CfE Higher Biology - Duncanrig Secondary School · Unit 1: Cell Biology ... During cellular respiration energy is ... CfE Higher Biology Pupil Course Notes Page of 25

CfE Higher Biology Pupil Course Notes

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Higher Biology

Unit 2: Metabolism and Survival

Topic 2: Respiration


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Sub Topic: Respiration

I can state that:

All living cells carry out respiration.

ATP is the energy currency of the cell and can be regenerated from ADP and

inorganic phosphate.

ATP has the role of providing the energy requirements for cellular processes.

The first stage of respiration is glycolysis.

Glycolysis involves the breakdown of glucose to pyruvate in the cytoplasm.

During the oxidation of pyruvate the enzyme dehydrogenase promotes the

removal of hydrogen and electrons from pyruvate and also the transfer of

hydrogen and electrons to its electron acceptor NAD.

The process of phosphorylation (the addition of a phosphate group to ADP to

form ATP) during glycolysis results in the production of 2 ATP molecules.

In the absence of oxygen, pyruvate undergoes fermentation to form lactate

(in animals and some bacteria) and ethanol and carbon dioxide (in plants and

fungi).

The citric acid cycle occurs in the matrix of the mitochondria.

During the citric acid cycle acetyl from acetyl co-enzyme A combines with

oxaloacetate to produce citrate.

Dehydrogenase enzymes catalyse the removal of hydrogen and electrons on 4

occasions from the various respiratory substrates during the cycle: NAD is the

hydrogen acceptor on three, FAD once.

Hydrogen and electrons are carried by NAD and FAD to the electron transport

chain.

The electron transport chain is a series of protein carrier molecules.

ATP synthase is used to catalyse the production of ATP form ADP and Pi.

The electron transport chain occurs on the inner membrane of the

mitochondria.

The final electron acceptor is oxygen which combines with hydrogen to form

water.

Most of the ATP generated by cellular respiration occurs as a result of the

electron transport chain.

The substrates for respiration are the carbohydrates; glucose, starch,

glycogen and other sugar molecules.

When carbohydrate is not available other substrates such as proteins or fats

can be used by the cell.


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Prior Learning:

National 5 Biology:

Unit 1: Cell Biology Sub-topic 8: Respiration

• the chemical energy stored in glucose must be released by all cells through a series of enzyme-controlled reactions called respiration;

• the energy released from the breakdown of glucose is used to generate ATP from ADP and phosphate;

• the chemical energy stored in ATP can be released by breaking it down to ADP and phosphate;

• ATP can be regenerated during respiration; • each glucose molecule is broken down via pyruvate to carbon dioxide and

water in the presence of oxygen, and yields 38 molecules of ATP; • the breakdown of each glucose molecule via the fermentation pathway yields

two molecules of ATP; • in the absence of oxygen in animal cells, glucose is broken down into lactate

via pyruvate; • in the absence of oxygen in plant and yeast cells, glucose is broken down into

alcohol/ethanol and carbon dioxide via pyruvate; • fermentation occurs in the cytoplasm; • aerobic respiration starts in the cytoplasm and is completed in the

mitochondria


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The Importance of Adenosine Triphosphate (ATP)

Cellular respiration is a series of metabolic pathways which releases the chemical

energy from food molecules and makes it available to the cell in the form of ATP. It

occurs in all living organisms in each of the three domains of life.

The Structure of Adenosine Triphosphate (ATP)

The structure of ATP must first be considered to understand how Adenosine

Triphosphate (ATP) provides the energy for the chemical reactions in cells.

Structure of an ATP and ADP molecules:

A molecule of adenosine triphosphate is made up of an adenosine joined to three

inorganic phosphates (Pi).

ATP is a high energy containing molecule. Energy is released when the high energy

bond which holds the third phosphate group to the rest of the molecule is broken

down by enzyme action.

This results in the formation of Adenosine diphosphate (ADP) which has

adenosine and two inorganic phosphate groups with a free inorganic phosphate

group as shown below.

