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AQA Biology3.5.2 Respiration

Name: ______________________

Lesson Exam Question Marks

Homework Checked

Date

Lesson 1 – Mitochondrial Structure /30

Lesson 2 – Stage 1: Glycolysis /35

Lesson 3 – Stage 2: Link Reaction /13

Lesson 4 – Stage 3: Krebs cycle /29

Lesson 5 – Stage 4: Oxidative Phosphorylation/ETC /36

Lesson 6 – RQ and Respiratory Substrates /10

End of Topic Test

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Specification Section

3.5.2 Respiration Respiration produces ATP.

Glycolysis is the first stage of anaerobic and aerobic respiration. It occurs in the cytoplasm and is an anaerobic process.

Glycolysis involves the following stages:

phosphorylation of glucose to glucose phosphate, using ATP production of triose phosphate oxidation of triose phosphate to pyruvate with a net gain of ATP and reduced NAD.

If respiration is only anaerobic, pyruvate can be converted to ethanol or lactate using reduced NAD. The oxidised NAD produced in this way can be used in further glycolysis.

If respiration is aerobic, pyruvate from glycolysis enters the mitochondrial matrix by active transport.

Aerobic respiration in such detail as to show that:

pyruvate is oxidised to acetate, producing reduced NAD in the process acetate combines with coenzyme A in the link reaction to produce acetylcoenzyme A acetylcoenzyme A reacts with a four-carbon molecule, releasing coenzyme A and producing a six-

carbon molecule that enters the Krebs cycle in a series of oxidation-reduction reactions, the Krebs cycle generates reduced coenzymes and ATP

by substrate-level phosphorylation, and carbon dioxide is lost synthesis of ATP by oxidative phosphorylation is associated with the transfer of electrons down the

electron transfer chain and passage of protons across inner mitochondrial membranes and is catalysed by ATP synthase embedded in these membranes (chemiosomotic theory)

other respiratory substrates include the breakdown products of lipids and amino acids, which enter the Krebs cycle.

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Key word list for 3.5.2

Aerobic Connective with the presence of free oxygen. Aerobic respiration requires free oxygen to release energy from glucose

Anaerobic Connected with the absence of oxygen. Anaerobic respiration releases energy from glucose or other foods without the presence of oxygen

ATP (adenosine triphosphate)

Nucleotide found in all living organisms, which is produced during respiration and is important in the transfer of energy

Diffusion The movement of molecules or ions form a region where there are in high concentration to one where their concentration is lower

Electron Negatively charged sub-atomic particle that orbits the positively charged nucleus of all atoms

Electron carrier molecule

A chain of carrier molecules along which electrons pass, released energy in the form of ATP as they do so

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Electron Transport Chain

Use of electrons from the Krebs Cycle to synthesise ATP via a series of oxidation-reduction reactions

Facilitated diffusion

Diffusion involving the presence of protein carrier molecules to allow the passive movement of substances across plasma membranes

Glycolysis First part of cellular respiration in which glucose is broken down anaerobically in the cytoplasm to two molecules of pyruvate

Hydrolysis The breaking down of large molecules into smaller ones by the addition of water molecules

Krebs cycle Series of aerobic biochemical reactions in the matrix of the mitochondria of most eukaryotic cells by which energy is obtained through the oxidation of acetylcoenzyme A produced from the breakdown of glucose

Link reaction The process linking glycolysis with the Krebs cycle in which hydrogen and carbon dioxide are removed from pyruvate to form acetylcoenzyme A in the matrix of the mitochondria

Metabolism All the chemical processes that take place in living organismsNAD

(nicotinamide adenine

dinucleotide)

A molecule that carriers electrons and hydrogen ions during aerobic respiration

Oxidation Chemical reaction involving the loss of electronsOxidation-reduction

A chemical reaction I which electrons are transferred from one substance to another substance. Losing electrons is oxidised, gaining electrons is reduced

Oxidative phosphorylation

The formation of ATP in the electron transport system of aerobic respiration

Substrate A substance that is acted on or used by another substance or processSubstrate-level phosphorylation

The formation of ATP by the direct transfer of a phosphate group from a reactive intermediate to ADP

Lesson 1 – Mitochondria StructureBy the end of this lesson you should be able to:

Describe respiration as a metabolic pathway Describe and explain the structure of the mitochondrion and its adaptations for respiration

Notes:Respiration Recap:All living cells respire. During respiration a chemical reaction occurs in which sugars are oxidised to release energy. Carbon dioxide and water are released during these reactions. Glucose enters cells by diffusion and facilitated diffusion. When there is a shortage of oxygen, anaerobic respiration in muscles produces lactate.

Carbohydrates and fats store chemical energy, these organic molecules are broken down. The energy that is released from breaking the bonds is used to synthesise ATP. ATP is known as the universal energy currency and drives biological processes and chemical reactions that occur within cells. The sum of chemical reactions that occur in the body is known as metabolism. Metabolic reactions can either be anabolic or catabolic.

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● Anabolic – building larger molecules from smaller molecules – requires energy as its making bonds

● Catabolic – breaking larger molecules into smaller molecules – releases energy as its breaking bonds

Respiration is known as a metabolic pathway as it is a many stepped process with each step controlled and catalysed by a specific enzyme.

Mitochondria Structure and Function

Found in all eukaryotic cell types. Found in higher numbers in cells that have

higher energy demands. 1µm diameter 10µm long. Mitochondrial DNA

Some cells e.g muscle cells, sperm cells, epithelial cells in small intestine, and nerve cells, will have large amounts of mitochondria to provide the large amounts of ATP they require for: building complex molecules, protein synthesis, movement (active transport, swimming or muscle contraction), cell division, endo/exocytosis (e.g cells that secrete substances) and transmitting nerve impulses.

