21: Respiration

Question 1

State the definition of respiration.

Answer 1

Respiration is a gradual, controlled enzymatic oxidation of food that releases energy in the forms of heat and ATP.

Question 2

State the overall word equation for respiration.

Answer 2

Glucose + oxygen – (enzymes) –> carbon dioxide + water

Question 3

State 3 similarities between burning and respiration.

Answer 3

1. Both processes are oxidative.
2. Both process produce carbon dioxide and water while releasing energy.
3. Oxygen is needed in both burning and aerobic respiration (not anaerobic respiration).

Question 4

List 4 differences between burning and respiration.

Answer 4

1. Site of occurrence: Burning occurs outside cells while respiration occurs inside living cells.
2. Enzyme involvement: Burning does not involve enzymes while each reaction in respiration is catalysed by a specific enzyme.
3. Release of energy: Burning has an uncontrolled release of energy in a single reaction while respiration has a controlled release of energy in a stepwise manner in many reactions.
4. Formation of ATP: Burning releases energy as light and heat while respiration releases energy in the forms of ATP and heat.

Question 5

State 4 features of the process of respiration.

Answer 5

1. Respiration releases energy from food through the controlled oxidative breakdown of food.
2. Respiration involves many steps, each of which is catalysed by a specific enzyme.
3. Respiration takes place in all living cells.
4. Respiration uses glucose as the most common substrate.

Question 6

Explain the meaning of oxidative breakdown.

Answer 6

Oxidative breakdown refers to the breaking down of a compound by oxidation.

Question 7

Name the process in which ATP is formed by combining a phosphate with ADP.

Answer 7

Phosphorylation

Question 8

Name the process in which ATP is broken down into a phosphate and ADP.

Answer 8

Hydrolysis

Question 9

Explain how ATP can supply energy to cells.

Answer 9

ATP can be readily broke down into ADP and a phosphate with the release of a small amount of energy. The energy is sufficient to drive individual reactions in cells.

Question 10

Name 5 common cellular activities which require energy from ATP.

Answer 10

1. Synthesis of biomolecules (eg. protein synthesis)
2. Muscular contraction
3. Cell division
4. Transmission of nerve impulses
5. Active transport (eg. food absorption, mineral absorption)

Question 11

State 3 main types of activities for which cells require energy from ATP and provide examples.

Answer 11

1. Movement: muscle contraction, movement of cilia in ciliated epithelium and movement of chromosomes during cell division.
2. Synthesis: synthesis of proteins and DNA.
3. Transport: pumping molecules or ions across cell membranes by active transport during mineral absorption by plant roots, and absorption of digested food across the wall of the alimentary canal in animals.

Question 12

State two features of ATP as an energy carrier.

Answer 12

1. ATP acts as an energy carrier in the cell which it is made, and it cannot be transferred from cell to cell.
2. The energy released from the oxidative breakdown of one glucose molecule can be used to form many ATP molecules in the cell. In this way, the large amount of energy stored in a glucose molecule is packaged into a smaller amount in each ATP molecule.

Question 13

State two aspects in which photosynthesis and respiration facilitates within an ecosystem.

Answer 13

Cycling of molecules, and flow of energy.

Question 14

Explain how photosynthesis and respiration contribute to the cycling of molecules in the ecosystem.

Answer 14

The products of photosynthesis are glucose and oxygen, which are used as the raw materials for respiration. Similarly, the products of respiration are carbon dioxide and water, which are used as the raw materials for photosynthesis. This forms the basis for the recycling of matter in the ecosystem.

Question 15

Explain how photosynthesis and respiration contribute to the flow of energy in the ecosystem.

Answer 15

During photosynthesis, light energy from the surroundings is changed to chemical energy and stored in organic food. The energy is transferred to consumers through feeding along food chains.
Through respiration, organisms break down organic food and release the energy as ATP and heat.
In photosynthesis, ATP transfers light energy captured by chlorophyll to make organic compounds. In respiration, ATP transfer the energy released by the oxidative breakdown of organic compounds to drive cellular metabolism.

Question 16

State one function of the outer membrane of the mitochondrion.

Answer 16

It controls the movement of substances into and out of the mitochondrion.

Question 17

State the properties and functions of the inner membrane of the mitochondrion.

Answer 17

The inner membrane is highly folded to form cristae (crista). The cristae are packed with enzymes involved in the reactions of respiration, and they greatly increase the surface area for packing more enzymes.

Question 18

State the properties and functions of the mitochondrial matrix.

