Respiration

Question 1

Why do organisms need to respire?

Answer 1

● Produces ATP as energy currency for:
a) active transport against concentration gradients e.g.
to absorb nutrients from small intestine/soil.
b) metabolic reactions e.g. to form peptide bonds in
protein synthesis.
c) muscle contraction.
● Releases heat energy 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 main stages in 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

1. Glucose is phosphorylated to hexose bisphosphate by 2x ATP.
2. Hexose bisphosphate splits into 2x triose phosphate (TP).
3. 2x TP is oxidised to 2x pyruvate.
   Net gain of 2x reduced NAD & 2x ATP per glucose.

Question 5

Draw a flowchart to represent what happens during glycolysis.

Answer 5

IMAGE 42

Question 6

How does pyruvate from glycolysis enter the mitochondria?

Answer 6

via active transport

Question 7

What happens during the link reaction?

Answer 7

1. Oxidation of pyruvate to acetate.
   per pyruvate molecule: net gain of 1xCO2 (decarboxylation) & 2H atoms (used to reduce 1xNAD).
2. Acetate combines with coenzyme A (CoA) to form Acetylcoenzyme A.

Question 8

Give a summary equation for the link reaction.

Answer 8

pyruvate + NAD + CoA
→
Acetyl CoA + reduced NAD + CO2

Question 9

What happens in the Krebs cycle?

Answer 9

series of redox reactions produces:
● ATP by substrate-level phosphorylation
● reduced coenzymes
● CO2 from decarboxylation
Begins when acetyl group from Acetyl CoA (2C) reacts with oxaloacetate (4C). Cycle regenerates oxaloacetate.

Question 10

Outline the stages of the Krebs cycle.

Answer 10

IMAGE 43

Question 11

What is the electron transfer chain (ETC)?

Answer 11

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

Question 12

What happens in the electron transfer chain (ETC)?

Answer 12

Electrons released from reduced NAD & FAD undergo successive redox reactions.
The energy released is coupled to maintaining proton gradient or released as heat.
Oxygen acts as final electron acceptor.

Question 13

How does chemiosmosis produce ATP during aerobic respiration?

Answer 13

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.
ATP synthase catalyses ADP + Pi → ATP

Question 14

State the role of oxygen in aerobic respiration.

Answer 14

Final electron acceptor in electron transfer chain.

produces water as a byproduct

Question 15

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

Answer 15

● glycolysis (anaerobic) ● Krebs cycle (aerobic)

Question 16

What happens during anaerobic respiration in animals?

Answer 16

IMAGE 44

Question 17

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

Answer 17

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

Question 18

Draw a flowchart to show how ethanol is produced during anaerobic respiration.

Answer 18

IMAGE 45

Question 19

What are the benefits of being able to respire anaerobically?

Answer 19

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 20

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

Answer 20

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 21

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

Answer 21

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

Question 22

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

Answer 22

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 π.

Question 23

Name 2 types of molecule that can be used as alternative respiratory substrates.

Answer 23

● (amino acids from) proteins

● (glycerol and fatty acids from) lipids

Question 24

What is the respiratory quotient (RQ)?

Answer 24

RQ = carbon dioxide produced / oxygen 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 25

Why do different respiratory substrates have different relative energy values?

Answer 25

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.