

What is the process of glycolysis?

Answer 5

1. 1 phosphoryl group is added to glucose to make hexose monophosphate and another is added to make hexose biphosphate (6C).
2. Glucose molecule splits into 2, 3C compounds - triose phosphate.
3. Each 3C compound is oxidised, producing pyruvate. This is controlled by enzyme-dehydrogenase and a co-enzyme NAD.
4. This process produces 2 ATP molecules from each triose phosphate group. 2 Hydrogen atoms are also removed by the coenzyme NAD, forming reduced NAD.

Question 6

What is the process of the Link reaction?

Answer 6

1. Pyruvate is decarboxylated - carboxyl group is removed CO2 is released.
2. Pyruvate is dehydrogenated - 2 hydrogens are removed and taken up by co-enzyme NAD producing reduced NAD. Acetyl group is produced.
3. The acetyl group combines with coenzyme A to become acetyl CoA, which carries the acetyl group to the Krebs cycle.

Question 7

Where do the link reaction and Krebs cycle take place?

Answer 7

Matrix of mitochondria

Question 8

Where does glycolysis take place?

Answer 8

Cytoplasm of the cell

Question 9

Where does oxidative phosphorylation take place?

Answer 9

Electron transport chains embedded in the cristae of the mitochondria (where there is a large surface area for electron carrier proteins and ATP synthase enzymes)

Question 10

What is the process of the Krebs Cycle?

Answer 10

1. The acetyl group (2C) combines with oxaloacetate (4C) to form citrate (6C).
2. Citrate is decarboxylated and dehydrogenated, producing a 5-carbon compound, 1 molecule of CO2 and 1 molecule of reduced NAD.
3. This 5C compound is decarboxylated and dehydrogenated, producing a 4C compound, 1 molecule if CO2 and 1 molecule of reduced NAD.
4. This 4C compound combines temporarily with CoA, producing 1 molecule of ATP through substrate level phosphorylation.
5. The 4C compound is dehydrogenated, producing 1 molecule of reduced FAD and catalysed by coenzyme flavine adenine dinucleotide.
6. The 4C compound is rearranged, catalysed by an isomerase enzyme. to produce oxaloacetate so the cycle can continue.

Question 11

How many turns of the Krebs cycle produce 1 molecule of glucose?

Answer 11

2

Question 12

How many molecules of reduced NAD, reduced FAD, carbon dioxide and ATP are produced by the links reaction for one molecule of glucose?

Answer 12

reduced NAD - 2
reduced FAD - 0
CO2 - 2
ATP - 0

Question 13

How many molecules of reduced NAD, reduced FAD, carbon dioxide and ATP are produced by the Krebs Cycle for one molecule of glucose?

Answer 13

reduced NAD - 6
reduced FAD - 2
CO2 - 4
ATP - 2

Question 14

What is produced by glycolysis?

Answer 14

4 ATP molecules, 2 reduced NAD molecules and 2 molecules of 3C Pyruvate.

Question 15

What is the process of oxidative phosphorylation?

Answer 15

1. Reduced NAD and reduced FAD are reoxidised and lose their H atoms.
2. The hydrogen atoms split into protons and electrons.
3. The protons go into the solution in the mitochondrial matrix.
4. The electrons pass along the electron transport chain made up of electron carrier proteins with iron cores. The electrons oxidise and reduce the iron core as they go.
5. These reaction release energy which is used to pump protons from the matrix into the intermembrane space.
6. This movement of protons creates a gradient across the membrane, generating a chemiosmotic potential also known as a proton motive force (pmf). They are a source of potential energy. ATP is made using the pmf.
7. The protons diffuse through the ATP synthase channels on the inner membrane. The flow of protons is known as chemiosmosis and causes a conformational change in the ATP synthase enzyme, allowing ADP and Pi to combine, forming ATP.
8. Oxygen is the final electron acceptor. It combines with electrons off the electron transport chain and protons diffusing down the ATP synthase channel, forming water. This equation is 4H+ + 4e- + O2 —> 2H2O

Question 16

How many ATP molecules are produced by oxidative phosphorylation?

Answer 16

28

Question 17

What happens in the absence of oxygen?

Answer 17

1. Oxygen cannot act as the final electron acceptor at the end of oxidative phosphorylation so protons diffusing through the ATP synthase channel cannot combine with electrons and oxygen to form water.
2. The concentration of protons increases in the matrix and reduces the proton gradient across the inner mitochondrial membrane.
3. Oxidative phosphorylation ceases.
4. Reduced NAD and reduced FAD are not able to unload their hydrogen atoms and cannot be reoxidised.
5. The Krebs cycle stops, as does the link reaction.

