Ch 12 Energy and respiration

Question 1

What adenosine triphosphate?

Answer 1

• ATP
• a nucleotide derivative
• consists of ribose, adenine and three phosphate groups

Question 2

Why do we need ATP (energy)?

Answer 2

● Anabolic reactions e.g. synthesis of DNA and
proteins
● Active transport
● Movement
● Homeostasis

Question 3

Why is ATP used for energy?

Answer 3

● ATP is tri-phosphorylated. The removal of each
phosphate releases energy.
● ATP is easily hydrolysed and water-soluble (easy
to transport), making it a useful source of energy.

Question 4

Name the four main stages of aerobic respiration

and state where they occur.

Answer 4

● Glycolysis - cytosol
● Link reaction - mitochondrial matrix
● Krebs cycle - mitochondrial matrix
● Electron transport chain - inner mitochondrial
membrane

Question 5

Outline the stages of glycolysis.

Answer 5

1. Glucose (hexose sugar) phosphorylated to hexose
   bisphosphate by 2× ATP
2. Hexose bisphosphate splits into 2× triose phosphate (TP)
3. 2 molecules of TP oxidised to 2× pyruvate
   Net gain of 2× reduced NAD (NADH) and 2× ATP per glucose.

Question 6

How does pyruvate from glycolysis enter the

mitochondria?

Answer 6

Via active transport (oxygen is required)

Question 7

What happens during the link reaction?

Answer 7

1. Oxidative decarboxylation and dehydrogenation of
   pyruvate to form acetate
   Net gain of CO2 and 2× reduced NAD
2. Acetate combines with coenzyme A (CoA) to form
   acetyl coenzyme A

Question 8

Define “substrate level phosphorylation”.

Answer 8

The synthesis of ATP by the transfer of a
phosphate group from a phosphorylated
intermediate to ADP.

Question 9

What happens in the Krebs cycle?

Answer 9

Series of redox reactions that produces:
● ATP by substrate-level phosphorylation
● Reduced coenzymes
● CO2 from decarboxylation
Begins when the acetyl group from Acetyl CoA (2C) reacts
with oxaloacetate (4C).The cycle regenerates oxaloacetate.

Question 10

What is the electron transfer chain (ETC)?

Answer 10

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

Question 11

What happens in the electron transfer chain (ETC)?

Answer 11

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

Question 12

How does chemiosmosis produce ATP during

aerobic respiration?

Answer 12

Some energy released from the ETC is coupled to the active transport of H+
ions (protons) from the mitochondrial matrix into the intermembrane space.
H+ ions move down their concentration gradient into the mitochondrial matrix
via the channel protein ATP synthase.
ATP synthase catalyses ADP + Pi → ATP
Note: chemiosmosis also occurs in photosynthesis in chloroplasts.

Question 13

State the role of oxygen in the electron transfer

chain.

Answer 13

Final electron acceptor:

O2 + 4H+ + 4e- → 2H2O

Question 14

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

Answer 14

● Glycolysis (anaerobic)

● Krebs cycle (aerobic)

Question 15

What is the respiratory quotient? Write

the equation.

Answer 15

Ratio of CO2 produced to O2 consumed.

RQ = CO2/O2

Question 16

What is the RQ of carbohydrates, lipids

and proteins?

Answer 16

● Carbohydrates: 1
● Lipids: 0.7-0.72
● Proteins: 0.8-0.9

Question 17

What could an RQ of greater than 1 indicate?

Answer 17

● May indicate the conversion of
carbohydrates to lipids
● RQ in anaerobic respiration is ∞

Question 18

Why do different respiratory substrates have

different relative energy values?

Answer 18

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.

Question 19

Outline anaerobic respiration in muscle cells.

Answer 19

● Only glycolysis continues
● Reduced NAD (product of glycolysis) transfers
the H to pyruvate, forming lactic acid and
regenerating NAD
● Catalysed by enzyme lactate dehydrogenase

Question 20

Outline anaerobic respiration in plants and

microorganisms.

Answer 20

● Only glycolysis continues
● Pyruvate is decarboxylated to form ethanal
● Ethanal accepts a H from reduced NAD making ethanol. NAD
regenerated for glycolysis
● Less ATP is produced than in aerobic respiration

Question 21

Name two types of molecule that can be used as

alternative respiratory substrates.

Answer 21

● (amino acids from) proteins

● (glycerol and fatty acids from) lipids

Question 22

Compare the efficiency of aerobic and anaerobic

respiration

Answer 22

Hydrolysis of 1 mole glucose produces 2880 kJ. 1 molecule ATP produces
30.6 kJ. In aerobic respiration 32 ATP are gained whereas in anaerobic 2
ATP are gained.
● Aerobic efficiency= [(32 × 30.6)/2800] × 100 = 34%
● Anaerobic efficiency= [(2 × 30.6)/2800] × 100 = 2.1%
● Aerobic respiration is = 34/2.1= 16.2× more efficient than anaerobic

Question 23

Define oxygen debt and oxygen deficit.

Answer 23

● Oxygen debt (also referred to as Excess Post-Exercise
Oxygen Consumption or EPOC) is the amount of additional
O2 needed after exercise to return body systems to their
previous state
● Oxygen deficit is the volume of O2 required during exercise
minus volume of O2 obtained

Question 24

How is rice adapted for growth in a low oxygen

environment?

Answer 24

● Rapid growth maintains flowering parts above water line allowing gas
exchange through the leaves
● Aerenchyma in stem allows gases to move to submerged parts of the
plant
● Hydrophobic coating on leaves maintains air film around plant
● Root cells produce alcohol dehydrogenase to offset ethanol toxicity from
anaerobic respiration

Question 25

How can DCPIP be used to measure respiration in

yeast?

Answer 25

To establish the chemiosmotic gradient, H+ is pumped
out of the matrix. H+ reduces DCPIP producing a
colour change from blue to colourless. The rate at
which this change takes place allows us to measure
the rate of respiration in yeast.

Question 26

Define the term “respirometer”.

Answer 26

A device used to determine respiration
rate in living organisms by measuring the
change in volume of oxygen or carbon
dioxide.

Question 27

How could a student calculate the rate of respiration

using a respirometer?

Answer 27

volume of O2 produced or CO2 consumed/ time ×
mass of sample
volume = distance moved by coloured drop ×
(0.5 × capillary tube diameter)2 × π