Chapter 12: Respiration

Question 1

Explain why anaerobic respiration produces less ATP than in aerobic respiration.

Answer 1

Only glycolysis occurs = net gain of 2 ATP from substrate-linked phosphorylation

No final hydrogen acceptor = ETC stops functioning = no chemiosmosis where most ATP would be produced

Question 2

Describe the structure of mitochondria and how it relates to its function.

Answer 2

Outer membrane
- Presence of carriers
Intermembrane
- High concentration of protons
- Protons move from intermembrane to matrix

Inner membrane
- Folded therefore larger SA
- Has ATP synthase, ETC, carrier proteins

Matrix
- Enzymes, site of Link reaction and Krebs

Question 3

Describe respiration in anaerobic conditions in mammalian liver cells and describe how this differs from yeast cells.

Answer 3

Only glycolysis occurs = pyruvate cannot enter mitochondrion

Pyruvate is reduced by reduced NAD forming lactate catalysed by lactate dehydrogenase

Produces 2 ATP AND allows glycolysis to continue

Yeast cells has decarboxylation producing ethanal, so 2 steps

Ethanal is reduced by reduced NAD forming ethanol catalysed by ethanol dehydrogenase

Question 4

Describe the differences of chemiosmosis at mitochondria and chloroplasts.

Answer 4

Chemiosmosis @ mitochondria
- Oxidative phosphorylation
- Inner mitochondrial membrane
- Reduced NAD provides electrons
- H+ into intermembrane space
- Oxygen final electron acceptor

Chemiosmosis @ chloroplasts
- Photophosphorylation
- Thylakoid membrane
- Photolysis provides electrons
- H+ into thylakoid
- NADP final electron acceptor

Question 5

Explain why ATP is needed in the first stage of glucose.

Answer 5

Activates glucose to make it more reactive

Question 6

Suggest 2 reasons why actual net number of ATP produced is less than the theoretical number.

Answer 6

ATP used to transport pyruvate into mitochondrial matrix

Some protons leak from intermembrane space

Some energy lost as heat

Glucose not completely broken down

Question 7

Outline the roles of NAD and FAD in aerobic respiration.

Answer 7

Transport hydrogen to the inner mitochondrial membrane = acts as coenzyme for dehydrogenation.

Reduced during glycolysis, link reaction and Krebs cycle

Question 8

Explain how ATP is formed during oxidative phosphorylation.

Answer 8

Reduced NAD and FAD releases hydrogen at inner membrane.

Hydrogen splits into protons and electrons. Electrons pass along ETC, releasing energy used to pump protons into intermembrane space.

High concentration of protons in intermembrane space, so steep proton gradient is achieved.

Protons diffuse back into matrix through ATP synthase which triggers chemiosmosis. ATP produced from ADP and Pi.

Question 9

Describe how a molecule of glucose is converted to pyruvate and then to acetyl CoA.

Answer 9

Glycolysis occurs first. Glucose is phosphorylated by ATP to fructose bisphosphate.

Fructose bisphoshphate splits to form 2 TP, which is oxidised so producing reduced NADH.

2 ATP is produced due to substrate-linked phosphorylation.

Pyruvate enters mitochondrial matrix, undergoes link reaction where pyruvate is decarboxylated and dehydrogenated, then combines with coenzyme A to form acetyl CoA.

Question 10

Outline oxidative phosphorylation.

Answer 10

Reduced NAD and FAD releases hydrogen which splits into proton and electron at inner mitochondrial membrane.

Electrons pass through ETC, releasing energy that is used to actively pump protons into intermembrane space, establishing proton gradient.

Protons diffuse through ATP synthase, ATP produced from ADP and Pi from chemiosmosis.

Oxygen acts as final electron acceptor to form water.

Question 11

Define the term respiratory quotient (RQ).

Answer 11

Volume of carbon dioxide produced/volume of oxygen consumed per unit time.

Question 12

Explain how rice is adapted to grow with its roots submerged in water.

Answer 12

Rice plants has aerenchyma which allows gases to diffuse through aerenchyma down to roots, allowing for aerobic respiration.

Some leaves trap air underwater due to ridges on leaves.