Stages of RespirationThe process of respiration can be split into 4 stages:

1. Glycolysis = In the cytoplasm of the cell.

2. Link reaction = In the Matrix of the mitochondria.

3. Krebs Cycle = Also in the matrix.

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4. Electron Transport Chain = Proteins found in the membrane of the cristae in the mitochondria.

Recall Questions: 1. What is aerobic respiration?2. What is a metabolic pathway?3. Describe the membrane of the mitochondria4. What is the name of the fluid inside the mitochondria?5. What is contained in the matrix?6. How is the inner membrane adapted for respiration?7. The membrane also contains proteins for the ETC. What is an ETC?8. Oxidative phosphorylation in mitochondria is similar to

photophosphorylation in chloroplasts. These processes are involved in the formation of what compound?

9. What is the name of the enzyme that is involved in synthesising this compound?10. Chemiosmosis (covered in photosynthesis) depends on the creation of proton concentration

gradients. What sub-atomic particle provides the energy to maintain this gradient?11. What cells contain the most mitochondria? Give an example and explain.12. The figure above is a transverse section of a sperm cell. The mitochondria of sperm cells form a

spiral around the central flagellum. Identify the structures labelled U, W, and Z13. Where do most of the stages of respiration take place in the cell?14. What are the stages of respiration?15. The matrix is the fluid filled space inside the mitochondria. Which 2 reactions take place here?

Exam Questions: Q1. (b) The table shows features of a mitochondrion and a chloroplast. Complete the table with ticks where a feature is present.

(3)Feature Mitochondrion Chloroplast

Double outer membrane

Starch grains

Diffusion of oxygen into the organelle

(c) Give the function of a mitochondrion.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________(1)

Q2. During respiration where, exactly, in a cell does each of the following occur?

(i) Glycolysis

______________________________________________________________(1)

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(ii) Electron transfer chain

______________________________________________________________(1)

Q3. The diagram shows a mitochondrion.

(a) Name the parts labelled X and Y.

(i) X ______________________________

(ii) Y ______________________________(2)

Scientists isolated mitochondria from liver cells. They broke the cells open in an ice-cold, isotonic solution. They then used a centrifuge to separate the cell organelles. The diagram shows some of the steps in the process of centrifugation.

(b) Suggest which pellet, A, B or C contained the mitochondria. (1)

(c) Explain why the solution used was

(i) ice-cold

______________________________________________________________

______________________________________________________________(1)

(ii) isotonic.

______________________________________________________________

______________________________________________________________

______________________________________________________________

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______________________________________________________________(2)

(d) People with mitochondrial disease have mitochondria that do not function properly.

Some people with mitochondrial disease can only exercise for a short time. Explain why a person with mitochondrial disease can only exercise for a short time.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________(2)

Q4. (b) The diagram is of a mitochondrion at a magnification of × 30 000.

Calculate the actual length of this mitochondrion in micrometres (µm). Show your working.

Answer = ____________________ µm (2)

(c) Some scientists support the theory that mitochondria are organelles that evolved from prokaryotic cells.

(i) Give one piece of evidence that supports the theory that mitochondria evolved from prokaryotic cells.

______________________________________________________________

______________________________________________________________

______________________________________________________________ (1)

(ii) What is the advantage to cells of having mitochondria?

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________(2)

Q5. Cells constantly hydrolyse ATP to provide energy.

(a) Describe how ATP is resynthesised in cells.

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___________________________________________________________________

___________________________________________________________________ (2)

(b) Give two ways in which the hydrolysis of ATP is used in cells.

1. _________________________________________________________________

___________________________________________________________________

2. _________________________________________________________________

___________________________________________________________________(2)

(c) This is a photograph (micrograph) of a mitochondrion taken using a scanning electron microscope.

What is the evidence that a scanning electron microscope was used to take this photograph?

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________(1)

(d) Name the part of the mitochondrion labelled X in the photograph.

___________________________________________________________________(1)

(e) The actual length of the mitochondrion between points A and B in the photograph is 4 μm.

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What is the magnification of the mitochondrion in the photograph?

Show your working.

Magnification ____________________ (2)

Q6. The diagram shows the structure of a mitochondrion.

(a) In which part of the mitochondrion does the Krebs cycle take place?

___________________________________________________________________(1)

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

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________(2)Homework:

Watch the following videos to learn how mitochondrial DNA can be used to map human evolution

Mother of Humanity -Mitochondrial Eve (2:15) https://www.youtube.com/watch?v=rx_oUd-05ys

TED Talk: A family tree for humanity (8:27) https://bit.ly/30YamqU

Recall Question Answers:

What is aerobic respiration?

splitting of glucose to release CO2 as a waste product and combining H2 with atmospheric O2 with the release of a large amount of energy

What is a metabolic pathway? many stepped process with each step controlled and catalysed by a specific intracellular enzyme

Describe the membrane of the mitochondria Double membrane, inner membrane folded to form cristae.

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What is the name of the fluid inside the mitochondria? MatrixWhat is found in the fluid inside the mitochondria?

Ribosomes, Mitochondrial DNA, Enzymes for the link reaction and Krebs cycle

How is the inner membrane adapted for respiration?

Highly folded to increase surface area for ATP production. Lots of membrane bound electron carrier proteins and ATP synthase enzymes for generating ATP.

The membrane contains proteins for the ETC. What is an ETC?

A series of membrane bound proteins that can transfer electrons between them

Oxidative phosphorylation in mitochondria is similar to photophosphorylation in chloroplasts. These processes are involved in the formation of what compound? ATPWhat is the name of the enzyme that is involved in synthesising this compound? ATP synthaseChemiosmosis (covered in photosynthesis) depends on the creation of proton concentration gradients. What sub-atomic particle provides the energy to maintain this gradient? H+ ions

What cells contain the most mitochondria? Give an example and explain.

