3.5 Chapter 12- Respiration

Question 1

What does respiration produce?

Answer 1

ATP (Adenosine Triphosphate).

Question 2

Why is respiration important?

Answer 2

• Glucose- can’t be used as a source of energy.
• Cells use ATP as their immediate energy source.
• ATP- formation from break down of glucose- occurs during cellular respiration.

Question 3

What does ATP stand for?

Answer 3

Adenosine Triphosphate

Question 4

Describe the structure of ATP?

Answer 4

• A nucleotide
• Ribose (pentose sugar)
• Adenine (an organic nitrogenous base)
• 3 phosphate groups

Question 5

Draw ATPs structure and label it.

Answer 5

Answer on revision card.

Question 6

What is the role of ATP?

Answer 6

Carries energy around the cell to where it’s needed.

Question 7

Describe how ATP is synthesised.

Answer 7

• ATP is formed in a condensation reaction between ADP (Adenosine Diphosphate) and inorganic phosphate (Pi).
• Requires energy from an energy releasing reaction (e.g. respiration or photosynthesis)
• Catalysed by by ATP synthase.
• This process is known as phosphorylation as a phosphate molecule is added to the ADP.

Question 8

When is ATP synthesised?

Answer 8

• During photosynthesis- photophosphorylation
• During respiration- oxidative phosphorylation
• When phosphate groups are transferred from donor molecules to ADP- substrate-level phosphorylation

Question 9

What is the function of ATP?

Answer 9

• ATP stores energy made in respiration in the chemical store of the phosphate bonds (bonds between phosphate groups).
• ATP diffuses to parts of the cell that need energy.

Question 10

How is energy released from ATP?

Answer 10

• ATP hydrolase (ATPase) breaks the phosphate bonds in a hydrolysis reaction (requiring water).
• Hydrolysing bonds- releases energy, splits the ATP into a ADP (Adenosine Diphosphate) and inorganic phosphate (Pi).
• The chemical energy released can then be used by the cell.

Question 11

What type of reaction is the hydrolysis of ATP?

Answer 11

• A reversible reaction.
• ADP and Pi are recycled to form ATP again.

Question 12

What is the formula of ATP reactions?

Answer 12

ATP + H₂O ⇌ ADP + Pi

Question 13

What are the benefits of using ATP as an energy source?

Answer 13

• Energy released in smaller, more manageable amounts, as it stores less energy, meaning little energy lost as heat.
• Small, soluable molecule- easily transported around the cell.
• ATP can be rapidly reformed once used up.
• Can’t leave cells so cells always have an immediate supply of energy.
• Immediate energy release- easily broken down by single reaction hydrolysis vs glucose/ other stores release- long process, several steps.
• Can make other molecules more reactive by transferring one of it’s phosphate groups (phosphorylation).
• Unstable and low activation energy, easily breakable bonds.

Question 14

Why does ATP have to be constantly remade and what does this require?

Answer 14

• Immediate energy release due to unstable bonds and single reaction hydrolysis.
• Requires ATP to be constantly remade in the mitochondria.
• Explains the large number of mitochondria.

Question 15

What are the uses of ATP?

Answer 15

• Metabolic processes- provides energy for making macromolecules e.g. starch, DNA.
• Muscle contraction- used for movement- more ATP hydrolysis means more muscle contraction.
• Active transport- changes the shape of carrier proteins.
• Secretion- needed to form lysosomes.
• Phosphorylation- activation of molecules- inorganic phosphate (Pi) can be added to other compounds to make them more reactive- lowers the activation energy especially in enzyme catalysed reactions.

Question 16

Describe ATP coupling.

Answer 16

ATP hydrolysis can be coupled to energy requiring reactions in the cell. The energy released is used directly to make reactions happen rather than being lost as heat.

Question 17

What are the problems of using ATP as an energy source?

Answer 17

• Not a long term energy source- can’t be stored as immediate energy source due to unstable phosphate bonds, whereas carbohydrates and fats can be used as storage.
• Stores less energy than glucose/ other stores.

Question 18

Why is energy important?

Answer 18

• Life depends on continuous transfers of energy.
• Needed in plants and animals for biological processes
• e.g. active transport, DNA replication, cell division, protien synthesis, maintainance of body temperature, muscle contraction.

Question 19

What is respiration evidence for?

Answer 19

Indirect evidence for evolution as respiration is universal- common in all organisms.

Question 20

What type of reaction is respiration?

Answer 20

A metabolic pathway- series of small reactions controlled by enzymes.

