13.4 Respiration

Question 1

What is the word and symbol equation for respiration?

Answer 1

Word: Glucose + Oxygen —> Carbon Dioxide + Water + Energy (ATP)

Question 2

Glucose is not suitable as an immediate energy source in cells; the energy released is used to form ATP which is the immediate energy source. Why is glucose not used DIRECTLY?

Answer 2

• Glucose is broken down in many steps.
• Involves many specific enzymes.
• If glucose is broken down in one step, too much heat energy is released, causing enzymes to denature.

Question 3

The mitochondria in muscles contain many cristae. Explain the advantage of this.

Answer 3

• Larger surface area for electron carrier system/ oxidative phosphorylation;
• Provides more ATP/ energy for (muscle) contraction.

Question 4

What are the two ways ATP can be generated?

Answer 4

• Substrate-level phosphorylation
• Oxidative phosphorylation

Question 5

Explain substrate-level phosphorylation.

Answer 5

ATP is generated directly through energy released via respiration reactions. This occurs in glycolysis and the Krebs Cycle.

Question 6

Explain oxidative phosphorylation.

Answer 6

ATP generated from chemical energy released when reduced hydrogen carrier/co-enzyme (NADH2/FADH2) has been oxidised at the ETC.

Question 7

What are the four main stages in aerobic respiration and where do they take place?

Answer 7

• Glycolysis= cytoplasm/cytosol of cell (SLP)
• Link Reaction= matrix of mitochondria
• Krebs Cycle= matrix of mitochondria (SLP)
• Electron Transport Chain= mitochondrial membranes (OP)

Question 8

What are the end products of glycolysis?

Answer 8

• 2x Pyruvate (3C)
• 2x ATP net
• 2x NADH

Question 9

Explain glycolysis.

Answer 9

1. Phosphorylation of glucose using hydrolysis of ATP.
2. Splits into 2 Triose Phosphate
3. Oxidation of triose phosphate to pyruvate.
4. Net gain of ATP.
5. NAD reduced.

Question 10

Describe how oxidation takes place in glycolysis and in the Krebs cycle.

Answer 10

• removal of hydrogen/dehydrogenation;
• by enzymes/dehydrogenases;
• H accepted by NAD/reduced NAD formed;
• in Krebs cycle, FAD (used as well);

Question 11

What are the end products of the link reaction?

Answer 11

• Acetyl coenzyme A
• CO2
• NADH2
  NO ATP PRODUCED

Question 12

Explain the link reaction.

Answer 12

1. Pyruvate is actively transported into the mitochondrial matrix.
2. Pyruvate is oxidised to acetate and the hydrogen removed (with dehydrogenase) is used to reduce the hydrogen carrier NAD to form reduced NAD/ NADH2.
3. A carbon dioxide molecule is also lost during this reaction (using decarboxylase)
4. A coenzyme A molecule binds to acetate to produce acetyl coenzyme A.
   No ATP is directly produced in the link reaction.

Question 13

Why is acetyl coenzyme A produced?

Answer 13

Coenzyme A is an important molecule that helps bind acetate to the 4C compound in the Krebs Cycles enzyme-controlled reactions.

Question 14

Explain Krebs cycle.

Answer 14

• 2C Acetyl coenzyme A combines with 4C molecule to form 6C compound.
• 6C compound loses CO2 and Hydrogen to convert to a 4C compound.
• NADH, FADH, and 1 ATP produced via substrate-level phosphorylation.
• Cycle can now continue.

Question 15

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

Answer 15

• oxidation of/removal of electrons and H+
• from pyruvate
• acetyl CoA / 6 carbon compound; (credit oxidative decarboxylation)
• substrate level production of ATP / ATP produced in Krebs cycle;
• production of reduced NAD / FAD (allow they take up hydrogen);
• in matrix of mitochondria;
• electrons fed into electron transport chain / used in oxidative
• (Electrons) pass along carriers/through electron transport chain/through series of redox reactions;
• Energy released;
• Protons move into intermembrane space;
• ADP/ADP + Pi;
• ATP synthase;

Question 16

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

Answer 16

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

Question 17

Describe the events of oxidative phosphorylation

Answer 17

• Reduced NAD/FAD oxidised, losing hydrogen;
• Electrons from H atom transferred from coenzyme to coenzyme/carrier to carrier (ETC on cristae of inner membrane)
• Energy released (from electrons) through series of redox reactions;
• Energy released used to pump H+/ protons into intermembrane space;
• H+/ protons flow back through ATP synthase to produce ATP from ADP and phosphate.
• Electrons and H+ recombine with O2 to form water;
• Oxygen is the final electron acceptor.

Question 18

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

Answer 18

• Equilibrium reached;
• Allow for expansion/pressure change in apparatus;
• Allow respiration rate of seeds to stabilise;

Question 19

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

Answer 19

• Large range/difference/increase in numbers;
• Accept reference to exponential (increase)

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/ No NADH
  OR
• Fewer/ No hydrogens/electrons removed and passed through ETC.
• Oxygen is the final electron acceptor.

Question 22

How to respirometers work as the plant or animal respires?

Answer 22

1. Oxygen is used for aerobic respiration.
2. Reduces the volume of oxygen in the chamber, reducing pressure.
3. Solution of potassium hydroxide absorbs CO2 released by plant or animal.
4. Ink in connecting tube moves from higher to lower pressure along graduated scale.
5. Measure time taken.

Question 23

If respiration is aerobic in a plant or animal or bacteria…

Answer 23

WITH CO2 ABSORBER…
- CO2 absorbed
- Decrease in pressure
- Liquid moves TOWARDS organism.

WITHOUT CO2 ABSORBER…
- Equilibrium
- No Movement

Question 24

If respiration is anaerobic in plants or yeast or bacteria…

Answer 24

WITH CO2 ABSORBER…
- No O2 in
- CO2 absorbed
- Equilibrium
- No movement

WITHOUT CO2 ABSORBER…
- No oxygen used
- No CO2 absorbed
- Pressure increase
- Liquid moves AWAY from organism.

Question 25

If respiration is anaerobic in animals...

Answer 25

WITH CO2 ABSORBER... - No CO2 absorbed - No O2 uptake. - Equillibrium - No movement WITHOUT CO2 ABSORBER... - Equilibrium - No movement.

Question 26

Products of anaerobic respiration in animals

Answer 26

Lactate (Lactic acid) PYRUVATE REDUCED TO LACTATE

Question 27

Products of anaerobic respiration in plants and yeast.

Answer 27

Ethanol and CO2 PYRUVATE REDUCED INTO ETHANOL AND CO2

Question 28

How can glycerol and fatty acids be used as alternative respiratory substrates?

Answer 28

- Lipids hydrolysed into glycerol and fatty acids. - Glycerol phosphorylated and converted to TP - Fatty acids break down into 2C components, converted into Acetyl coenzyme A. - Oxidation of fatty acids yields many H atoms to reduce NAD and FAD to be used as part of oxidative phosphorylation of ATP

Question 29

How can proteins be used as an alternative respiratory substance?

Answer 29

- Proteins hydrolysed into amino acids - Amino groups removed (deamination) - Remaining CH(R)COOH group will enter respiration at different stages depending on how many C atoms. --> 3C into pyruvate (glycolysis/ link reaction) --> 4C and 5C into Krebs cycle intermediates

Question 30

What happens if oxygen does not remove H+ and electrons in ETC?

Answer 30

- Would be a ‘back up’ of electrons along the ETC - Process of respiration (in the mitochondria) will come to a halt.