Answer 18

The mitochondrial matrix is the space enclosed by the inner membrane of the mitochondrion. It contains enzymes involved in the reactions of respiration. It also provides a fluid medium for reactions to take place.

Question 19

Name 6 types of cells which are abundant in mitochondria.

Answer 19

Liver cell, muscle cell, synaptic knob, epithelial cells of an intestinal villus, sperms, rod cells.

Question 20

Name the type of respiration that requires oxygen.

Answer 20

Aerobic respiration

Question 21

State the definition of aerobic respiration.

Answer 21

Aerobic respiration is the complete oxidative breakdown of food to release energy with the presence of oxygen.

Question 22

State the 3 main stages of aerobic respiration.

Answer 22

1. Glycolysis
2. Krebs cycle
3. Oxidative phosphorylation

Question 23

State the location in which glycolysis occurs.

Answer 23

Cytoplasm

Question 24

Name all reactants and products of glycolysis.

Answer 24

Reactants: glucose, 2 NAD, 2 ATP, 4 ADP + 4P
Products: 2 pyruvate, 2 NADH, 4 ATP

Question 25

Describe the process of the 2 steps of glycolysis.

Answer 25

1. Glucose is **activated by phosphorylation** and broken down into two triose phosphate molecules, **using 2 ATP molecules**. 2. The two triose phosphate molecules are **oxidised** by NAD to form **2 pyruvate molecules, 2 NADH, and 4 ATP molecules**.

Question 26

State the number of pyruvate molecules formed from one glucose molecule undergoing glycolysis.

Answer 26

2

Question 27

State the number of ATP and NADH molecules formed from one glucose molecule undergoing glycolysis.

Answer 27

A **net amount** of 2 ATP is formed (4 are formed, and 2 are used), while 2 NADH are formed.

Question 28

State the location in which the bridging between glycolysis and Krebs cycle occurs.

Answer 28

Mitochondrial matrix

Question 29

State the location in which Krebs cycle occurs.

Answer 29

Mitochondrial matrix

Question 30

Describe the process of bridging between glycolysis and Krebs cycle.

Answer 30

The pyruvate formed in glycolysis **enters the mitochondrion** where reactions of the Krebs cycle occur. It is converted to a **2-C compound**, releasing **1 carbon dioxide molecule**. After releasing 1 NADH, and combining with a molecule of coenzyme A, **acetyl-CoA** is formed, which carries the acetyl group into the Krebs cycle.

Question 31

Name all products which one pyruvate molecule has been converted into in the bridging between glycolysis and Krebs cycle.

Answer 31

1 Acetyl-CoA molecule, 1 carbon dioxide

Question 32

Name all reactants and products of the bridging reaction between glycolysis and Krebs cycle.

Answer 32

Reactants: pyruvate, NAD, Coenzyme A Products: carbon dioxide, NADH, acetyl-CoA

Question 33

State the number of carbon dioxide and NADH molecules formed from one glucose molecule undergoing bridging between glycolysis and Krebs cycle.

Answer 33

Each pyruvate molecule produces 1 carbon dioxide and 1 NADH. Each glucose molecule produces 2 pyruvate molecules in glycolysis. So, 2 carbon dioxide molecules, and 2 NADH are produced.

Question 34

State the 2 main stages of the Krebs cycle.

Answer 34

1. Combination of acetyl-CoA with 4-C compound 2. Regeneration of 4-C compound

Question 35

Describe the process when acetyl-CoA is combined with the 4-C compound in the Krebs cycle.

Answer 35

Acetyl-CoA combines with a 4-C compound which is **already present in the mitochondrial matrix**. The 2-C acetylene group is donated to the 4-C compound to **form a 6-C compound**. **Coenzyme A is released** and regenerated continually, so it can carry other acetylene groups formed from pyruvate in glycolysis into the Krebs cycle.

Question 36

Describe the process when the 4-C compound is regenerated in the Krebs cycle.

Answer 36

The 6-C compound is oxidised step by step to **regenerate** the original 4-C compound. Each of the reactions in the process is catalysed by a different enzyme. The 6-C compound **loses 2 carbon atoms** which are released as carbon dioxide. It is **oxidised** by NAD and FAD, to produce **3 NADH and 1 FADH**. The energy released from the conversion is used to make **1 ATP molecule**.

Question 37

State the number of ATP, CO₂, FADH, and NADH molecules formed from one acetyl-CoA molecule in the Krebs cycle.

Answer 37

1 ATP, 2 CO₂, 1 FADH, 3 NADH

Question 38

State the number of ATP, CO₂, FADH, and NADH molecules formed from one glucose molecule in the Krebs cycle.

