Respiration

Question 1

Respiration Equation

Answer 1

Glucose + Oxygen -> Carbon Dioxide + Water + Energy

Question 2

Why is glucose NOT used directly?

Answer 2

• glucose broken down in many steps. involving many specific enzymes
  if glucose is broken down in one step:
• too much heat energy released causing enzymes to denature

Question 3

How is mitochondria adapted to its function?

Answer 3

• Small organelle= large SA/vol ratio
• Short diffusion path for O2
• many cristae increase SA for ETC/ ATP synthase
• aqueous matrix (soluble enzymes)

Question 4

Explain advantage of many cristae

Answer 4

• larger SA for electron carrier system
• provides more ATP for muscle contraction

Question 5

What are the 4 stages of aerobic respiration?

Answer 5

1. glycolysis (cytoplasm)
2. link reaction (matrix of mitochondria)
3. krebs cycle (matrix of mitochondria)
4. electron transport chain (inner mitochondrial membranes)

Question 6

Two ways that ATP can be generated

Answer 6

• Substrate-level phosphorylation- ATP generated directly through energy released via respiration reactions. This occurs in Glycolysis and the Krebs cycle
• Oxidative phosphorylation – ATP generated from the chemical energy released when a reduced hydrogen carrier or coenzyme (NADH2 or FADH2) has been oxidised at the Electron Transfer Chain.

Question 7

Glycolysis

Answer 7

• Glucose (6C) activated by phosphorylation requires hydrolysis of 2 ATP to 2ADP to provide 2 phosphates
• Glucose phosphate then splits into 2 x triose phosphate
• TP (3C) oxidised to pyruvate (3C) and involves loss of H (via dehydrogenase enzyme) reduces hydrogen carrier NAD to NADH2
• ATP produced via substrate level phosphorylation

Produces:
2 net ATP
2 NADH
2 pyruvate ( leave mitochondria by AT)

Question 8

The Link reaction

Answer 8

• Pyruvate is oxidised to acetate
• Hydrogen removed to form reduced NAD
• CO2 is lost via decarboxylation
• NO ATP is produced
• Acetyl co A produced

Question 9

The Krebs cycle

Answer 9

• 2C Acetyl co A combines with 4C molecule to form 6C compound
• 6C compound loses CO2 and Hydrogen to convert to a 4C compound and 1x ATP (via substrate-level phosphorylation)
• The cycle can now continue.

Question 10

Describe how oxidation takes place in glycolysis/ krebs?

Answer 10

1. removal of H+
2. by enzymes
3. H accepted by NAD
4. in krebs cycle FAD used

Question 11

The Electron Transport Chain (ETC)

Answer 11

1.The reduced H carriers are oxidised losing Hydrogen.
2. The electrons pass down a series of electron carriers in a series of REDOX reactions.
3. As the electrons pass along the electron transport chain they lose energy, some of which is used to pump the H+ through the inner mitochondrial membrane into intermembrane space
4. Some of the energy is also lost as heat.
5. The H+ pass diffuse, down a proton gradient, into the matrix via ATP synthase enzymes and enough energy is provided to form ATP.
6. The electrons and H+ recombine with Oxygen gas to form water.
7. Oxygen is the final/terminal electron acceptor.
8. Without oxygen removing H+ and electrons, there would be a ‘back up’ of electrons along the ETC and the process of cellular respiration will come to a halt

Question 12

Water is a waste product of aerobic respiration. Describe how water is formed at the end of aerobic respiration.

Answer 12

• oxygen is terminal/final electron acceptor;
• combines with electrons and protons (to form water);

Question 13

Describe the roles of the coenzymes and carrier proteins in the synthesis of ATP.

Answer 13

*reduced NAD
* electrons transferred from coenzyme to coenzyme
* energy released as electrons passed on
* energy used to synthesise ATP from ADP and Pi
* H+ / protons pumped into inter membrane space;
* H+ / protons diffuse back through ATP synthase enzyme;

Question 14

Describe how ATP is made in mitochondria.

Answer 14

• Substrate level phosphorylation
• link reaction produces reduced NAD
• Electrons released from reduced NAD
• (Electrons) pass along carriers
• Energy released
• Protons pumped into inter membrane space;
• ADP/ADP + Pi
• ATP synthase;

Question 15

Describe the events of oxidative phosphorylation

Answer 15

• NAD/FAD reduced
• ETC on cristae
• electrons transferred from coenzyme to coenzyme
• energy released as electrons passed on
• protons pumped into intermembrane space
• protons flow back through enzyme
• energy used to synthesise ATP from ADP and phosphate

Question 16

Anaerobic respiration

Answer 16

The Link reaction, Krebs cycle and electron transport chain stop as there is no Oxygen to act as the Final / terminal electron acceptor.

Glycolysis does not require Oxygen and can continue in the absence of Oxygen, however, for glycolysis to continue NAD must be regenerated.

The H from the reduced NAD in glycolysis is now accepted by pyruvate rather than passing through the electron transport chain.

The pyruvate is reduced to lactate in animals and ethanol & CO2 in plants.

Question 17

Respirometer expected results

Answer 17

Question 18

Explain how the amount of ATP is increased by reactions occurring inside a mitochondrion

Answer 18

• oxidation of H+
• from pyruvate
• ATP produced in Krebs cycle;
• production of reduced NAD / FAD
• in matrix of mitochondria
• electrons fed into electron transport chain
• phosphorylation on cristae
• linked to ATP production
• ATP synthase

Question 19

Give two reasons why the respirometer was left for 10 minutes when it was first placed in the water bath.

Answer 19

1. Equilibrium reached;
2. Allow for expansion/pressure change in apparatus;

Question 20

Explain why converting pyruvate to lactate allows the continued production of ATP by anaerobic respiration.

Answer 20

• Regenerates NAD /
  Oxidises reduced NAD;
• (So) glycolysis continues;

Question 21

Malonate inhibits a reaction in the Krebs cycle.
Explain why malonate would decrease the uptake of oxygen in a respiring cell.

Answer 21

• Less reduced NAD
• Oxygen is the final electron acceptor;

Question 22

In many mammals, ‘uncoupling proteins’ help to maintain a constant body temperature during hibernation.

Suggest and explain how.

Answer 22

1. Allow passage of protons/H+;
2. (Energy) released as heat

Question 23

Explain why a log scale is used to record the number of cells/bacteria.

Answer 23

Large range/difference/increase in numbers (of cells/bacteria);
Accept reference to exponential (increase)