Cells which require large amounts of ATP e.g muscle cells (for movement), sperm cells (for movement), root cells (for active transport), epithelial cells of small intestine (for active transport)

The figure above is a transverse section of a sperm cell. The mitochondria of sperm cells form a spiral around the central flagellum. Identify the structures labelled U, W, and Z

U = matrixW = CristaeZ= Outer membrane/intermembrane space

Where do most of the stages of respiration take place in the cell? The mitochondria

What are the stages of respiration? Glycolysis, link reaction, Krebs cycle, electron transport chain

The matrix is the fluid filled space inside the mitochondria. Which 2 reactions take place here? The link reaction and the Krebs cycle

Lesson 2 – Stage 1: Glycolysis By the end of this lesson you should be able to:

Describe the process of glycolysis Describe the products of anaerobic respiration

Video: BioRach – Glycolysis - https://bit.ly/3g3QWVH

Notes:Glycolysis (Glyco - glucose and Lysis – splitting) is the first stage of aerobic respiration AND anaerobic respiration as it does not require oxygen. It occurs outside of the mitochondria in the cytoplasm of all living cells. There are two stages: phosphorylation (1-2) and oxidation (4). You will notice this is the reverse of the Calvin cycle in photosynthesis!

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Products of glycolysis (for 1 molecule of glucose): 2 reduced NAD – goes to the ETC 2 Pyruvate – Actively transported into the mitochondria for the link reaction 2 ATP – Used for energy

Anaerobic RespirationDuring anaerobic respiration the products of glycolysis are converted into ethanol or lactate using reduced NAD. Alcoholic fermentation occurs in plants and yeast

Anaerobic respiration regenerates NAD so that glycolysis can continue even when there isn’t enough oxygen – this allows a small amount of ATP to be produced to allow some biological processes to continue. After a period of anaerobic respiration lactate is oxidised back into pyruvate. The oxygen needed to do this is known as the oxygen debt and it is the reason you breathe heavier after a period of intense exercise. Pyruvate can be oxidised back into CO2 and H2O via the Krebs Cycle. Some lactate is converted to glycogen and stored in muscle or liver cells.Recall Questions:

1. What is the first stage of respiration?2. Where does the first stage take place in the cell? 3. What happens during phosphorylation in glycolysis? 4. What happens during oxidation in glycolysis?5. How many ATP molecules are produced during glycolysis?6. What is the only stage of respiration common to aerobic and anaerobic respiration?7. What are the productsof glycolysis?8. Why is the production of reduced NAD important?9. Where do the products of glycolysis go?

Glucose is phosphorylated by adding 2 phosphates from 2 molecules of ATP. This makes it a more reactive molecule.

It splits to produce 2 x 3C molecules of TP

The triose phosphate is oxidised (loses hydrogen and phosphate) to form 2 molecules of pyruvate. NAD collects the hydrogen ions forming 2 reduced NAD4 ATP are produced, but 2 were used at the start, so there’s a net gain of 2ATP

Lactate fermentation occurs in animal cells and bacteria

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10. Why is the ATP from glycolysis only 2?11. What happens to lactate after a period of anaerobic respiration? 12. What is oxygen debt?

Exam Questions: Q1. (a) The main stages in anaerobic respiration in yeast are shown in the diagram.

(i) Name process X.

______________________________________________________________(1)

(ii) Give one piece of evidence from the diagram which suggests that the conversion of pyruvate to ethanol involves reduction.

______________________________________________________________

______________________________________________________________(1)

(iii) Explain why converting pyruvate to ethanol is important in allowing the continued production of ATP in anaerobic respiration.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________(2)

(b) Give two ways in which anaerobic respiration of glucose in yeast is

(i) similar to anaerobic respiration of glucose in a muscle cell;

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1. ____________________________________________________________

______________________________________________________________

2. ____________________________________________________________

______________________________________________________________(2)

(ii) different from anaerobic respiration of glucose in a muscle cell.

1. ____________________________________________________________

______________________________________________________________

2. ____________________________________________________________

______________________________________________________________(2)

Q2. The diagram summarises the process of anaerobic respiration in yeast cells.

(a) (i) In anaerobic respiration, what is the net yield of ATP molecules per molecule of glucose?

________________________________________________

__________________________________________ (1)

(ii) Give two advantages of ATP as an energy-storage molecule within a cell.

1.________________________________________________

________________________________________________

2.________________________________________________

________________________________________________(2)

(b) Describe how NAD is regenerated in anaerobic respiration in yeast cells.

___________________________________________________________________

___________________________________________________________________(1)

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Q3. (a) Mitochondria in muscle cells have more cristae than mitochondria in skin cells. Explain the advantage of mitochondria in muscle cells having more cristae.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(b) Substance X enters the mitochondrion from the cytoplasm. Each molecule of substance X has three carbon atoms.

(i) Name substance X.

______________________________________________________________(1)

Q4.(a) Name the two substances produced by anaerobic respiration in humans.

1. _________________________________________________________________

2. _________________________________________________________________(2)

(b) When an athlete runs in a 100 metre race, 90% of the energy needed is provided by anaerobic respiration.

(i) Explain why most of the energy is provided by anaerobic respiration rather than aerobic respiration.

______________________________________________________________

______________________________________________________________

______________________________________________________________ (2)

(ii) The athlete continues to breathe deeply for several minutes after the race ends. Explain why this is necessary.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________(2)

Q5.(a) Pyruvate is formed in the breakdown of glucose during respiration. When there is

sufficient oxygen, this pyruvate is fully broken down. Name two substances formed from the pyruvate.