Answer 38

2 ATP, 4 CO₂, 2 FADH, 6 NADH

Question 39

State the number of ATP, CO₂, FADH, and NADH molecules formed from one glucose molecule in the bridging reactions and the Krebs cycle.

Answer 39

2 ATP, 6 CO₂, 2 FADH, 8 NADH

Question 40

State the net number of ATP, CO₂, FADH, and NADH molecules formed from one glucose molecule from glycolysis to the end of the Krebs cycle.

Answer 40

4 ATP, 4 CO₂, 2 FADH, 8 NADH

Question 41

State the location in which oxidative phosphorylation occurs.

Answer 41

Inner mitochondrial membrane

Question 42

Describe the process of the oxidation of NADH in oxidative phosphorylation.

Answer 42

1. NADH is **oxidised to NAD**. The hydrogen atoms split into hydrogen ions and electrons. The regenerated NAD can accept hydrogen in glycolysis and Krebs cycle again. 2. The electrons take part in a series of **redox reactions** along an **electron transport chain**, which consists of electron carriers embedded in the **inner membrane of the mitochondria**. The energy released in the reactions is used to make ATP. 3. The hydrogen ions and the electrons are eventually transferred to **oxygen**, to form **water**.

Question 43

Explain the effect on the Krebs cycle if no oxygen is present as the final hydrogen (electron) acceptor.

Answer 43

If no oxygen is available to accept the hydrogen from NADH and FADH produced in aerobic respiration, NAD and FAD **cannot be regenerated**. As a result, Krebs cycle **cannot proceed** because there are no NAD and FAD to accept hydrogen from the splitting of molecules.

Question 44

Explain the effect on glycolysis if no oxygen is present as the final hydrogen (electron) acceptor.

Answer 44

If no oxygen is available to accept the hydrogen from NADH produced in aerobic respiration, NAD **cannot be regenerated**. As a result, glycolysis **cannot proceed** because there is no NAD to accept hydrogen from the splitting of molecules.

Question 45

State the number of ATP molecules formed from one NADH molecule in oxidative phosphorylation.

Answer 45

3

Question 46

State the number of ATP molecules formed from one FADH molecule in oxidative phosphorylation.

Answer 46

2

Question 47

State the number of ATP molecules formed from the NADH and FADH from the breakdown of one glucose molecule in aerobic respiration.

Answer 47

34

Question 48

State the total number of ATP molecules formed from the breakdown of glucose in aerobic respiration.

Answer 48

38

Question 49

State the balanced overall chemical equation of aerobic respiration.

Answer 49

C₆H₁₂O₆ + 6O₂ -> 6CO₂ + 6H₂O

Question 50

State the source of the oxygen atoms in water in the overall equation of aerobic respiration.

Answer 50

Oxygen gas (NOT glucose)

Question 51

State the difference in site of occurrence of aerobic respiration and photosynthesis.

Answer 51

Aerobic respiration occurs in the cytoplasm and mitochondria of **all living cells** while photosynthesis occurs in **chloroplast-containing cells** only.

Question 52

Contrast the type of metabolism of aerobic respiration and photosynthesis.

Answer 52

Aerobic respiration belongs to **catabolism** where organic food is broken down by **oxidation** to release energy. Photosynthesis belongs to **anabolism** where organic food is built ip by **reduction** to store energy.

Question 53

State the energy transformation of aerobic respiration and photosynthesis.

Answer 53

In aerobic respiration, chemical energy in organic food is converted to ATP and heat. In photosynthesis, light energy is converted to chemical energy in organic food.

Question 54

Compare and describe the activation process and products formed from aerobic respiration and photosynthesis.

Answer 54

Both reactions require an **activation step**. In aerobic respiration, glucose is activated by **phosphorylation** using ATP, which is then broken down in a controlled manner in **glycolysis** for forming ATP and NADH. In photosynthesis, **chlorophyll** is activated by **light absorption** and electrons are excited to a high energy level.

Question 55

Compare and describe the cyclic processes of aerobic respiration and photosynthesis.

Answer 55

In **Krebs cycle** in aerobic respiration, carbon dioxide is removed from pyruvate, forming NADH, FADH, ATP, and regenerating the 4-C compound. In **Calvin cycle** in photosynthesis, carbon dioxide is fixed into the cycle by a 5-C compound. NADPH and ATP are used to from triose phosphate which subsequently forms glucose. The 5-C compound is regenerated using energy from ATP.

