5.2.2 Respiration

Question 1

Where does glycolysis occur in the cell?

Answer 1

• in the cytoplasm

Question 2

Which stages of respiration occur in the mitochondria?

Answer 2

• link reaction
• krebs cycle
• oxidative phosphorylation

Question 3

Is glycolysis an aerobic or anaerobic process?

Answer 3

• anaerobic

- doesn’t need oxygen to take place and it is the first stage

Question 4

Explain the two stages in glycolysis

Answer 4

Stage 1 Phosphorylation:

• glucose is phosphorylated by adding two phosphates from 2 molecules of ATP
• this creates 1 molecule of hexose bisphosphate and 2 molecules of ADP
• then hexose bisphosphate is split up into 2 molecules of triose phosphate

Stage 2 Oxidation:

• triose phosphate is oxidised, forming 2 molecules of pyruvate
• NAD collects the hydrogen ions, forming 2 reduced NAD
• 4 ATP are produced by 4 ADP and 4 inorganic phosphate molecules
• 2 ATP molecules were used in stage one, so there is a net gain of 2 ATP

Question 5

Describe the link reaction

Answer 5

• takes place in the mitochondrial matrix
• pyruvate is decarboxylated: one carbon atom is removed from pyruvate in the form of CO2
• NAD is reduced: it collects hydrogen from pyruvate into acetate
• acetate is combined with coenzyme A to form acetyl coenzyme A
• no ATP is produced in this reaction

Question 6

How many pyruvate molecules are made for every glucose molecule that enter glycolysis

Answer 6

• two pyruvate molecules meaning link reaction and krebs cycle happen twice for every glucose molecule
• two molecules of acetyl CoA go into Krebs cycle
• two molecules of CO2 are released as a waste product of respiration
• two molecules of reduced NAD are formed and go to oxidative phosphorylation

Question 7

Describe the Krebs Cycle

Answer 7

• involves a series of oxidation-reduction reactions
• takes place in the matrix
• acetyl CoA combines with oxaloacetate to form citrate catalysed by citrate synthase
• coenzyme A goes back to the link reaction to be used again
• the 6C citrate molecule is converted to a 5C molecule
• decarboxylation occurs, where CO2 is removed
• dehydrogenation also occurs, where hydrogen is removed
• the hydrogen is used to produced reduced NAD from NAD
• the 5C molecule is then converted to a 4C molecule
• decarboxylation and dehydrogenation occur, producing one molecule of reduced FAD and two reduced NAD
• ATP is produced by the direct transfer of a phosphate group from an intermediate compound to ADP
• when a phosphate group is directly transferred from one molecule to another it’s called substrate-level phosphorylation
• citrate is now converted to oxaloacetate

Question 8

where do 1 CoA, oxaloacetate, 2 CO2, 1ATP, 3 reduced NAD, 1 reduced FAD go after the Krebs cycle

Answer 8

• 1 CoA: reused in the next link reaction
• 2 CO2: released as a waste product
• oxaloacetate: regenerated for use in the next Krebs cycle
• 1 ATP: used for energy
• 3 reduced NAD: to oxidative phosphorylation
• 1 reduced FAD: to oxidative phosphorylation

Question 9

Briefly explain oxidative phosphorylation

Answer 9

• oxidative phosphorylation is the process where energy carried by electrons, from reduced coenzymes (reduced FAD and NAD) is used to make ATP
• oxidative phosphorylation takes place in the inner mitochondrial membrane

Question 10

Fully describe oxidative phosphorylation

Answer 10

• H atoms are released from reduced NAD and reduced FAD as they’re oxidised to NAD and FAD
• the H atoms split into protons (H+) and electrons
• the electrons move along the electron transport chain (made up of three electron carriers), losing energy at each carrier
• the electron transport chain occurs in the inner mitochondrial membrane
• this energy is used by electron carriers to pump protons from the mitochondrial matrix into the inter membrane space
• the concentration of photons is now higher in the inter membrane space then in the mitochondrial matrix, forming an electrochemical gradient
• protons move down the electrochemical gradient, by chemiosmosis, back into the mitochondrial matrix, via ATP synthesis
• this movement drives the synthesis of ATP from ADP and inorganic phosphate
• in the matrix at the end of the electron transport chain, the protons, electrons and O2 (from blood) combine to form water
• oxygen is said to be the final electron acceptor

Question 11

How many ATP molecules can be made from one glucose molecule and why?