1. _________________________________________________________________

2. _________________________________________________________________ (1)

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(b) (i) If there is a shortage of oxygen in muscle cells during exercise, some pyruvate is converted into lactate. Explain why muscles become fatigued when insufficient oxygen is available.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________(2)

(ii) Some of the lactate is oxidised to pyruvate by muscles when they are well-supplied with oxygen. Suggest an advantage of the lactate being oxidised in the muscles.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________(2)

Q6. (a) During respiration where, exactly, in a cell does each of the following occur?

(i) Glycolysis

______________________________________________________________(1)

(ii) Electron transfer chain

______________________________________________________________(1)

(b) Without oxygen, less ATP is produced by respiration. Explain why.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

Q7. When one mole of glucose is burned, 2800 kJ of energy are released. However, when one mole of glucose is respired aerobically, only 40% of the energy released is incorporated into ATP. Each mole of glucose respired aerobically produces 38 moles of ATP.

(a) (i) Calculate how much energy is incorporated into each mole of ATP. Show your working.

Answer ____________________ kJ(2)

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(ii) When glucose is respired what happens to the energy which is not incorporated into ATP?

______________________________________________________________(1)

(b) (i) When one mole of glucose is respired anaerobically, only 2 moles of ATP are produced. Explain why less energy is released in anaerobic respiration.

______________________________________________________________

______________________________________________________________(1)

(ii) At the end of a sprint race, a runner continues to breathe rapidly for some time. Explain the advantage of this.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________(2)

Homework:

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Recall Question Answers - Glycolysis: What is the first stage of respiration? Glycolysis Where does the first stage take place in the cell? Cell cytoplasm

What happens during phosphorylation in glycolysis? Glucose is phosphorylated by adding 2 phosphate groups from 2 ATP molecules.

What happens during oxidation in glycolysis?Triose phosphate is oxidised forming 2 pyruvate molecules. 2 NAD molecules are reduced to 2 NADH.

How many ATP molecules are produced during glycolysis? 4 ATP are produced but the net gain is 2ATPWhat is the only stage of respiration common to aerobic and anaerobic respiration? Glycolysis What are the productsof glycolysis? 2 molecules of pyruvate, 2 reduced NAD and 2 ATPWhy is the production of reduced NAD important? It is needed for the ETC to produce ATPWhere do the products of glycolysis go? 2 reduced NAD – goes to the ETC

2 Pyruvate – Actively transported into the mitochondria for the link reaction

Why is the ATP from glycolysis only 2?

2 ATP are used to phosphorylate the glucose to make it more reactive, four ATP molecules are produced but the net (overall total) is 2.

What happens to lactate after a period of anaerobic respiration?

Lactate is oxidised back into pyruvate. It is directly oxidised into CO2 and H2O via Krebs Cycle. Some lactate is converted to glycogen and stored in muscle or liver cells.

What is oxygen debt?The oxygen needed to oxidise lactic acid in the period of recovery after exercise

Recall Question Answers – Link Reactoin: What is the second stage of respiration? The link reactionWhat are the products of the link reaction? CO2, Acetyl CoA, and reduced NAD

What happens in the link reaction? Pyruvate is oxidised and carboxylated to form acetate which combined with Coenzyme A to form Acetyl coenzyme A.

What are the products of the link reaction? Acetyl CoA + reduced NAD + CO2How many times do the Link reaction occur for every glucose molecule? twice

For each glucose molecule where do the products go?

2 acetyl coenzyme A (goes to Krebs cycle)2 CO2 released as waste2 Reduced NAD – goes to ETC

What is the role of coenzyme A in the link reaction? Transports Acetate to the Krebs cycle

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Lesson 3 – Stage 2: Link Reaction

By the end of this lesson you should be able to: Describe the process of the link reaction

Notes: The link reaction is the second stage of respiration, it LINKS glycolysis to the Krebs cycle. The products of the link reaction enter the Krebs cycle.

Products from the glycolysis are:

● 2x net ATP

● 2x reduced NAD (NADH)

● 2x Pyruvate

If oxygen is present pyruvate is transported into the mitochondrial matrix via active transport (so this requires energy.

Oxidative carboxylation:Removal of a CO2 and H+ from pyruvate producing acetate. The H+ ion is accepted by NAD forming reduced NAD.

The acetate combines with coenzyme A to form acetylcoenzyme A – this then enters the Krebs cycle.,

1 pyruvate molecule produces:o 1x CO2 = released as wasteo 1x reduced NAD = goes to the ETCo 1x acetyl CoA = Goes into the Krebs cycle

For each glucose molecule used in glycolysis, two pyruvate molecules are made, but the link reaction uses only one pyruvate molecule, so the link reaction and the Krebs cycle happen twice for every glucose molecule which goes through glycolysis.

Recall Questions:

1. What is the second stage of respiration?2. What are the products of the link reaction? 3. What happens in the link reaction? 4. What are the products of the link reaction? 5. How many times do the Link reaction occur for every glucose molecule?6. For each glucose molecule where do the products go?7. What is the role of coenzyme A in the link reaction?

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Exam Questions: Q1. (a) Describe how acetylcoenzyme A is formed in the link reaction.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________(2)

(c) In muscles, pyruvate is converted to lactate during anaerobic respiration.

(i) Explain why converting pyruvate to lactate allows the continued production of ATP during anaerobic respiration.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________(2)

(ii) In muscles, some of the lactate is converted back to pyruvate when they are well supplied with oxygen. Suggest one advantage of this.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________(1)

Q2. The biochemical pathway of aerobic respiration involves a number of different steps.

Name one step in which carbon dioxide is produced.

___________________________________________________________________(1)

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Q3. The diagram represents two of the stages of aerobic respiration that take place in a mitochondrion.

(a) Name substance X.