Question 56

Compare and describe the electron transport of aerobic respiration and photosynthesis.

Answer 56

Both processes involve electron transport, in which energy released is used to **form ATP**. In aerobic respiration, electrons in NADH and FADH are **finally accepted by oxygen** and ATP is formed by **oxidative phosphorylation**. In photosynthesis, electrons from chlorophyll are **finally accepted by NADP** to form NADPH, and ATP is formed from **photophosphorylation**.

Question 57

Name the type of respiration that does not require oxygen.

Answer 57

Anaerobic respiration

Question 58

State the location in which anaerobic respiration occurs.

Answer 58

In the cytoplasm only.

Question 59

Explain the meaning of alcoholic fermentation.

Answer 59

Alcoholic fermentation is the process in which **yeast respires anaerobically** in **insufficient supply of oxygen** to produce ethanol and carbon dioxide.

Question 60

Describe the process of alcoholic fermentation.

Answer 60

During alcoholic fermentation, the pyruvate formed from glycolysis is **reduced to ethanol**. Carbon dioxide is released and NAD is regenerated to pick up hydrogen in glycolysis again.

Question 61

State the overall word equation of alcoholic fermentation.

Answer 61

glucose -> energy (2 ATP) + ethanol + carbon dioxide

Question 62

State the number of ATP molecules produced when one molecule of glucose undergoes alcoholic fermentation.

Answer 62

2

Question 63

Explain the difference in the number of ATP molecules formed from aerobic respiration and alcoholic fermentation.

Answer 63

Aerobic respiration produces 38 molecules of ATP while alcoholic fermentation only produces 2. In alcoholic fermentation, glucose is **only partially broken down** into ethanol and carbon dioxide. A large amount of chemical energy is still trapped inside the ethanol formed. Therefore, **much less energy** is released from alcoholic fermentation compared to aerobic respiration.

Question 64

Explain the meaning of lactic acid fermentation.

Answer 64

Lactic acid fermentation is a process in which **skeletal muscle cells** or bacteria carry out **anaerobic respiration** to produce **lactic acid** with the release of a small amount of energy.

Question 65

Describe the process of lactic acid fermentation.

Answer 65

During lactic acid fermentation, the pyruvate formed from glycolysis is **reduced to lactic acid**. NAD is regenerated to pick up hydrogen in glycolysis again, and the lactic acid is released to the blood.

Question 66

State the overall word equation of lactic acid fermentation.

Answer 66

glucose -> energy (2 ATP) + lactic acid

Question 67

State the significance of lactic acid fermentation in skeletal muscles.

Answer 67

Compared with aerobic respiration, lactic acid fermentation comprises relatively **simple reactions**. During **strenuous exercise**, skeletal muscles need a lot of energy from breaking down glucose. Though the blood supply to the muscles increases, there is still an **insufficient supply of oxygen** for complete oxidation of glucose in the muscles. In addition to aerobic respiration, muscles also carry out lactic acid fermentation. This **provides additional energy in a very short time**, so muscles can contract **more powerfully and at a higher rate**.

Question 68

Describe two ways in which lactic acid is removed after exercise.

Answer 68

We keep **breathing fast and deeply** for a period of time in order to take in **extra oxygen**. With more oxygen, **more NAD is regenerated** in the electron transport chain. Then the lactic acid can be **oxidised by NAD to pyruvate**, which can be converted to acetyl-CoA for entering the Krebs cycle. The remaining lactic acid is **converted to glycogen** for storage in the liver and muscles.

Question 69

Explain the meaning of oxygen debt.

Answer 69

Oxygen debt is the **additional amount of oxygen** required to remove all the lactic acid, after skeletal muscle cells have undergone lactic acid fermentation.

Question 70

Explain why slow jogging is more effective than sitting to remove lactic acid from muscles when recovering from vigorous exercise.

Answer 70

Jogging increases the rate of breathing and heart rate. A faster rate of breathing increases the amount of **oxygen** breathed into the lungs. A faster heart rate increases the rate of **blood flow** to deliver more oxygen to the muscles to oxidise the lactic acid.

Question 71

State three applications of alcoholic fermentation in yeast.

Answer 71

1. Beer and wine brewing 2. Bread-making 3. Production of biofuel

Question 72

State two applications of lactic acid fermentation.

Answer 72

1. Making yoghurt and cheese 2. Pickling vegetables

Question 73

State the reason why different end products can be produced from pyruvate molecules in different organisms in anaerobic respiration.

Answer 73

Different organisms have **different enzymes** which control different metabolic pathways.