Question 18

What must happen for respiration to take place in the absence of oxygen?

Answer 18

Reduced NAD must be reoxidised

Question 19

What are the two ways in which reduced NAD can be reoxidised?

Answer 19

• The ethanol fermentation pathway
• The lactate fermentation pathway

Question 20

What is the process of the ethanol fermentation pathway?

Answer 20

1. Each molecule of pyruvate produced during glycolysis is decarboxylated and converted to ethanal. This is catalysed by pyruvate decarboxylase.
2. The ethanal accepts hydrogen atoms from reduced NAD, becoming reduced to ethanol. This is catalysed by ethanol dehydrogenase.
3. In the process, the reduced NAD is re-oxidised and made available to accept more hydrogen atoms from triose phosphate, thus allowing glycolysis to continue

Question 21

What is the process of the lactate fermentation pathway?

Answer 21

1.Pyruvate, produced in glycolysis, accepts hydrogen atoms from reduced NAD, also made in glycolysis. This is catalysed by lactate dehydrogenase. Pyruvate is reduced to lactate and the reduced NAD becomes reoxidised
2. The reoxidised NAD can accept more hydrogen atoms from triose phosphate during glycolysis and glycolysis can continue to produce enough ATP to sustain muscle contraction for a short period.

Question 22

What is the fate of lactate during anaerobic respiration?

Answer 22

The lactate produced in the muscle tissue is carried away from the muscles, in the blood, to the liver. When more oxygen is available the lactate may may be either:
- converted to pyruvate, which may enter the Krebs cycle via the link reaction
- recycled to glucose and glycogen

Question 23

What would happen if lactate were not removed from the muscle tissues in aerobic respiration?

Answer 23

The pH would be lowered, inhibiting the action of many of the enzymes involved in glycolysis and muscle contraction.

Question 24

How much ATP is produced from anaerobic respiration?

Answer 24

Ethanol fermentation and lactate fermentation don’t produce ATP. However, the net gain of 2 molecules of ATP per molecule of glucose is still obtained as glycolysis continues.

Question 25

What is a respiratory substrate?

Answer 25

An organic substance that can be oxidised by respiration, releasing energy to make molecules of ATP

Question 26

What are the 3 main respiratory substrates?

Answer 26

Carbohydrates, lipids & proteins

Question 27

How can carbohydrates be used respiration?

Answer 27

• poly/disaccharides can be hydrolysed to monosaccharides for respiration
• monosaccharides such as fructose, can be changed to glucose for respiration by isomerase enzymes

Question 28

How can lipids be used for respiration?

Answer 28

Triglycerides are hydrolysed by lipase to glycerol and fatty acids. Glycerol can then be converted to triose phosphate and respired

Question 29

How do you calculate the Respiratory Quotient (RQ)?

Answer 29

CO2 produced/ O2 consumed

Question 30

What is the RQ value when glucose is used?

Answer 30

1

Question 31

What is the RQ value when fatty acids are used?

Answer 31

0.7

Question 32

What is the RQ value when amino acids are used?

Answer 32

0.8

Question 33

How can proteins be used for respiration?

Answer 33

Excess amino acids released after the digestions of proteins are deaminated in the liver, producing the amino group and a keto acid. The keto acid enters the respiratory pathway as pyruvate, acetyl CoA or oxaloacetate.
When insufficient glucose or lipid are available during fasting/ prolonged exercise, protein from muscle can be hydrolysed to amino acids which are then respired. These amino acids may be converted to pyruvate or acetate and enter the Krebs cycle.

Question 34

How is a respirometer set up?

Answer 34

1. After placing a coloured fluid in the manometer tube, the apparatus is connected with the taps open, enabling the air in the apparatus to connect with the atmosphere.
2. The mass of living organisms to be used should be found
3. With the taps still open, the whole set-up is placed in a water bath for at least 10 minutes until it reaches the temperature of the water bath
4. The syringe plunger should be near the top of the scale on the syringe barrel and its level noted
5. The levels of the monometer can be marked/ recorded
6. The taps are closed and the apparatus is left for a set time
7. The change in level of the manometer liquid can be measured and the total volume of oxygen absorbed can be measured by depressing the syringe to reset the manometer
8. You can also calculate the volume of oxygen absorbed per minute by using the ‘length the manometer moved x pi x radius^2’

Question 35

How can a mammal hold their breath for significant periods of time underwater?

Answer 35

• have high lung capacity
• low metabolic/ respiratory rate
• able to respire anaerobically for a long time/ more glycolysis
• haemoglobin may have higher affinity for oxygen