Question 21

Desribe respiration.

Answer 21

• Respiration is the release of energy from glucose or other substrates in plants and animals to form ATP.
• Respiration is important because cells can’t receive energy straight from glucose- it needs to be converted to ATP to be used as an immediate energy source.

Question 22

What are the two types of respiration?

Answer 22

• Aerobic respiration- requires oxygen- produces carbon dioxide, water and large amounts of ATP. Occurs in the mitochondria.
• Anaerobic respiration- occurs in the absence of oxygen- produces lactate (in animals) and ethanol and carbon dioxide in plants and fungi but little ATP.

Question 23

Describe the different forms of substrate in respiration.

Answer 23

• Glucose- used as a respiratory substrate in aerobic and anaerobic respiration.
• Other respiratory substrates can be used to provide energy to produce ATP in aerobic respiration- fatty acids from lipids and amino acids can be converted into molecules able to enter the Krebs cycle.

Question 24

How can respiration be limited?

Answer 24

Respiration is limited when the substrate decreases/ runs out, and carbon dioxide increases acidity or, for example lactate and **ethanol become toxic. **

Question 25

Describe the use of coenzymes in aerobic and anaerobic respiration.

Answer 25

• Coenzymes- molecules that aid the function of an enzyme by transferring a chemical group from one molecule to another. Some enzymes require these molecules to function.
• Coenzymes used in respiration- NAD, coenzyme A and FAD.
• NAD and FAD- transfer hydrogen from one molecule to another- reduce or oxidise molecules. They are reduced by the enzyme dehydrogenase.
• Coenzyme A- transfers acetate between molecules.

Question 26

How is energy from cellular respiration produced?

Answer 26

• Substrate-level phosphorylation- glycolysis and the Krebs cycle- direct transfer of phosphate from a respiratory intermediate to ADP- produces some ATP.
• Oxidative phosphorylation- electron transfer chain- indirect linking of energy from phosphate to ADP to produce ATP using energy from hydrogen atoms carried by NAD and FAD. Most ATP produced this way.

Question 27

What is the overall equation for aerobic respiration?

Answer 27

C₆H₁₂O₆ +6O₂ —> 6CO₂+6H₂O (+energy)

Question 28

What are the stages of aerobic respiration?

Answer 28

1. Glycolysis- splitting of 6C glucose molecule into two 3C pyruvate molecules.
2. Link reactions- 3C pyruvate enters series of reactions- lead to formation of acetylcoenzyme A- 2C molecule.
3. Krebs cycle- acetylcoenzyme A into cycle of oxidation-reduction reactions- yields ATP and large quantities of reduced NAD and FAD.
4. Oxidative phosphorylation- use of electrons- associated with reduced NAD and FAD- released Krebs cycle to synthesise ATP- water produced as a byproduct.

Question 29

Where do the different stages of respiration occur?

Answer 29

• The first three stages of aerobic respiration are reactions that produce products to be used in the final stage (oxidative phosphorylation) to produce lots of ATP.
• Glycolysis- occurs in cytoplasm. Link reaction, Krebs cycle and oxidative phosphorylation occur in the mitochondria.

Question 30

Describe the adaption of mitochondria for aerobic respiration.

Answer 30

• Mitochondria- only found in eukaryotic cells.
• Bounded by a smooth outer membrane and inner membrane folded into extensions called cristae.
• Inner space- matrix- contains proteins, lipids and DNA.
• The cristae of the mitochondria provide a large surface area to maximise respiration.
• The Krebs cycle and link reaction occur in the matrix.
• Oxidative phosphorylation occurs in the cristae- membrane control enzymes and proteins needed for ATP synthesis.
• There are a greater number of mitochondria in metabolically active cells e.g. muscles, liver cells. Mitochondria also have more densely packed cristae- greater surface are of membrane for incorporating enzymes and other proteins.

Question 31

Describe the effects of mitochondrial disease.

Answer 31

• ATP production can be affected by mitochondrial diseases- which affect mitochondria’s function.
• Diseases- affect how proteins in the Krebs cycle or oxidative phosphorylation function- reduces ATP production.
• This causes anaerobic respiration to increase- lactate produced results in muscle fatigue and weakness and high lactate concentrations in the blood.

Question 32

Describe anaerobic respiration.

Answer 32

• Anaerobic respiration- occurs in the absence of oxygen.
• Doesn’t involve link reaction, Krebs cycle, or oxidative phosphorylation- products of glycolysis converted into ethanol and lactate.