ATP is the energy currency in living cells. During cellular respiration energy is

released which is used to synthesise ATP from ADP and an inorganic phosphate

group. The formation of the ATP is enzyme controlled. The addition of a phosphate

group is known as phosphorylation. ATP is made continuously during the process

of cellular respiration.

and


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ATP and Energy Transfer

ATP molecules produced during the catabolic reactions of cellular respiration are

used by the cell immediately as a source of energy, to drive anabolic (energy

requiring) reactions such as; active transport, muscle contraction and protein

synthesis.

ADP + Pi ATP

Because of its energy transfer role, ATP is constantly being synthesised and broken

down again. An active cell will synthesise up to 2 million molecules of ATP per

second and each molecule of ATP produced will be used up within a second of its

formation.

Transfer of energy via ATP

Complete the diagram below to show the cycle of energy states of ATP and ADP + Pi.

Respiration

Energy transfer

Work done

glucose + oxygen

muscle

contracted

Energy released from bond breaking

Energy stored in bond when made

+ energy


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Answer the questions below.

Why is ATP so important in the cell (include the words anabolic and catabolic

reactions in your answer)?

____________________________________________________________________

____________________________________________________________________

____________________________________________________________________

Why does the body never have a store of ATP at any given time?

____________________________________________________________________

____________________________________________________________________

Watch your teacher demonstrate the effect of ATP on muscle contraction.

Aim: To demonstrate the effect of ATP on muscle tissue.

Answer the following questions:

Q1. What was the effect of the solution on each muscle strand?

Muscle 1 _____________________________________________________________

Muscle 2 _____________________________________________________________

Muscle 3 _____________________________________________________________

Results Muscle 1 in glucose

solution

Muscle 2 in

distilled water

Muscle 3 in

ATP solution

Initial length

(mm)

Final length (mm)

Change in

Length (mm)

Percentage

change in length (mm)


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Q2. Which liquid provides energy for contraction?

____________________________________________________________________

Q3. Which two experiments acted as controls and why were they included?

____________________________________________________________________

____________________________________________________________________

Q4. Why was percentage change in length rather that the difference in length used

to compare the results?

____________________________________________________________________

____________________________________________________________________

Q5. Why was a 5min interval allowed between measuring the initial and the final

measurements?

____________________________________________________________________

______________________________________________________________

Q6. Write a conclusion for this experiment.

____________________________________________________________________

____________________________________________________________________

____________________________________________________________________

Q7. A pupil repeated this experiment, keeping everything the same but using boiled

ATP solution instead of fresh ATP solution. Their results were very similar. What

does this indicate about the chemical nature of ATP?

____________________________________________________________________

____________________________________________________________________

____________________________________________________________________


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Metabolic pathways of Cellular Respiration

The main respiratory substrates are glucose, starch and glycogen, although other

respiratory substrates can be used when required.

The overall equation for cellular respiration of glucose is:-

glucose + oxygen carbon dioxide + water + ENERGY

C6H12O6 + 6O2 6CO2 + 6H2O + 38ATP

The process of cellular respiration occurs in all three domains of life. The process

consists of many chemical reactions each of which is controlled by a specific

enzyme. It involves hydrogen being removed from various respiratory substrates

by dehydrogenase enzymes and being used to yield ATP.

Cellular respiration experiment

Aim: To investigate the activity of dehydrogenase enzyme in yeast.

During respiration, glucose is gradually broken down and hydrogen is released at

various stages of the respiratory pathway. Each of these stages is controlled by a

group of enzymes called dehydrogenase. Yeast cells contain the enzyme

dehydrogenase, which removes hydrogen from the small quantities of stored food as

the yeast carries out cellular respiration.

Resazurin dye is a chemical which reacts with hydrogen and changes colour when

hydrogen is added to it:

Colour change Result

Stays blue Lacks hydrogen

Blue to pink Some hydrogen

Blue to colourless Much hydrogen

Collect: 3 boiling tubes, live yeast suspension, boiled yeast suspension, glucose

solution, water and resazurin dye.


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Method:

1. Place 10ml of live yeast suspension in tubes A and B and 10ml of boiled yeast

in tube C.

