Respiration PPQs

Question 1

Describe how acetyle coA is formed in the link reaction (2)

Answer 1

• pyruvate is oxidised to acetate and carbon dioxide is released
• acetate combines with CoA

Question 2

Explain how oxaloacetate binding to citrate synthase enables acetyl CoA to then bind to citrate synthase (2)

Answer 2

• changes tertiary structure and hence active site

- making it complimentary to the substrate

Question 3

X has a similar shape to acetyl CoA. Suggest how production of x could control the rate of the reaction (2)

Answer 3

• x is a competitive inhibitor so it binds to the active site of the enzyme
• preventing and E-S complex forming

Question 4

Why does converting pyruvate to lactate allow the continued production of ATP during anaerobic respiration (2)

Answer 4

• it regenerates NAD

- which is used in glycolysis

Question 5

In muscles, some lactate is converted back to pyruvate when they are well supplied with oxygen. Why is this an advantage? (1)

Answer 5

build up of lactic acid is toxic

Question 6

RQ value for aerobic respiration of glucose and why?

Answer 6

1

volume of CO2 produce = volume of O2 used up

Question 7

RQ equation

Answer 7

vol. CO2 produced/ vol. O2 used up

Question 8

Suggest why the rate of carbon dioxide release (spiracles opening) in insects increases as temperature increases. (3)

Answer 8

• higher temperatures means more enzyme activity
• respiration rate increases so CO2 production increases
• so needs to be released at a faster rate and spiracles must open more often

Question 9

Why is a layer of oil used in an anaerobic respiration experiment? (1)

Answer 9

= prevents oxygen being taken up

Question 10

Explain why the conversion of pyruvate to lactate allows for glycolysis to occur. (2)

Answer 10

• when pyruvate is converted to lactate it regenerates NAD

- which can be use din glycolysis (to form reduced NAD)

Question 11

Aerobic respiration produces more ATP per glucose molecule than anaerobic respiration. Explain why. (2)

Answer 11

aerobic has Krebs cycle and oxidative phosphorylation

anaerobic only has glycolysis

Question 12

People with mitochondrial disease have dysfunctioning mitochondria.

Why can people with mitochondrial disease only exercise for a short amount of time?

Answer 12

• the dysfunctioning mitochondria mean less aerobic respiration
• so less ATP produced for muscle contraction

Question 13

ice cold

isotonic

Answer 13

reduce enzyme activity

prevent osmosis and cell from bursting/shrinking

Question 14

Explain the constant (no gradient) line between P and Q

Answer 14

oxygen concentration is constant because

• no aerobic respiration
• because no substrate to respire

Question 15

Explain the line between Q and R (steady negative gradient)

Answer 15

• aerobic respiration uses oxygen (so it is taken up)

- as terminal electron acceptor

Question 16

When the mitochondria are isolated, what need sto be added to the solution for aerobic respiration to occur? (3)

Answer 16

• ADP
• Pi
• Respiratory substrates

Question 17

Explain why, after cyanide is added to solution, oxygen concentration continues to decrease at a slower rate in plant mitochondria?

Answer 17

• oxygen conc. continues to fall in plant mitochondria because they continue to aerobically respire
• because oxidative phosphorylation continues in plant mitochondria
• because plant mitochondria cytochrome oxidase is more resistant to cyanide (than animal mitochondria which when cyanide is added immediately stop aerobically respiring because the cyanide screws up the ETC)

Question 18

What number carbon compound enters the Krebs cycle and what does it join with?

Answer 18

2 carbon acetyl CoA combines with 4C oxaloacetate to form 6C citrate

Question 19

Where does th elink reaction occur (what travels in) ?

Answer 19

pyruvate passes through mitochondrial membrane and then combines with CoA to form acetyl CoA (in the process reduced NAD and CO2 formed)

Question 20

Explain why oxygen is needed for the production of ATP on the cristae of the mitochondrion. (3)

Answer 20

• ATP formed as electrons are passed along the ETC
• oxygen is the final acceptor of these electrons
• where they then combine with protons and oxygen to form water at the end of the chain

Question 21

Describe the part played by the inner membrane of a mitochondrion in producing ATP. (3)

Answer 21

• electrons pass down ETC
• provides energy for active transport of protons into the intermembral space
• protons then flow back into matrix through ATP synthase
• this energy is used to combine ADP and Pi

Question 22

Explain why the scientist did not use glucose as the respiratory substrate. (2)

Answer 22

• glucose broken down during glycolysis in the cytoplasm

- (this cannot happen bc mitochondria are isolated) - so glucose cannot cross the mitochondrial membrane

Question 23

Explain how malonate inhibits the formation of fumarate from succinate. (2)

Answer 23

• competitive inhibitor

- prevents E-S complex forming

Question 24

The scientist measured the uptake of oxygen by the mitochondria during the investigation. The uptake of oxygen decreased when malonate was added. Explain why. (2)

Answer 24

• Krebs inhibited as coenzymes not reduced

- H not passed to the ETC so oxygen not used as much as terminal electron acceptor

Question 25

Apart from respiration, give three uses of ATP in a liver cell. (3)

Answer 25

• mitosis
• bile production
• DNA synthesis

Question 26

Human skeletal muscle can respire both aerobically and anaerobically. Describe what happens to pyruvate in anaerobic conditions and explain why anaerobic respiration is advantageous to human skeletal muscle.(4)

Answer 26

• pyruvate converted to lactate
• NADH oxidised to NAD (regeneration of NAD) and also production of CO2
• allows glycolysis to continue
• so ATP production present even when no oxygen present

Question 27

Humans synthesise more than their body mass of ATP each day. Explain why it is necessary for them to synthesise such a large amount of ATP. (2)

Answer 27

• ATP cannot be stored

- ATP only releases a small amount of energy at a time