Alcohol fermentation occurs under anaerobic conditions, and root cells can tolerate ethanol as ethanol dehydrogenase is present to break down ethanol.

Question 13

Name the waste products excrete during anaerobic respiration and describe what occurs to these products to help return to normal level.

Answer 13

Lactate produced will be taken to liver and converted to pyruvate which is converted to glucose.

Carbon dioxide produced is detected by pH receptors, therefore increased breathing rate so carbon dioxide goes into alveoli.

Question 14

Describe how ATP is made by substrate-linked reactions.

Answer 14

Inorganic phosphate, Pi added to ADP resulting in phosphorylated compound.

Question 15

State the role of acetyl coenzyme A in respiration.

Answer 15

Carrier of acetyl group to the Krebs cycle.

Question 16

Explain the use of extra oxygen with rapid breathing after exercising.

Answer 16

Oxygen debt occurs.

Extra oxygen is needed to convert lactate to pyruvate in liver cells to reoxygenate haemoglobin.

Question 17

Explain what happens to reduced NAD from glycolysis and link reaction

Answer 17

Reduced NAD will move into mitochondrial matrix carrying hydrogen atom.

Reduced NAD will donate hydrogen atom at inner membrane.

Question 18

State the specific role of oxygen in the mitochondrion.

Answer 18

Final electron and proton acceptor in ETC.

Question 19

Explain specifically role of inner mitochondrial membrane in chemiosmosis.

Answer 19

Site of ETC, so energy is provided so protons are pumped into intermembrane space = creating electrochemical gradient.

Inner membrane is also impermeable to protons, so electrochemical gradient is maintained.

Protons diffuse back into matrix through ATP synthase, where chemiosmosis occurs.

ADP + Pi –> ATP, also known as oxidative phosphorylation.

Question 20

Explain why lipids have higher energy value than carbohydrates.

Answer 20

Lipids have more C-H bonds = produces more reduced NAD = more hydrogen atoms used to create proton gradient = more oxidative phosphorylation = more ATP per unit mass.

So, RQ is lower because need more oxygen to breakdown the molecule.

Question 21

Suggest why it is difficult to compare ability of 3 types of cells to respire aerobically, based only on the mean number of mitochondria per cell.

Answer 21

Mitochondria varying in size.

Question 22

What is the role of the ETC in inner membrane?

Answer 22

Splits H into electrons and protons.

As electron goes along ETC, it provides energy.

Energy is used to pump protons into intermembrane space.

Question 23

State how glucose and oxygen requirements of cancer cells differ from normal cells.

Answer 23

Cancer cells uses more glucose and less oxygen.

So, little ATP, net gain of 2 from glycolysis is already sufficient.

Question 24

Describe how you would carry out an investigation to determine RQ of germinating barley seeds.

Answer 24

Use respirometer.

Insert seeds on gauze, and sodalime to absorb carbon dioxide in test tube.

Then, attach manometer. Movement of fluid in manometer shows oxygen uptake.

Measure oxygen uptake after certain time. Then, repeat experiment without sodalime.

Difference in manometer readings is due to CO2 given out.

Question 25

Outline the main stages of link reaction and Krebs cycle.

Answer 25

Link reaction:

Pyruvate enters mitochondrial matrix, then decarboxylated and dehydrogenated (Link reaction).

Acetyl group is formed, which combines with coenzyme A to form acetyl CoA.

Krebs cycle:

Acetyl CoA enters Krebs cycle, combining with oxaloacetate forming citrate.

Citrate is decarboxylated and dehydrogenated, hydrogen atoms accepted by NAD and FAD. ATP is made by substrate-linked phosphorylation.

Oxaloacetate is regenerated.

Question 26

Explain why less ATP is produced when yeast respires in anaerobic conditions compared to when yeast respires in aerobic conditions.

Answer 26

Less ATP because only glycolysis occurs = only net 2 ATP produced. No oxygen as final electron acceptor, so pyruvate does not enter mitochondria.

Oxidative phosphorylation does not occur, when this stage is producing most ATP.

Pyruvate is converted to ethanol, which is still energy-rich.