Answer 11

• 32 molecules
• glycolysis: 2 ATP produced
• glycolysis: 2 reduced NAD = 2 x 2.5 = 5 ATP molecules
• link reaction (x2): 2 reduced NAD = 2x 2.5
• Krebs cycle (x2): 2 ATP = 2
• Krebs cycle (x2): 6 reduced NAD= 6 x 2.5 = 15
• Krebs cycle: 2 reduced FAD = 2 x 1.5 = 3

= 32

Question 12

Which processes are not used in anaerobic respiration?

Answer 12

• link reaction
• Krebs cycle
• oxidative phosphorylation

Question 13

What are the two types of anaerobic respiration?

Answer 13

• alcoholic fermentation

- lactate fermentation

Question 14

Describe lactate fermentation

Answer 14

• occurs in mammals to produce lactate
• reduced NAD (from glycolysis) transfers hydrogen to pyruvate to form lactate and NAD
• NAD can then be reused in glycolysis

Question 15

Why is glycolysis able to continue without oxygen in anaerobic respiration>

Answer 15

• NAD is regenerated, which glycolysis needs

- so a small amount of ATP is still produced to keep other processes going

Question 16

How much can the body tolerate lactate?

Answer 16

• our cells can tolerate high lactate for short periods of time
• however, too much lactate is toxic and is removed into the bloodstream
• liver takes up lactate from bloodstream and converts it back into glucose in gluconeogenesis

Question 17

Describe alcoholic fermentation

Answer 17

• CO2 is removed from pyruvate to form ethanal using the enzyme pyruvate decarboxylase with coenzyme thiamine diphosphate
• reduced NAD from glycolysis transfers hydrogen to ethanal to form ethanol and NAD
• NAD can then be reused in glycolysis

Question 18

Why does anaerobic respiration release less energy than aerobic respiration?

Answer 18

• anaerobic respiration only include one energy-releasing stage, glycolysis, which only produce 2 ATP per glucose molecule
• other energy-releasing reaction, Krebs and oxidative phosphorylation require oxygen

Question 19

What is a respiratory substrate?

Answer 19

• any biological molecule that can be broken down in respiration to release energy is a respiratory substrate

Question 20

What is the order of energy value in different respiratory substrate?

Answer 20

• lipids: 39.4 kJ/g
• proteins: 17
• carbs: 15.8

Question 21

Why are there different energy values for different respiratory substrate?

Answer 21

• most ATP is made in oxidative phosphorylation, requiring hydrogen atoms from reduced NAD and reduced FAD
• respiratory substrate that contain more H atoms per unit of mass caused more ATP to be produced

Question 22

What is the respiratory quotient and its classifications

Answer 22

• RQ = volume of CO2 released / volume of O2 consumed
• triglycerides: 0.7
• proteins or amino acids: 0.9
• carbs: 1.0

Question 23

Why is the RQ helpful?

Answer 23

• 0.7-1.0 is usual RQ for humans, showing fats and carbs are used
• High RQ, means that organism is short of oxygen, and is respiring anaerobically
• plants may have low RQ because CO2 released in respiration is used for photosynthesis so is not measured

Question 24

Describe a respirometer experiment

Answer 24

• each tube contains potassium hydroxide which absorbs CO2
• control tube has no woodlice
• syringe is used to set fluid to known level
• left for a period of time
• there will be a decrease in the volume of air in test tube due to oxygen consumption by woodlice and CO2 is absorbed
• decrease in volume of air will reduce the pressure in the tube and cause coloured liquid in manometer to move towards test tube
• distance moved by liquid in a given time is measure
• the volume of oxygen can be calculated