Module 5.6 - Respiration

Question 1

What are the 4 stages in aerobic respiration?

Answer 1

1) Glycolysis
2) The Link reaction
3) The Krebs cycle
4) Oxidative photophosphorylation.

Question 2

All cells use glucose to respire but give some examples of other organic molecules organisms can break down to respire?

Answer 2

E.g. Fatty acids, amino acids.

Question 3

Describe the structure of a mitochondrion?

Answer 3

Has an outer mitochondrial membrane and an inner mitochondrial membrane. It then has folds inside called crista (or plural cristae) which has mitochondrial DNA in it and the mitochondrial matrix.

Question 4

Where does glycolysis take place?

Answer 4

In the cytoplasm of cells.

Question 5

Is glycolysis an aerobic or anaerobic process and why?

Answer 5

It is an anaerobic process and doesn’t need oxygen to take place. Glycolysis is the 1st stage of both aerobic and anaerobic respiration.

Question 6

What is stage one of glycolysis?

Answer 6

Phosphorylation -

1) Glucose is phosphorylated by adding 2 phosphates from 2 molecules of ATP. This creates 1 molecule of hexose biphospate and 2 molecules of ATP.
2) The hexose biphosphate is split up into 2 molecules of triose phosphate (TP).

Question 7

What is the second stage of glycolysis?

Answer 7

Oxidation -

1) TP is oxidised forming 2 molecules of pyruvate.
2) NAD collects the hydrogen ions, forming 2 molecules of reduced NAD.
3) 4 ATP are produced, but 2 were used up in stage one, so there is a net gain of 2 ATP.

Question 8

What happens to the products of glycolysis?

Answer 8

> 2 molecules of reduced NAD go to the last stage (oxidative phosphorylation).
2 pyruvate molecules are actively transported into the matrix of the mitochondria for the link reaction.

Question 9

What happens in stage 2 - the link reaction?

Answer 9

1)Pyruvate is decarboxylated (1 C is removed from pyruvate in the form of CO2).
2)NAD is reduced - it collects hydrogen from pyruvate, changing pyruvate into acetate.
3)Acetate is combined with coenzyme A (CoA) to form acetyl coenzyme A (acetyl CoA)
>No ATP is produced in this reaction.

Question 10

Where does the link reaction take place?

Answer 10

In the mitochondrial matrix.

Question 11

How many times does the link reaction occur for each glucose molecule?

Answer 11

Twice for each glucose molecule makes 2 pyruvate molecules.

Question 12

Describe the steps of the Krebs cycle?

Answer 12

1) Acetyl CoA from the link reaction combines with oxalooacetate to form citrate (citric acid). This is catalysed by citrate synthase.
2) Coenzyme A goes back to the link reaction to be used again.
3) The 6C citrate molecule is converted to a 5C molecule.
4) Decarboxylation occurs where CO2 is removed.
5) Dehydrogenatioon also occurs, where H is removed.
6) The H is used to produced reduced NAD from NAD.
7) The 5C molecule is then converted to a 4C molecule
8) Decarboxylation and dehydrogenation occur, producing one molecule of reduced FAD and two of reduced NAD.
9) ATP is produced by the direct transfer of a phosphate group from an intermediate compound to ADP.
10) Citrate has now been converted into oxaloacetate.

Question 13

What is it called when a phosphate group is directly transferred from one molecule to another?

Answer 13

Substrate-level phosphorylation.

Question 14

What products from the Krebs cycle go to the oxidative phosphorylation stage?

Answer 14

> 3 reduced NAD

>1 reduced FAD

Question 15

What happens to the other products of the Krebs cycle?

Answer 15

> 1 coenzyme A is reused in the next link reaction.
Oxaloacetate is regenerated for use in the next Krebs cycle.
2 CO2 is released as a waste product.
1 ATP is used for energy.

Question 16

Where does oxidative phosphorylation occur?

Answer 16

In the inner mitochondrial membrane.

Question 17

Describe the step by step process of oxidative phosphorylation?

Answer 17

1) H atoms are released from reduced NAD (NADH) and FAD as they’re oxidised to NAD and FAD. The H atoms split into protons (H+) and electrons (e-).
2) The e- move along the electron transport chain (made up of 3 electron carriers).
3) This energy is used by the electron carriers to pump protons from the mitochondrial matrix into the intermembrane space.
4) The conc. of protons is now higher in the intermembrane space than in the mitochondrial matrix - forms an electrochemical gradient.
5) H+ move down the electrochemical gradient back into the mitochondrial matrix, via ATP synthase. This drives the synthesis of ATP from ADP and an inorganic phosphate.
6) In the mitochondrial matrix, at the end of the transport chain, the protons, electrons and O2 (from the blood) combine to form water. Oxygen is said to be the final electron acceptor.

Question 18

What is an electrochemical gradient?

Answer 18

A conc. gradient of ions.

Question 19

How many ATP molecules can be made from one glucose molecule and which stages do they come from?

Answer 19

> Glycolysis -
Produce 2 ATP
Produce 2 NADH -> 2 x 2.5 = 5 ATP

> Link reaction (x2) -
2 NADH -> 2 x 2.5 = 5

Krebs cycle (x2) - 
2 ATP
6 NADH -> 6 x 2.5 = 15
2 reduced FAD -> 2 x 1.5 = 3

32 ATP in total.

Question 20

What are the 2 types of anaerobic respiration?

Answer 20

> Lactate fermentation

>Alcoholic fermentation

Question 21

What is similar about the 2 processes of anaerobic respiration?

Answer 21

> Both take place in the cytoplasm.

>Both start with glycolysis (which produces pyruvates).

Question 22

Describe the process of lactate fermentation?

Answer 22

1) NADH (from glycolysis) transfers hydrogen to pyruvate to form lactate and NAD.
2) NAD can then be reused in glycolysis.

Question 23

How can glycolysis continue even when there isn’t much oxygen around?

Answer 23

The production of lactate regenerates NAD. Glycolysis needs NAD in order to take place. Therefore, a small amount of ATP can still be produced to keep some biological processes going.

Question 24

How does the body tolerate lactate?

Answer 24

> Our cells can tolerate a high level of lactate for short periods of time, e.g. short periods of hard exercise. However, too much lactate is toxic and is removed from the cells into the bloodstream. The liver takes up lactate from the bloodstream and converts it back into glucose in a process called gluconeogenesis.

Question 25

Describe anaerobic respiration in yeast cells/plant cells?

Answer 25

Alcoholic fermentation occurs in yeast cells-
1)CO2 is removed from pyruvate to form ethanal.
2)Reduced NAD (from glycolysis) transfers H to ethanal to form ethanol and NAD.
3)NAD can then be reused in glycolysis.
The production of ethanol also regenerates NAD so glycolysis can continue when there is little oxygen around.

Question 26

Compare the yield of energy between anaerobic or aerobic respiration and why?

Answer 26

> The ATP yield from anaerobic respiration is always lower than aerobic respiration.
Anaerobic respiration only includes one energy-releasing stage (glycolysis) which only produces 2 ATP per glucose molecule.
The other energy releasing reactions of the Krebs cycle and oxidative phosphorylation need oxygen, so they can’t occur during anaerobic respiration.

Question 27

What is a respiratory substrate and give 3 other examples other than glucose?

Answer 27

A respiratory substrate is any biological molecule that can be broken down in respiration to release energy.
>Cells also respire other carbohydrates, lipids and proteins.