___________________________________________________________________(1)

(b) Which stage of aerobic respiration takes place inside a mitochondrion and is not represented on the diagram?

___________________________________________________________________(1)

Q5.(a) Mitochondria in muscle cells have more cristae than mitochondria in skin cells. Explain

the advantage of mitochondria in muscle cells having more cristae.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________(2)

(b) Substance X enters the mitochondrion from the cytoplasm. Each molecule of substance X has three carbon atoms.

(i) Name substance X.

______________________________________________________________(1)

(ii) In the link reaction substance X is converted to a substance with molecules effectively containing only two carbon atoms. Describe what happens in this process.

______________________________________________________________

______________________________________________________________

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______________________________________________________________ (2)

Homework:

IntroductionThis activity gives you the chance to analyse a data set that shows the relationship between storage temperature and respiration rate in a range of fruits and vegetables. The data have implications for how commercial crops are stored and transported, and for the potential use of hormone treatments to manipulate ripening. You will be employing skills you have developed during the course, such as recognising patterns, explaining causal relationships, and interpreting evidence.

Learning outcomeAfter completing this worksheet you should be able to:

describe, calculate, and explain patterns, relationships, and evidence in data for respiration rate and temperature.

BackgroundFruits and vegetables can continue to respire once they have been harvested and stored. Cellular respiration can enable ripening to continue when the product is stored. The rate of respiration varies between species. The table below shows the respiration rates of various types of fruit and vegetable at different storage temperatures.

Type of fruit or vegetable

Respiration rate (mg CO2 kg1 h1)

At 0 °C At 5 °C At 10 °C At 15 °C At 20 °C

Apple 3 6 9 15 20

Asparagus 60 105 215 235 270

Blackberry 19 36 62 75 115

Cauliflower 17 21 34 44 69

Onion 3 5 7 7 8

Orange 4 6 8 18 28

Parsnip 12 13 22 37 n/a

Potato n/a 12 16 17 22

Turnip 8 10 16 23 25

Questions1 Describe how respiration rate changes as temperature increases in:

a asparagus

(3 marks)

b onion.

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(4 marks)

2 Which fruit or vegetable shows:a the greatest percentage increase in respiration rate between 0 °C and 20 °C?

Show your working.

(2 marks)

b the smallest percentage increase in respiration rate between 0 °C and 20 °C? Show your working.

(2 marks)

3 Calculate the respiration rate in mg CO2 g1 s1 of:a blackberry at 20 °C.

(3 marks)

b parsnip at 15 C.

(3 marks)

Give your answers in standard form and to two significant figures.

4 What can you conclude from the data about:a the optimal storage conditions for harvested fruits and vegetables?

(2 marks)

b which fruit(s) or vegetable(s) would be the easiest to store and maintain in an edible condition at room temperature in a cupboard? Explain your answer.

(3 marks)

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Lesson 4 – Sage 3: Krebs Cycle

By the end of this lesson you should be able to: • Describe the Krebs cycle• Explain the importance of coenzymes in respiration

Video: BioRach - Link reaction and Krebs cycle: https://bit.ly/30ZFZR6

Notes:1. Acetate is removed from the CoenzymeA and combines with a 4C molecule of oxaloacetic acid to form a 6C sugar called citrate. Coenzyme A goes back to the link reaction.

2. Citrate is decarboxylated and dehydrogenated – 2 H+ ions are used to reduce NAD

3. Now a 5C compound it is decarboxylated and dehydrogenated again to produce another CO2 and another reduced NAD.

4. Now a 4C molecule, a phosphate is removed and used to generate a molecule of ATP. This is known as substrate-level phosphorylation

5. The 4C compound is dehydrogenated again and 2 H+ ions reduce FAD.

6. Finally one more dehydrogenation produces oxaloacetate.

For each molecule of glucose the Krebs cycle turns twice , producing: 4 carbon dioxides – waste product 6 x reduced NAD – to the ETC 2 x reduced FAD – to the ETC 2 x ATP

Most of the ATP in respiration is made in the ETC!

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Importance of coenzymes in cellular respiration:Coenzyme A NAD FAD

Stages Link reaction Glycolysis x2 Link reaction x 2Krebs x6

Krebs x 1

What it transports Acetyl group 1 H+ 2 H+

Role in ETC - Oxidised at the start of ETC Oxidised further along the ETC

Amount of ATP synthesised per molecule

3 ATP 2 ATP

Recall Questions:1. Where does the Krebs cycle takes place?2. How is citrate formed?3. How many molecules of reduced NAD are produced in the Krebs cycle per molecule of glucose?4. Name the coenzymes used within the Krebs cycle5. What are the products of one Krebs cycle? 6. What is released from NADH and FADH2 when they are oxidised?7. How many turns of the Krebs cycle for one molecule of glucose?8. Which coenzyme can synthesise more ATP?

Exam Questions: Q1. (b) In the Krebs cycle, acetylcoenzyme A combines with four-carbon oxaloacetate to form six-carbon citrate. This reaction is catalysed by the enzyme citrate synthase.

(i) Oxaloacetate is the first substrate to bind with the enzyme citrate synthase. This induces a change in the enzyme, which enables the acetylcoenzyme A to bind.

Explain how oxaloacetate enables the acetylcoenzyme A to then bind to the enzyme.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (2)

(ii) Another substance in the Krebs cycle is called succinyl coenzyme A. This substance has a very similar shape to acetylcoenzyme A.

Suggest how production of succinyl coenzyme A could control the rate of the reaction catalysed by citrate synthase.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (2)

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Q2. (a) The table contains statements about three stages of respiration.

Complete the table with a tick if the statement in the first column is true for each stage of respiration in an animal.