Question 33

What are the stages of anaerobic respiration.

Answer 33

• Glycolysis
• Fermentation

Question 34

What is the equation for anaerobic repiration in plants and yeast?

Answer 34

Glucose —> Ethanol + CO₂ (+energy)

Question 35

What is the equation for anaerobic repiration in humans and mammals?

Answer 35

Glucose —> Lactate (+energy)

Question 36

Describe why anaerobic respiration is neccessary.

Answer 36

• If no oxygen is present, the Krebs cycle and the electron transport chain cannot continue because all the FAD and NAD become reduced as there is no final electron or proton acceptor.
• This means FAD and NAD are unable to take up the H+ produced during the Krebs cycle, so the enzymes stops working.
• Only glycolysis can produce ATP in anaerobic conditions.
• For glycolysis to continue, hydrogen must be constantly removed from the reduced NAD to regenerate NAD. Without this, all the NAD would be reduced, leaving no NAD to take up hydrogen newly produced in glycolysis. This is the process involved in anaerobic respiration.

Question 37

Describe how anaerobic respiration occurs generally speaking.

Answer 37

• Anaerobic respiration mainly involves glycolysis.
• For glycolysis to continue, hydrogen must be constantly removed from the reduced NAD to regenerate NAD. Without this, all the NAD would be reduced, leaving no NAD to take up hydrogen newly produced in glycolysis.
• Regeneration of NAD- achieved by pyruvate oxidising reduced NAD by accepting hydrogen.

Question 38

When is pyruvate converted into ethanol and CO₂?

Answer 38

In anaerobic respiration of certain bacteria and fungi e.g. yeast, and some plants (e.g. waterlogged roots).

Question 39

Describe anaerobic respiration in plants and micro-organisms.

Answer 39

• Pyruvate loses carbon dioxide and accepts hydrogen from reduced NAD, producing ethanol.
• Pyruvate + Reduced NAD –> Ethanol + Carbon dioxide + Oxidised NAD.
• Used for brewing ethanol for e.g. beer.

Question 40

Why is anaerobic respiration unfavourable in plants and fungi?

Answer 40

Ethanol is toxic to most plants and micro-organisms as it inhibits growth and can kill cells.

Question 41

When is pyruvate converted into lactate?

Answer 41

• Anaerobic respiration in animals.
• This is used to overcome a temporary shortage of oxygen e.g. after birth, living in water, intense exercise.
• Exercise- muscles have an oxygen debt- because oxygen used more rapidly than supplied.
• NADH accumulates and needs to be removed.

Question 42

Describe anaerobic respiration in animals?

Answer 42

• As NADH accumulates and needs to be removed pyruvate molecules take up two hydrogen atoms from reduced NAD to form lactate.
• Pyruvate + NADH (reduced NAD)  lactate + NAD (oxidised NAD).
• Lactate is then oxidised back into pyruvate when oxygen is available. The pyruvate can then be further oxidised to release energy or converted into oxygen.

Question 43

Why is lactate production not favourable in animals?

Answer 43

Lactate causes cramp and muscle fatigue if it accumulates in muscle tissues as it forms acid. It changes the pH affecting enzymes. It is therefore important to remove lactate by the blood to be taken up by the liver to be converted into glycogen, although some muscles sometimes have tolerance to lactate.

Question 44

Why does anaerobic respiration only involve glycolysis?

Answer 44

As pyruvate is converted to either ethanol or lactate it is not available for the Krebs cycle- so it cannot occur and neither can the electron transfer chain. ATP can only be formed by glycolysis.

Question 45

What is glycolysis- describe it’s features.

Answer 45

• First stage of aerobic and anaerobic respiration.
• Occurs in cytoplasm- enzymes for process all in cytoplasm so no organelle or membrane required for it to take place.
• Doesn’t require oxygen- anaerobic process.
• Universal- provides indirect evidence for evolution.
• Series of small enzyme-controlled reactions.
• The process in which hexose (usually glucose- 6 carbon sugar) is split into two molecules of pyruvate (3 carbons).

Question 46

Describe the steps of glycolysis.

Answer 46

1. Phosphorylation of glucose to glucose phosphate adding two phosphate molecules using the hydrolysis of two ATP molecules. This makes the molecule more reactive, and lowers the activation energy for the following reactions.
2. Each glucose phosphate molecule is split in two triose phosphate (3-carbon molecules).
3. Hydrogen is removed from each triose phosphate- it is oxidised to form pyruvate (a three carbon molecule). Hydrogen is transferred to reduce NAD into reduced NAD. In the process, four molecules of ATP are produced from ADP, with a net gain of 2 ATP as 2 ATP were used at the start of the process.