2. Add 10ml of glucose to both tubes A and C.

3. To tube B add 10ml of water.

4. Now add 1ml of resazurin dye to each tube.

5. Shake vigorously for 20 secs.

6. Then place in a water bath set at 35OC

for 5 mins.

Results:

Sample Resazurin Colour change

Reason

A

Live yeast suspension + glucose

B

Live yeast suspension + water

C

Boiled yeast suspension + glucose

Conclusion:

____________________________________________________________________

____________________________________________________________________

__________________________________________________________________


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Metabolic Pathways of Cellular Respiration

Cellular respiration consists of many enzyme controlled steps to ensure that energy

is released continuously.

Cellular respiration can be spilt into three stages:

1. Glycolysis occurs in the cytoplasm

2. The Citric Acid Cycle occurs in the matrix of the mitchondrion

3. The Electron Transport Chain occurs in the cristae of the mitochondrion

Stage 1: Glycolysis

Glycolysis occurs in the cytoplasm of the cell and does not require oxygen. It

involves a cyclic series of enzyme controlled reactions. Glycolysis means ‘sugar

splitting’ and this describes the splitting of the glucose molecule eventually forming

pyruvate. The splitting of one glucose molecule requires 2ATP molecules (the

energy investment phase) to start the process. Glucose is broken down to

intermediate compounds by the process of phosphorylation (addition of a

phosphate donated by ATP ADP + Pi +energy). As the series of reactions

proceed 4 ATP molecules are generated (the energy pay off phase). Thus

glycolysis gives a net gain of 2 ATP.

During glycolysis, dehydrogenase enzymes release the hydrogen and high energy electrons from the respiratory substrate. The coenzyme molecule NAD (nicotinamide adenine dinucleotide) forms NADH to transport these to stage 3 of the process.

The process of glycolysis does not require oxygen. However, NADH only leads to

the production of further molecules of ATP at a later stage in the respiratory process

if oxygen is present. In the absence of oxygen, fermentation occurs.

Glycolysis

Occurs in the

cytoplasm of

the cell


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Structure of the mitochondrion

When oxygen is present, aerobic respiration occurs in the cell’s mitochondria.

These organelles are present in the cytoplasm and have a specialised structure. The

mitochondrion is bound by a double unit membrane. The inner membrane has many

folds called cristae, which give it a very large surface area. The cristae is the location

of the electron transport chain which is the main site of ATP production. The fluid

filled central cavity is called the matrix and it is rich with enzymes, which are

involved in the citric acid cycle.

Name the parts indicated in the diagram of a mitochondrion.

A ________________

B ________________

C ________________

D ________________

Stage 2: The Citric Acid Cycle

The citric acid cycle can only proceed if oxygen is present and it occurs in the

central cavity called the matrix of the mitochondrion. This stage involves a series

of enzyme controlled cyclic reactions.

Pyruvate diffuses into the matrix of the mitochondrion where it is broken down into

carbon dioxide and an acetyl group. The acetyl group combines with coenzyme A

to form acetyl coenzyme A. It is accompanied by the release of hydrogen and high

energy electrons which again bind temporarily to NAD to form NADH.

The acetyl coenzyme A releases the acetyl group which combines with a molecule of

oxaloacetate to form citrate. Enzymes control a series of reactions which break

down citrate to intermediate compounds eventually resulting in the regeneration

of oxaloacetate. During these reactions CO2 is released, 2ATP is generated and


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dehydrogenase enzymes remove hydrogen ions and electrons which are passed to

coenzymes NAD and FAD, forming NADH and FADH2 respectively.

NAD and FAD transport their hydrogen ions and high energy electrons to the

electron transport chain. This is the third and final stage of cellular respiration.

ADP+Pi ATP

To the Electron

Transport Chain


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Cellular Respiration Diagram Summary

ADP+Pi ATP

To the Electron

Transport Chain


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Stage 3: The Electron Transport Chain

The hydrogen ions and high energy electrons are passed to the electron transport

chain on the inner mitochondrial membrane. A great deal of energy is stored in

NADH and FADH2 which is then converted to ATP in this final phase of respiration.