Glycolysis Link reaction Krebs cycle

Occurs inmitochondria

Carbon dioxideproduced

NAD is reduced

(3)

Q3. The boxes in the diagram represent substances in glycolysis, the link reaction and the Krebs cycle.

(a) Complete the diagram to show the number of carbon atoms present in one molecule of each compound.

(2)

(b) Other substances are produced in the Krebs cycle in addition to the carbon compounds shown in the diagram. Name three of these other products.

1. _________________________________________________________________

2. _________________________________________________________________

3. _________________________________________________________________(3)

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Q4. (a) The flow chart shows the main stages in aerobic respiration.

(i) Complete the flow chart by writing, in the appropriate boxes, the number of carbon atoms in substance P and the name of substance Q.

(2)

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Q5. The diagram gives an outline of the process of aerobic respiration.

(a) Name substances X, Y and Z.

X ________________________________________________________________

Y ________________________________________________________________

Z ________________________________________________________________(3)

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(b) Give the location of each of the following in a liver cell.

(i) Glycolysis ____________________________________________________

(ii) The Krebs cycle _______________________________________________(2)

(c) (i) Write the letter A on the diagram to show one step where ATP is used.

(ii) Write the letter B on the diagram at two steps where ATP is produced.(3)

(d) Apart from respiration, give three uses of ATP in a liver cell.

1. _________________________________________________________________

2. _________________________________________________________________

3. _________________________________________________________________(3)

Q6. The table contains some statements relating to biochemical processes in a plant cell. Complete the table with a tick if the statement is true or a cross if it is not true for each biochemical process (4)

Statement Glycolysis Krebs cycle

Light-dependent reaction of

photosynthesis

NAD is reduced

NADP is reduced

ATP is produced

ATP is required

Homework:

Recall Question Answers Lesson 4:

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Where does the Krebs cycle takes place?Matrix inside mitochondria

How is citrate formed? Acetate from acetyl coenzyme A combines with oxaloacetate

How many molecules of reduced NAD are produced in the Krebs cycle per molecule of glucose? 6Name the coenzymes used within the Krebs cycle

CoEnzyme A, NAD, FADWhat are the products of one Krebs cycle? ATP, 2 CO2, 3 reduced NAD and reduced FADWhat is released from NADH and FADH2 when they are oxidised? Hydrogen atomsHow many turns of the Krebs cycle for one molecule of glucose?

2Which coenzyme can synthesise more ATP? NAD

Recall Question Answers Lesson 5:

What is chemiosmosis?

The movement of hydrogen ions across a selectively permeable membrane down their electrochemical gradient to generate ATP

What is oxidative phosphorylation ?The process where the energy carried by electrons from NADH and FADH2 is used to make ATP

Where do the electrons come from at the start of the electron transport chain?

Oxidation of reduced NAD and reduced FADWhat is the energy released from electrons as they move down their electron transport chain used for?

Used by electron carriers to pump H+ ions into the intermembrane space

How is ATP made in electron transport chain?

H+ ions move down the electrochemical gradient back into the mitochondrial matrix via the ATP synthase enzyme. This movement drives the synthesis of ATP

What is the final electron acceptor in respiration ? OxygenHow much ATP is produced from the ETC? 28How much ATP is produced in total? 32What happens to energy that is not used to make ATP? Generates heatHow efficient is respiration (%)? 32%

Give a reason why respiration is not more efficient

Some ATP is used up moving hydrogen from reduced NAD made during glycolysis into the mitochondria.

Some ATP is used up moving pyruvate into the mitochondria by active transport.

Some energy is lost as heat. This heat helps to maintain a suitable body temperature for enzyme-controlled reactions

Lesson 5 – Stage 4: Oxidative Phosphorylation

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By the end of this lesson you should be able to: Describe and explain how ATP is produced in the mitochondria

Videos: BioRach: Oxidative phosphorylation - https://bit.ly/3aqfjfk summary video - https://bit.ly/2CvtR0F

Notes: Oxidative phosphorylation is the process where the energy carried by electrons from reduced coenzymes is used to make ATP., it relies on chemiosmotic theory. The theory of chemiosmosis states that the energy in a chemical gradient established by electron movement is used to generate ATP. This movement of protons (H+) down the concentration gradient releases energy that is used to create ATP from ADP + P i in cellular respiration as well as photosynthesis.

Chemiosmosis depends on the creation of proton concentration gradient. This energy comes from high-energy (excited) electrons. Electrons are raised to this higher energy level in 2 ways.

● Photosynthesis – Electrons found within pigment molecules in chloroplasts (e.g. Chlorophyll) are excited by absorbing light from the Sun

● Respiration – High energy electrons are released when chemical bonds in glucose are broken down within

mitochondria.

In respiration OP takes place within the folded inner membrane of the mitochondria called cristae. Excited electrons are taken to an electron transport chain (ETC) in the mitochondrial membrane by the reduced coenzymes NAD and FAD. When they are oxidised, they release protons and electrons. The electrons pass along the ETC through a series of redox reactions, releasing energy. The energy is used to move protons into the intermembrane space. They diffuse back, down the concentration gradient, through ATP synthase which combines ADP and Pi to produce ATP. Three protons are required to synthesis one ATP molecule.

At the end of the ETC the electrons, protons and oxygen (from the blood) combine to form water. This means that oxygen is the final electron acceptor in the ETC.

Evidence to support chemiosmotic theory: The proton gradient across the inner membrane can be measured as it corresponds to a pH

gradient. Isolated ATP synthase enzymes can produce ATP using a proton gradient even if no electron

transport is occurring. Chemicals that block the ETC inhibit the formation of a proton gradient and prevent ATP synthesis.

