Respiration

Question 1

Why do organisms need to respire

Answer 1

Produces ATP currency for:
a) active transport against concentration gradients e.g. to absorb nutrients to small intestine and soil
b) metabolic reactions e.g. to form peptide bonds in protein synthesis
c) muscle contraction
Releases heat for thermoregulation

Question 2

Describe the structure of a mitochondrion

Answer 2

Surrounded by double membrane
Folded inner membrane forms cristae: site of electron transport chain
Fluid matrix: contains mitochondrial DNA, respiratory enzymes, lipids proteins

Question 3

Name the 4 stages of aerobic respiration and where they occur

Answer 3

Glycolysis: Cytoplasm
Link reaction: Mitochondrial matrix
Krebs cycle: Mitochondrial matrix
Oxidative phosphorylation via electron transfer chain: membrane of cristae

Question 4

Outline the stages of glycolysis

Answer 4

Glucose is phosphorylated to hexose bisphosphate
Hexose bisphosphate splits into 2x triose phosphate
2x TP is oxidised to 2x pyruvate
Net gain of 2x reduced NAD and 2x ATP per glucose

Question 5

How does pyruvate from glycolysis enter the mitchondria

Answer 5

Via active transport

Question 6

What happens during the link reaction

Answer 6

1. Oxidation of pyruvate to acetate. Per pyruvate molecule: net gain of 1x CO2 (decarboxylation) and 2H atoms (used to reduce 1x NAD)
2. Acetate combines with Coenzyme A (CoA) to form Acetylecoenzyme A

Question 7

Give a summary reaction for the link equation

Answer 7

Pyruvate + NAD + CoA —> Acetyl CoA + reduced NAD + CO2

Question 8

What happens in the Krebs cycle

Answer 8

Series of REDOX reactions produces:
- ATP by substrate level phosphorylation
- Reduced Coenzymes
- CO2 from decarboxylation
Begins when acetyl group from Acetyle CoA (2C) reacts with oxaloacetate (4C). Cycle regenerates oxaloacetate

Question 9

What is the electron transfer chain (ETC)?

Answer 9

Series of carrier proteins embedded in membrane of the cristae of the mitochondria
Produces ATP through oxidative phosphorylation via chemiosmosis during aerobic respiration

Question 10

What happens in the electron transfer chain

Answer 10

Electrons released from reduced NAD and FAD undergo successive redox reactions
The energy released is coupled to maintaining successive redox reactions
Oxygen acts as final electron acceptor

Question 11

How does chemiosmosis produce ATP during aerobic respiration

Answer 11

Some energy released from the ETC is coupled to active transport of H+ ions (Protons) from mitochondrial matrix into intermembrane space
H+ ions move down concentration gradient into mitochondrial matrix via channel protein ATP synthase

Question 12

State the role of oxygen in aerobic respiration

Answer 12

Final electron acceptor in electron transfer chain
(produces water as a byproduct)

Question 13

Name the stages in respiration that produce ATP by substrate-level phosphorylation

Answer 13

Glycolysis (anaerobic)
Krebs cycle (aerobic)

Question 14

What happens during anaerobic respiration in animals

Answer 14

Only glycolysis continues
Reduced NAD + pyruvate —> oxidised NAD (for further glycolysis) + lactate

Question 15

What happens during anaerobic respirartion in some microorganisms e.g. yeast and some plant cells

Answer 15

Only glycolysis continues, so much less ATP is produced compared to aerobic respiration
Pyruvate is decarboxylated to form ethanol
Ethanal is reduced to ethanol using reduced NAD to produce oxidised NAD for further glycolysis

Question 16

What are the benefits of being able to respire anaerobically

Answer 16

ATP production for vital metabolic processes continues
Production of ethanol / lactate converts reduced NAD back into NAD so glycolysis can continue = maximum yield of ATP in the conditions

Question 17

Suggest how a student could investigate the effect of a named variable on the rate of respiration of a single-celled organism

Answer 17

1. Use respirometer (pressure changes in boiling tube cause a drop of coloured liquid to move)
2. Use a dye as the terminal electron acceptor for the ETC

Question 18

What is the purpose of sodium hydroxide solution in a respirometer set up to measure the rate of anaerobic respiration

Answer 18

Absorbs CO2 so that there is a net decrease in pressure as O2 is consumed

Question 19

How could a student calculate the rate of respiration using a respirometer

Answer 19

Volume of O2 produced or CO2 consumed / time x mass of sample
Volume = distance moved by coloured drop x (0.5 x capillary tube diameter)^2 x Pi

Question 20

Name two types of molecule that can be used as alternative respiratory substrates

Answer 20

Amino acids from proteins
Glycerol and fatty acids from lipids

Question 21

What is the respiratory quotient (RQ)?

Answer 21

RQ = CO2 produced / O2 consumed
Can be used to determine: respiratory substrate being used (carbohydrates: 1.0, lipids: 0.8, proteins: 0.9)
If organism is undergoing anaerobic respiration (anaerobic values are larger)

Question 22

Why do different respiratory substrates have different relative energy values

Answer 22

Depends on the number of hydrogens in the structure which are oxidised to water e.g. the number of hydrogens is greater in fatty acids than carbohydrates