Question 27

Describe how you would investigate, using a simple respirometer, to measure effect of temperature on respiration rate of insect larvae.

Answer 27

Use respirometer.

Place larvae on gauze, place sodalime to absorb carbon dioxide.

Use water bath to set water in beaker in temperature of 20, 25, 30, 35 degrees celsius.

Mark initial position of liquid in manometer, then leave for 15 minutes.

Measure distance liquid moved, then calculate rate = distance/time.

Use tap to reset respirometer, and repeat 3 times then calculate average values of distance moved per unit time.

Plot graph of rate v temperature.

Question 28

Describe how you would investigate effect of temperature on rate of respiration of yeast in anaerobic conditions using redox indicator such as mathylene blue.

Answer 28

Use DCPIP as hydrogen acceptor = colourless when reduced.

Put yeast suspension and DCPIP in tube. Put thin layer of oil to prevent oxygen reaching yeast, so anaerobic respiration occurs.

Measure how long it takes for DCPIP to go colourless by using colorimeter. Repeat twice and use average value.

Repeat experiment with 4 different temperatures, use water bath to adjust.

Plot graph respiration rate against temperature.

Question 29

Suggest why molecules allowing protons transported across inner mitochondrial membrane, back into the matrix reduces aerobic respiration.

Answer 29

Protons diffuse through molecule into matrix, so less protons pass through ATP synthase, so less ATP produced.

Question 29

Outline glycolysis.

Answer 29

Phosphorylation:
Glucose phosphorylated by 2 ATP to form fructose bisphosphate.

Lysis:
Fructose bisphosphate splits into 2 molecules of triose phosphate, TP.

Oxidation:
Hydrogen removed from TP, transferred to coenzyme NAD to form 2 reduced NAD per TP.

Dephosphorylation:
Phosphates transferred from intermediate substrate moelcules to form 4 ATP through substrate-linked phosphorylation.

Pyruvate produced.

Question 30

State 2 examples of anabolic reactions.

Answer 30

Anabolic reactions uses energy, and synthesise something large from something smaller units.

Examples:

To make proteins, lipids, carbohydrates.

Phosphorylation.

DNA replication.

Question 31

Function of ATP in glycolysis.

Answer 31

Phosphorylates glucose to fructose bisphosphate.

So, glucose is activated and cannot leave the cell.

Answer 32

Energy from ETC is released as heat.

Energy not used to join ADP and Pi during chemiosmosis also released as heat.

Question 33

Compare and contrast anaerobic respiration in mammalian tissues and yeast cells.

Answer 33

Both:
- Occur in cytoplasm
- Only involves glycolysis
- Makes 2 net ATP
- Aims to keep regenerating NAD from NADH

Differences:

What is reduced?
M: Pyruvate
Y: Ethanal

What is end product?
M: Lactic acid
Y: Ethanol

Got carboxylation?
M: No
Y: Yes

How many steps?
M: 1
Y: 2

Enzyme?
M: Lactate dehydrogenase
Y: Ethanol dehydrogenase

Process?
M: Reversible
Y: Irreversible

Question 34

Outline 2 examples of movement in cells uses ATP.

Answer 34

Active transport of protons.
Sarcomere contraction.
Exocytosis of ACh.
Endocytosis/Phagocytosis.
Chromosome movement during mitosis.
Flagella beating.

Question 35

Suggest 2 reasons why actual net number of ATP molecules synthesised is less than theoretical number.

Answer 35

ATP used to:
i) Transport pyruvate into mitochondrial matrix.
ii) Some protons leak from intermembrane space into matrix.
iii) Some energy from ETC lost as heat.
iv) Glucose not completely broken down.

Question 36

Describe properties of ATP suitable for its role as universal energy currency.

Answer 36

Water soluble, so easily transported across cell.

ATP loses phosphate, hydrolysed by ATPase to release energy just enough not to be wasteful.

Can be regenerated.

Question 37

Suggest why ATP is needed for protein synthesis.

Answer 37

i) Unwinding DNA
ii) Activating RNA nucleotides
iii) Joining of amino acids together
iv) mRNA synthesis
v) Movement of mRNA from nucleus.
vi) Post-translation modification at golgi.