Intermembrane space

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Calculating the Total ATP

ATP produced before the ETC: 4 molecules of ATP are produced in glycolysis (2 are used up so NET is only 2) 2 molecules of ATP are produced from two turns of the Krebs cycle.

Each reduced NAD can produce 2.5 ATP and each reduced FAD can produce 1.5 ATP.

ATP produced in the ETC: Glycolysis = 2 x reduced NAD = 5 ATP Link Reaction = 2 x reduced NAD = 5 ATP Krebs Cycle = 6 x reduced NAD = 15 ATP Krebs Cycle = 2 reduced FAD = 3 ATP

Respiration Total = 32 ATP

Efficiency:

The theoretical yield of 32 ATPs for each glucose molecule is rarely achieved. In fact, respiration is only about 32% efficient because:

Some ATP is used up moving hydrogen from reduced NAD made during glycolysis into the mitochondria.

Some ATP is used up moving pyruvate into the mitochondria by active transport. Some energy is used to generate heat. This helps to maintain a suitable body temperature for

enzyme-controlled reactions.

Recall Questions:1. What is oxidative phosphorylation?2. What is chemiosmosis?3. Where do the electrons come from at the start of the electron transport chain?4. What is the energy released from electrons in the electron transport chain used to do? 5. How is ATP made in electron transport chain?6. What is the final electron acceptor in respiration?7. How much ATP is produced from the ETC?8. How much ATP is produced in respiration in total?9. What happens to energy that is not used to make ATP?10. How efficient is respiration (%)?11. Give a reason why respiration is not more efficient

Exam Questions:

Q2. Describe the role of oxygen in aerobic respiration.

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Q7. (b) Describe how ATP is made in mitochondria.

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(c) Plants produce ATP in their chloroplasts during photosynthesis. They also produce ATP during respiration. Explain why it is important for plants to produce ATP during respiration in addition to during photosynthesis.

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Q3. The diagram shows some of the stages in two processes that produce ATP.

(a) In Process 1, what causes substance X to lose electrons (e–)?

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(b) Where precisely, within a cell, does electron transport take place in Process 2?

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Q8. Explain why oxygen is needed for the production of ATP on the cristae of the mitochondrion.

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Q6.(a) Describe the part played by the inner membrane of a mitochondrion in producing ATP.

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Q4.(a) The table contains some statements relating to biochemical processes in a plant cell.

Complete the table with a tick if the statement is true or a cross if it is not true for each biochemical process.

Statement Glycolysis Krebs cycle

Light-dependent reaction of

photosynthesis

NAD is reduced

NADP is reduced

ATP is produced

ATP is required

(4)

(b) An investigation was carried out into the production of ATP by mitochondria. ADP, phosphate, excess substrate and oxygen were added to a suspension of isolated mitochondria.

(i) Suggest the substrate used for this investigation.

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(ii) Explain why the concentration of oxygen and amount of ADP fell during the investigation.

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(iii) A further investigation was carried out into the effect of three inhibitors, A, B and C, on the electron transport chain in these mitochondria. In each of three experiments, a different inhibitor was added. The table shows the state of the electron carriers, W–Z, after the addition of inhibitor.

Inhibitor added

Electron carrier

W X Y Z

A oxidised reduced reduced oxidised

B oxidised oxidised reduced oxidised

C reduced reduced reduced oxidised

Give the order of the electron carriers in this electron transport chain. Explain your answer.

Order _______ _______ _______ _______

Explanation ____________________________________________________

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Q5. (a) The table contains statements about three biological processes.

Complete the table with a tick if the statement in the first column is true, for each process.

Photosynthesis Anaerobic respiration

Aerobic respiration

ATP produced

Occurs in organelles

Electron transport chain involved

(3)

(b) Write a simple equation to show how ATP is synthesised from ADP.

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(c) Give two ways in which the properties of ATP make it a suitable source of energy in biological processes.

1. _________________________________________________________________

2. _________________________________________________________________

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Summary Video Bozeman Science: http://www.bozemanscience.com/cellular-respiration

Homework:

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http://www.bozemanscience.com/cellular-respiration

Lesson 6 – Respiratory Quotient and Respiratory Substrates

By the end of this lesson you should be able to: Describe how to calculate the respiratory quotient Explain how other respiratory substrates can be used for respiration

Videos: BioRach-Respiratory substrates: https://bit.ly/2EaZXiQ

Notes: A respiratory substrate is any organic molecule broken down to release energy for the synthesis of ATP.

Lipids

● Triglycerides are hydrolysed into fatty acids, and

glycerol by lipase enzymes.

● Glycerol is converted to pyruvate before

undergoing oxidative decarboxylation, producing an acetyl group which binds with coenzyme A and forms Acetyl CoA.

● Fatty acids are converted to Acetyl CoA.

● Lipids store and release 2x as much energy as

carbohydrates.

Proteins

● Proteins have to be hydrolysed into amino acids

● Then deaminated (removal of amine group)

before they can enter the respiratory pathway via pyruvate.

● This requires ATP, so the net production of ATP from protein is reduced.

Gram for gram, in terms of net energy release biological macromolecules are arranged in this order.Lipids > Alcohols > Proteins > Carbohydrates

The respiratory quotient of a substrate is the ratio of CO2 to O2 produced/consumed to break down that molecule.

RQ¿ CO2 producedO2consumed

The balanced symbol equation for aerobic respiration is 6O2 + C6H12O6 6CO2 + 6H2O therefore:

Carbohydrates RQ¿ CO2 producedO2consumed = RQ¿ 6

6 = 1.0

RQ Proteins = 0.8-0.9

RQ Lipids = 0.7

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If the respiratory quotient is calculated to be greater than one, it indicates anaerobic respiration is occurring because more carbon dioxide is being produced than oxygen being consumed.