Question 47

Draw a diagram to represent glycolysis.

Answer 47

Answer on revision card.

Question 48

What are the products of glycolysis?

Answer 48

• 2 molecules of ATP (produced four molecules but two are used in phosphorylation of glucose- net increase is two)- used for energy.
• 2 molecules of reduced NAD- used for oxidative phosphorylation.
• 2 molecules of pyruvate- actively transported into mitochondrial matrix for the link reaction.

Question 49

What are the uses of pyruvate produced in glycolysis?

Answer 49

• If respiration is aerobic, pyruvate from glycolysis enters the mitochondrial matrix by active transport it is then used in the link reaction.
• If respiration is anaerobic, pyruvate can be converted to ethanol or lactate to convert reduced NAD to oxidised NAD to enable glycolysis to continue.

Question 50

Describe the energy yield of glycolysis.

Answer 50

Glycolysis yields only a small amount of energy stored in the glucose molecule. To release the remaining energy, oxygen is used to break down pyruvate further and further release its energy.

Question 51

How many times do the link reaction and Krebs cycle occur?

Answer 51

Two molecules of pyruvate are produced for every glucose molecule that enters glycolysis. This means the link reaction and Krebs cycle occur twice for every glucose molecule.

Question 52

Why is the link reaction important?

Answer 52

• Pyruvate produced during glycolysis possesses potential energy that is released in the Krebs cycle.
• Before the pyruvate can enter the Krebs cycle, it must be oxidised in the link reaction.

Question 53

Where does the link reaction occur?

Answer 53

In the matrix of the mitochondria.

Question 54

Describe the link reaction.

Answer 54

• Pyruvate molecules produced in the cytoplasm during glycolysis- actively transported into the matrix of mitochondria- undergoes series of reactions.
• Pyruvate is decarboxylated and oxidised to acetate (2-carbon molecule)- loses a carbon dioxide molecule and two hydrogens- taken up by NAD- forms reduced NAD.
• Acetate combines with coenzyme A (CoA) to produce acetylcoenzyme A.

Question 55

What is the equation for the link reaction?

Answer 55

Pyruvate + NAD + CoA  acetyl CoA + reduced NAD + CO2

Question 56

What are the products of the link reaction?

Answer 56

• 2 acetylcoenzyme A- to the Krebs cycle.
• 2 carbon dioxide- released as waste product.
• 2 reduced NAD- goes to oxidative phosphorylation.

Question 57

Describe the features of the Krebs cycle.

Answer 57

• Occurs in the matrix of the mitochondria.
• The cycle occurs twice for every glucose molecule (as each glucose produces two acetyl CoA).
• It involves a series of oxidation-reduction reactions to produce the coenzymes FAD and NAD and ATP by substrate-level phosphorylation.

Question 58

Describe the process of the Krebs Cycle.

5 steps

Answer 58

1. Acetylcoenzyme A (2-carbon) from link reaction combines with the 4-carbon molecule-oxaloacetate to produce a 6-carbon molecule- citrate which enters the Krebs cycle.
2. Coenzyme A goes back to the link reaction to be used again.
3. The 6-carbon molecule- citrate is converted to a 5 carbon molecule through decarboxylation- carbon dioxide is removed. Dehydrogenation also occurs and the hydrogen is used to reduce NAD to reduced NAD.
4. The 5-carbon molecule is then converted to a 4-carbon molecule- oxaloacetate- by decarboxylation and dehydrogenation also occurs producing one molecule of reduced FAD and two molecules of reduced NAD. One molecule of ATP is produced by direct transfer of a phosphate group to ADP through substrate-level phosphorylation.
5. 4-carbon molecule- oxaloacetate- combine with new molecule of acetylcoenzyme A to begin the cycle gain.

Question 59

What are hte products of the Krebs cycle (per molecule of pyruvate)

Answer 59

• Reduced coenzymes- NAD and FAD- used in oxidative phosphorylation.
• Coenzyme A- reused in link reaction.
• Oxaloacetate- regenerated for use in next Krebs cycle.
• Two carbon dioxide- released as waste.
• 3 reduced NAD- oxidative phosphorylation.
• 1 reduced FAD- oxidative phosphorylation
• One molecule of ATP- used for energy.

Question 60

What are the importance of the first three steps of aerobic respiration.