The electron transport chain consists of 3 protein carrier molecules which act as pumps embedded in the inner membrane of the mitochondrion. Within the electron transport chain the hydrogen ions and electrons separate with the high energy electrons releasing their energy as they flow along the chain of 3 electron acceptors. The energy released is used to pump the hydrogen ions across the inner membrane into the inter membrane space maintaining a higher concentration of hydrogen ions between the inner and outer mitochondrial membranes. This forms a concentration gradient between the two areas. When the electrons come to the end of the chain they combine with the oxygen, the final electron acceptor. At the same time, oxygen combines with a pair of hydrogen ions to form water. As the hydrogen ions return via another protein molecule called ATP synthase they generate ATP.

The Synthesis of ATP


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Hydrogen ions return to the matrix by flowing through a channel in another protein molecule, this time an enzyme called ATP synthase. This movement of hydrogen ions causes part of the enzyme to rotate, driving it to synthesise ATP from ADP and Pi. Most of the energy produced in cellular respiration is produced in this way.

The transfer of electrons along the chain of acceptors releases sufficient energy to

produce 34 ATP molecules. This is known as oxidative phosphorylation.

The complete oxidation of one glucose molecule yields 38 ATP molecules in total; 2

ATP from glycolysis, 2 from Kreb’s cycle and a further 34 ATP from the electron

transfer chain.

Although oxygen only plays its role in this last stage, it is essential for the hydrogen

ions to pass along the electron transport chain. Without oxygen being present the

oxidation process cannot proceed beyond glycolysis.

Answer the ‘Testing Your Knowledge’ questions from Torrance page 149.


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Measuring the Rate of Cellular Respiration

A respirometer is a device used to measure the rate of cellular respiration. Factors

such as oxygen uptake or carbon dioxide production can be used to measure the

rate of respiration. As rate involved time, this must be measured during the

following experiment.

Your teacher will set up the experiment below to measure the rate of respiration in

soaked pea seeds.

Q1. What is the function of the soda lime?

__________________________________________________________

__________________________________________________________


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Q2. Describe what happened in experiment A and in the control experiment B.

Experiment A

Experiment B

Q3. What is the function of the syringes?

Q4. Explain why the change occurred in experiment A.

Q5. Why was it necessary to set up a control experiment?

Q6. Calculate the respiration rate in both experiments (i.e. the volume of oxygen

used in 1 hour).

Experiment A …………………… Experiment B …………………..

Collect the ‘Respirometers Question Sheet’ and answer the questions in your jotter.


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Other Respiratory Substrates

A respiratory substrate is a molecule from which energy can be liberated to produce

ATP in living cells.

In animal cells for instance: glucose is essential for some cells, e.g. brain cells, red

blood cells, and lymphocytes, but some cells, e.g. liver cells also oxidise fats and

excess amino acids.

Carbohydrates

Starch is a complex carbohydrate which is stored in plant cells and glycogen is a

complex carbohydrate store in animal cells. These complex molecules are made up

of long chains of ______________ molecules. They act as respiratory substrate

molecules as each can be broken down into ___________ as required. Other sugar

molecules such as maltose, sucrose and fructose can also be degraded into glucose

molecules or intermediates in the glycolytic pathway and therefore used as

respiratory substrates.

Fats

To use fats within cells these are first digested into ______ ______ and _________.

The long carbon chains of these molecules have many _______ atoms, providing a

rich source of energy.

Glycerol is converted to a glycolytic intermediate. Fatty acids are oxidised in the matrix of the _____________. Enzymes attack the ends of the long fatty acid chain

until it has been converted to acetyl coenzyme A.


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Protein

To use proteins within cells they are first digested into individual _______ _______.

Excess __________ __________ cannot be stored in the body. They undergo

deamination forming urea and respiratory intermediates as shown in the diagram.

These are then converted, through a series of reactions, to substances found in the

______ _____ ______.

Alanine, for example, is converted to _____________________, while

________________ is converted to acetyl coenzyme A with ______________ being

converted to an _________________ in the citric acid cycle.

During starvation, the body proteins can be converted to amino acids which can then

be utilised as an alternative respiratory substrate.

Answer the ‘testing Your Knowledge’ questions from Torrance page 155.