Practice Questions:

1. Suggest what the following RQ values indicate about the type of respiration occurring in an organism:a. 1.10b. 0.98c. 0.77

2. Calculate the RQ of the insect at rest and in flight

3. Which substrate is used being used when at rest an in flight?

4. Use the data in the table to suggest the likely diet of each genus of honeypot ant:

Exam Question:Q1.

In an investigation, the effects of caffeine on performance during exercise were measured. One group of athletes (A) was given a drink of decaffeinated coffee. Another group (B) was given a drink of decaffeinated coffee with caffeine added. One hour later the athletes started riding an exercise bike and continued until too exhausted to carry on. Three days later the same athletes repeated the experiment, with the drinks exchanged.

(a) (i) The researchers added caffeine to decaffeinated coffee. Explain why they did not just use normal coffee.

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(ii) The performance of the athletes might have been influenced by how they expected the caffeine to affect them. How could the researchers avoid this possibility?

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During the exercise the concentrations of glycerol and fatty acids in the blood plasma were measured. The results are shown in the table.

Drink Mean time to exhaustion

/minutes

Mean concentration ofblood glycerol/

mmol dm–3

Meanconcentration of

blood fatty acids/

mmol dm–3

With caffeine 90.2 0.20 0.53

Without caffeine 75.5 0.09 0.31

(b) (i) Describe the effect of caffeine on exercise performance.

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(ii) Suggest one explanation for the higher glycerol and fatty acid concentrations in the blood plasma of the athletes after they were given caffeine.

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(c) The researchers measured the volumes of carbon dioxide exhaled and oxygen inhaled during the exercise. From the results they calculated the respiratory quotient (RQ), using the formula

When a person is respiring carbohydrate only, RQ = 1.0

When a person is respiring fatty acids only, RQ = 0.7

(i) The basic equation for the respiration of glucose is

C6H12O6 + 6O2 → 6CO2 + 6H2O

Explain why the RQ for glucose is 1.0.

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(ii) The researchers found that, when the athletes were given the drink containing caffeine, their mean RQ was 0.85. When given the drink without caffeine their mean RQ was 0.92.

The researchers concluded that when the athletes had caffeine they used glycogen more slowly than when they did not have caffeine, and that the store of glycogen in their muscles was used up less quickly during the exercise.

Explain the evidence from the information above and from the table which supports these conclusions.

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Homework:

IntroductionThis worksheet asks you to look at alternative substrates for respiration. This will give you a more realistic idea of respiration, as it rarely just involves the metabolism of glucose or carbohydrates. You will need a good knowledge of aerobic respiration. You will also need your knowledge of common biological molecules.

Learning outcomesAfter completing this worksheet you should be able to:

describe and apply the difference in relative energy values of carbohydrates, lipids, and proteins as respiratory substrates

apply knowledge and understanding of practical investigations into the effect of factors such as temperature, substrate concentration, and different respiratory substrates on the rate of respiration

state that glucose is not the only substrate available for respiration explain the different ATP outputs from the different substrates explain what the respiratory quotient is.

BackgroundRespiratory substratesThe normal substrate for respiration is glucose. Although there is some glucose in the blood, most is stored as glycogen in the liver and muscles. When these reserves run low, many animal cells are able to use fats without the need to convert them to sugars. The fats are first broken down into fatty acids and glycerol. Cells can also use protein

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as a respiratory substrate. This is only when carbohydrate and fat stores have been used up. Proteins must first be broken down into amino acids and then the amine group removed via a process called deamination. This produces molecules called keto acids.

Glycerol, fatty acids, and keto acids do not enter the respiratory pathway at the same place that glucose would. In fact there are several places where each can enter the pathway. The diagram below shows how some of these molecules can be utilised during aerobic respiration.

Figure 1Just like glucose, glycerol must undergo phosphorylation for its conversion to triose phosphate. This process requires the hydrolysis of one ATP molecule but also generates three ATP molecules.

Fatty acids are converted to acetyl coenzyme A in a process called β-oxidation. Each acetyl coenzyme A molecule produced only requires two carbon atoms from the fatty acid chain, so each molecule of acid can produce many molecules of acetyl coenzyme A. These then enter the Krebs cycle as usual.

The respiratory quotient (RQ) is one way of finding which substrate is being used for respiration. RQ is the ratio of the amount of carbon dioxide produced to the amount of oxygen used up. During the respiration of glucose, six molecules of carbon dioxide are produced for every six molecules of oxygen used, so the ratio is one to one or 1.0. The table below shows the RQ values of common substrates.

Substrate RQGlucose 1.0

Protein 0.9

Fats 0.7

C6H12O6 + 6O2 → 6CO2 + 6H2O so:

6CO26O2

=1 .0

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Questions1 State the net gain of ATP molecules during glycolysis from where glycerol enters the chemical

pathway, and describe it.

(3 marks)

2 About 200 molecules of ATP are produced during the respiration of a molecule of fat. Explain how so many ATP molecules are produced.

(3 marks)

3 Using your knowledge of anaerobic and aerobic respiration together with the information provided, determine whether any of glycerol, fatty acids, or keto acids can be used in anaerobic respiration. Using your knowledge of where glycerol, fatty acids, and keto acids join the respiratory pathway and which parts of aerobic respiration stop when there is no oxygen available, determine whether these molecules can be used for anaerobic respiration.

(2 marks)

4 Palmitin (C51H98O6) is a fat. It requires 145 molecules of oxygen for every two molecules that are respired. Explain, using a balanced chemical equation, why the RQ for this fat would be lower than the RQ for glucose.

(2 marks)

5 Glucose is more readily used than fats or proteins as a respiratory substrate. Suggest why.

(2 marks)

6 The respiration of fats requires more oxygen than the respiration of glucose. Suggest why.

(3 marks)

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