Answer 60

• The previous steps of aerobic respiration of glucose produce hydrogen atoms.
• Hydrogen atoms- valuable source of potential energy- carried coenzymes reduced NAD and FAD to oxidative phosphorylation.
• Electrons within hydrogen atoms- used as a source of energy to produce ATP in oxidative phosphorylation- provided by coenzymes.

Question 61

Describe the features of oxidative phosphorylation.

Answer 61

• Oxidative phosphorylation occurs in mitochondria.
• Also known as the chemiosmotic theory of oxidative phosphorylation.
• Oxidative phosphorylation involves the electron transfer chain- electrons are transferred through a series of electron carrier molecules.
• Like photosynthesis respiration relies on chemiosmosis- ATP synthesis occurs when protons diffuse down an electrochemical gradient through the enzyme ATP synthase, embedded in the inner mitochondrial membranes of cellular organisms. ATP synthase catalyses ATP synthesis.

Question 62

Describe the process of oxidative phosphorylation.

Hint: 6 steps

Answer 62

1. Hydrogen atoms are released from reduced NAD and FAD (they’re oxidised). Hydrogen ions split into protons and electrons. Electrons are donated the first molecule in the electron transfer chain.
2. Electrons pass along a chain of electron transfer carrier molecules in a series of oxidation-reduction reactions, losing energy at each protein.
3. The energy they release as they flow along the chain enables the active transport of protons from the matrix across the inner mitochondrial membrane to the inter-membranal space.
4. The concentration of protons in the intermembrane space is higher than in the mitochondrial matrix- this forms an electrochemical gradient.
5. Chemiosmosis occurs- The protons diffuse down the electrochemical gradient through ATP synthase embedded in the inner mitochondrial membrane. This drives the synthesis of ATP from ADP and Pi.
6. At the end of the chain, in the mitochondrial matrix, electrons combine with protons and oxygen to form water- oxygen is the final acceptor of electrons.

Question 63

Why is oxygen important in oxidative phosphorylation.

Answer 63

Oxygen is important as the final acceptor of hydrogen atoms produced during glycolysis and the Krebs cycle- without it hydrogen ions and electrons would move back along the chain and respiration would stop.

Question 64

Describe how respiration ensures efficient energy transfer.

Answer 64

• If energy is released in a single step- more of it released as heat and less stored for useful purposes.
• Therefore, in respiration released a little at a time in stages- more can be stored to benefit the organism.
• Electrons carried by NAD and FAD are not transferred in one step- instead passed along a series of electron transfer carrier molecules- each has a slightly lower energy level.
• Electrons -move down energy gradient- this allows their energy to be released gradually so the process is more efficient.

Question 65

How much ATP does aerobic respiration produce per glucose?

Answer 65

32

Question 66

How much ATP does anaerobic respiration produce per glucose?

Answer 66

2

Question 67

What is the effect of increased respiration?

Answer 67

• More pyruvate is produced by glycolysis.
• More acetylcoenzyme A enters the Krebs cycle from the link reaction.
• The Krebs cycle generates more reduced coenzymes.
• More reduced coenzymes pass their electrons to the electron transfer chain.
• **More ATP is produced. **

Question 68

Describe the role of other substrates in producing ATP?

Answer 68

• Glucose- used as a respiratory substrate in aerobic and anaerobic respiration.
• Other respiratory substrates can be used to provide energy to produce ATP in aerobic respiration- lipids and protiens can be converted into molecules able to enter the Krebs cycle. These molecules can be oxidised to release energy.
• Other respiratory substrates enter the Krebs cycle to release their stored energy to produce ATP.

Question 69

Describe how ATP is generated from lipids in aerobic respiration.

Answer 69

• Lipids- hydrolysed to glycerol and fatty acids.
• Glycerol- phosphorylated- converted into triose phosphate- enters glycolysis and the Krebs cycle.
• Fatty acids- broken down into 2 carbon fragments- oxidised- converted to acetyl coenzyme A- enters the Krebs cycle.
• Produces 2-carbon fragments of carbohydrate and many hydrogen atoms.
• Hydrogen atoms- used to produce ATP during oxidative phosphorylation- lipids- release double the energy for the same ass of carbohydrate.

Question 70

Describe how ATP is generated from proteins in aerobic respiration.

Answer 70

• First hydrolysed to amino acids- have amino group removed before entering the respiratory pathway at different points depending on carbon atoms they contain.
• 3C compounds- converted to pyruvate.
• 4C and 5C- converted into intermediates for Krebs cycle.