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It is important to remember that carbohydrates are utilised in glycolysis. However,

fats and proteins can only be respired aerobically, and do not undergo glycolysis.

Both are converted into substances which enter citric acid cycle, and then the


Fermentation

This is the process of energy production, in the absence of oxygen, generating only 2 ATP molecules due to the incomplete breakdown of the sugar molecules. As the cells are deprived of oxygen the citric acid cycle and electron transport chain cannot occur. Therefore, only glycolysis can take place and each glucose molecule can only generate 2ATP molecules as it is converted to pyruvate. The respiratory pathway that pyruvate then takes depends on the organism involved.

The diagram below outlines the process of fermentation.

Under normal circumstances the blood can supply oxygen to mammalian muscle tissue so that it can respire aerobically. However, during vigorous exercise the supply of oxygen to the muscle cells cannot meet the demand. This results in the

muscle cells undergoing fermentation.


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Comparison of aerobic respiration and fermentation.

Complete the table below outlining the differences in both processes.

Substance Aerobic respiration

Fermentation

In yeast In humans

Oxygen required?

Quantity of ATP?

Waste products produced?

Which type of respiration is most efficient? Give a reason for your answer.

Type of respiration: ____________________________________________________

Reason: ____________________________________________________

____________________________________________________

____________________________________________________


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Summary of Aerobic Respiration and Fermentation

Answer the ‘testing Your Knowledge’ questions from Torrance page 155.


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Look at the diagram of cellular respiration below and answer the questions

below.

E

Q1. Name the compounds labelled A and B in the diagram above.

A ______________________________

B ______________________________

Q2. Name the processes labelled 1, 2 and 3

1 _____________________________

2 _____________________________

3 _____________________________

Q3. Name the coenzyme labelled C

C ______________________________

Q4. Name the product labelled E.

E ______________________________

Q5. Name the final electron acceptor D

_______________________________


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(2.2) Cellular Respiration

I can state that:

1 2 3

All living cells carry out respiration

ATP is the energy currency of the cell and can be regenerated from ADP and

inorganic phosphate.

ATP has the role of providing the energy requirements for cellular processes.

The first stage of respiration is glycolysis.

Glycolysis is the breakdown of glucose to pyruvate in the cytoplasm.

During the oxidation of pyruvate the enzyme dehydrogenase promotes the

removal of hydrogen ions and electrons from pyruvate and also the transfer

of hydrogen and electrons to its acceptor NAD.

The process of phosphorylation (the addition of a phosphate group to ADP)

during glycolysis results in the production of 2 ATP molecules.

In the absence of oxygen, pyruvate undergoes fermentation to lactate (in

animals) and ethanol and carbon dioxide (in plants in fungi).

The citric acid cycle occurs in the matrix of the mitochondria.

During the Citric Acid Cycle acetyl co-enzyme A reacts with oxaloacetate to

produce citrate.

Dehydrogenase enzymes catalyse the removal of hydrogen and electrons on

4 occasions from the various respiratory substrates during the cycle: NAD is

the hydrogen acceptor on three, FAD once.

Hydrogen ions and electrons are carried by NAD and FAD to the electron

transport chain.

Complete:

Column 1 before your Unit assessment

Column 2 before your Prelim

Column 3 before your May exam


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(2.2) Cellular Respiration (cont.)

I can state that: 1 2 3

The electron transport chain is a series of protein carrier molecules.

ATP synthase is used to catalyse the production of ATP form ADP and Pi.

The electron transport chain occurs on the inner membrane of the

mitochondria.

The final electron acceptor is oxygen which combines with hydrogen ions to

form water.

Most of the ATP generated by cellular respiration occurs as a result of the


The substrates for respiration are the carbohydrates; glucose, starch,

glycogen and other sugar molecules.

When carbohydrate is not available other substrates such as proteins or fats

can be used by the cell.

Complete:

Column 1 before your Unit assessment

Column 2 before your Prelim

Column 3 before your May exam

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CfE Higher Biology - Duncanrig Secondary School · Unit 1: Cell Biology ... During cellular respiration energy is ... CfE Higher Biology Pupil Course Notes Page of 25