Question 71

How can respiration rate be measured?

Answer 71

• Measuring the CO2 volume increase.
• Redox indicator e.g. DCPIP/ methylene blue could be used to investigate dehydrogenase activity (in reducing NAD and FAD).
• Using a respirometer to measure differences in oxygen volumes.
• Yeast- both aerobic and anaerobic respiration produce CO2- rate of production gives indication of respiration rate- measured using a gas syringe.

Question 72

When given a question about respiration experiments what must you remember?

Answer 72

Always mention the type of respiration.

Question 73

How would you investigate the effect of a named variable on the rate of aerobic respiration of cultures of single-celled organisms.

Hint: 7 steps

Answer 73

• Put a known volume and concentration of substrate solution (e.g. glucose) into a test tube and add a set volume buffer solution to keep pH constant (choose the optimum pH for the yeast).
• Place the test tube in a water bath set to the temperature investigated. Leave it for the temperature of the substrate to be stabilised.
• Add a known mass of dried yeast and stir for two minutes.
• After the yeast has dissolved, attach a bung and gas syringe set to zero to the test tube.
• Start the stopwatch as soon as the bung has been added, and at regular intervals e.g. each minute, record the increase in volume present in the gas tube- do this for a set time e.g. 10 minutes.
• Set up a negative control where no yeast is present- ensure that no CO2 is produced without yeast.
• Repeat three times and find the mean rate of CO2 production.

Question 74

How would you investigate the effect of a named variable on the rate of anaerobic respiration of cultures of single-celled organisms.

Answer 74

• Put a known volume and concentration of substrate solution (e.g. glucose) into a test tube and add a set volume buffer solution to keep pH constant (choose the optimum pH for the yeast).
• Place the test tube in a water bath set to the temperature investigated. Leave it for the temperature of the substrate to be stabilised.
• Add a known mass of dried yeast and stir for two minutes.
• Add liquid paraffin into the test tube so that it covers the surface of the solution- this will stop oxygen entering. Leave it for a set time so that all remaining oxygen is used.
• Attach a bung and gas syringe set to zero to the test tube.
• Start the stopwatch as soon as the bung has been added, and at regular intervals e.g. each minute, record the volume present in the gas tube- do this for a set time e.g. 10 minutes.
• Set up a negative control where no yeast is present- ensure that no CO2 is produced without yeast.
• Repeat three times and find the mean rate of CO2 production.

Question 75

What factors could you investigate in investigating factors affecting respiration in single-celled organisms and what should you remember with these factors?

Answer 75

• Temperature
• Substrate concentration.
• Different types of substrates.
• Only one variable (the independent variable) should be changed at a time. Other variables could affect the results so need to be controlled to keep the results valid.

Question 76

How does increased temperature affect the rate of respiration?

Answer 76

Increased temperature should result in a higher rate of carbon dioxide production and therefore respiration as enzymes work faster.

Question 77

How do you use a respirometer to measure oxygen consumption in multicellular organisms?

Hint: 11 steps.

Answer 77

• Respirometers indicate the rate of aerobic respiration- measure amount of oxygen consumed by an organism over a period of time. It can be used to measure the respiration rate of woodlice or other small organisms such as plants.
• The apparatus involves two tubes with bungs. In the tubes are gauze above potassium hydroxide solution where the woodlice/ beads sit. One bung has a syringe attached and the other has a tap. Attached to both bungs between the tubes is a manometer (a capillary tube filled with a coloured fluid, with a scale).
• Set up the apparatus partially submerged in a water bath at 15°C to provide optimum temperature for the enzymes responsible for respiration in woodlice.
• Set up a control tube in the same way as the apparatus but substitute the woodlice for glass beads of the same mass.
• Leave the tap open for ten minutes and remove the syringe to allow the apparatus to reach equilibrium- accounting for pressure changes and the respiration rate of the organism to stabilise.
• Close the syringe and shut the tap.
• Use the syringe to reset the manometer so the ends of the fluid are the same level each side- record the reading on the syringe.
• As respiration occurs, the volume of the air in the test-tube will decrease due to oxygen consumption during respiration and CO2 absorbed by potassium hydroxide.
• The decreased volume will reduce the pressure in the tube- caused the fluid in the capillary tube to move towards it.
• Leave the apparatus for a set period e.g. ten minutes. Use the syringe to reset the manometer to equal level on both sides. The syringes volume is recorded again. The difference between the figure is the oxygen consumption- used to calculate the rate of respiration.
• Repeat to calculate the mean volume of O2.