Respiration

Question 1

Why Do We Need Respiration?

Answer 1

Glucose cannot be used directly by cells as a source of energy and so cells use ATP as their mediate energy source.

The formation of ATP happens via the breakdown of glucose.

This takes place during the process of cellular respiration.

Question 2

What Is Respiration?

Answer 2

The formation of ATP from the breakdown of glucose.

There are two types of cellular respiration:

• Aerobic respiration,
• Anaerobic respiration.

Formula for respiration:

Glucose + Oxygen —> Water + Carbon Dioxide + ATP.

C6H12O6 + 6O2 —> 6H2O + 6CO2 (+ATP).

Question 3

What Is Aerobic Respiration?

Answer 3

Aerobic respiration is a type of cellular respiration.

It requires oxygen and produces carbon dioxide, water and a lot of ATP.

Question 4

Anaerobic Respiration?

Answer 4

Anaerobic respiration is a type of cellular respiration.

It takes place in the absence of oxygen and produces lactate (in animals) or ethanol and carbon dioxide (in plants and fungi).

BUT only a little ATP is produced in both cases.

Question 5

Stages Of Aerobic Respiration?

Answer 5

Glycolysis,

Link reaction,

Krebs cycle,

Oxidative phosphorylation.

Question 6

Glycolysis Steps?

Answer 6

Glycolysis is the initial stage of both aerobic and anaerobic respiration.

It occurs in the cytoplasm of all living cells.

This stage basically takes glucose (a sugar) and oxidises it to pyruvate (an acid).

1. Glucose is phosphorylated by the addition of two phosphate molecules (made more reactive). The phosphate molecules come from the hydrolysis of 2x ATP molecules to ADP. This provides the energy to turn glucose to phosphorylated glucose and lowers the activation energy for the enzyme controlled reactions that follow.
2. Each phosphorylated glucose is split into two 3-carbon molecules known as triose phosphate.
3. Hydrogen is removed from each of the two triose phosphate molecules (so it’s oxidised) and transferred to a hydrogen-carrier molecule known as NAD to form reduced NAD.
4. Enzyme-controlled reactions convert each triode phosphate into another 3-carbon molecule called pyruvate. In this process, two molecules of ATP are re-generated from ADP.

4x ATP are produced (but 2 molecules are used at the start so the ‘net profit’ is 2x ATP).
2x molecules of reduced NAD.
2x molecules of pyruvate.

Question 7

Energy Yields From Glycolysis?

Answer 7

The overall yield (profit) from one glucose molecule undergoing glycolysis is:

• 4x ATP are produced (but 2 molecules are used at the start so the ‘net profit’ is 2x ATP).
• 2x molecules of reduced NAD.
• 2x molecules of pyruvate.

Question 8

How Is Glycolysis Used As Evidence For Evolution?

Answer 8

Glycolysis is a universal feature of every living organism and therefore provides indirect evidence for evolution.

Because it is used in every living organism, it shows how we have developed from one ‘thing’ (stage).

Question 9

Why Does Glycolysis Not Require An Organelle?

Answer 9

The enzymes involved in the glycolytic pathway are found in the cytoplasm of cells and so glycolysis does not require any organelle or membrane for it to take place.

Question 10

Link Reaction Steps?

Answer 10

The pyruvate molecules produced in glycolysis possess potential energy that can only be released in the Krebs cycle.

Before pyruvate can enter the Krebs cycle, the pyruvate molecules must first be oxidised in the link reaction.

Link reactions takes place in mitochondria.

1. The pyruvate molecules produced in cytoplasm by glycolysis are actively transported into the matrix of the mitochondria.
2. The 3-carbon pyruvate looses a carbon dioxide molecule and two hydrogens (pyruvate is oxidised). This forms a 2-carbon molecule called acetate. The hydrogens are accepted by the NAD to form reduced NAD.
3. Acetate combines with a molecule called coenzyme A (CoA) to produce a compound called acetylcoenzyme A.

Overall Equation:

Pyruvate + NAD + CoA —> acetyl CoA + R.NAD + CO2.

Question 11

Krebs Cycle Steps?

Answer 11

The Krebs cycle was named after the British biochemist, Hans Krebs, who worked it out.

The Krebs cycle involves a series of oxidation-reduction reactions that take place in the matrix of mitochondria.

1. AcetylcoenzymeA splits to form Acetyl and CoA.
   The 2-carbon acetyl combines with a 4-carbon molecule (oxaloacetate) to produce a 6-carbon molecule (citrate).
2. In a series of reactions, this six-carbon molecule (citrate) is decarboxylated and dehydrogenated to form a 5-carbon molecule. This CO2 is released into matrix and hydrogen picked up by NAD to form reduced NAD.
3. The 5-carbon compound is then dehydrogenated and decarboxylated again. The hydrogen is taken by the NAD which makes reduced NAD and the carbon dioxide is released into matrix.
4. The 4-carbon molecule temporarily combines with a new molecule of coenzyme A. Because of this re-arrangement of molecules, one molecule of ATP is produced from ADP and Pi (substrate-level phosphorylation, basically condensation reaction of ADP-Pi).
5. The 4-carbon molecule then loses the CoA (because that was a temporary binding) and is dehydrogenated (reduced) to form another 4-carbon molecule called oxaloacatate. The FAD picks up this hydrogen to form reduced FAD.
6. The new 4-carbon molecule is then dehydrogenated again for form another 4-carbon molecule. The hydrogen is taken by NAD this time to produced reduced NAD. An isomerism step (catalysed by isomerase enzyme) also occurs here in order to produce oxaloacatate.
7. The oxaloacatate can now combine with a new molecule of acetylcoenzyme A to begin again.

By the end of this cycle, you have:

• 1x molecule of ATP,
• 2x molecules of CO2,
• 1x FAD,
• 3x NAD.

Question 12

Products Of Krebs Cycle?

Answer 12

For each molecule of pyruvate, the Krebs cycle produces:

• Reduced coenzymes such as NAD and FAD (these have the potential to provide energy to produce ATP molecules by oxidative phosphorylation).
• One molecule of ATP.
• Three molecules of carbon dioxide.

(2x pyruvate molecules are produced for each original glucose molecule, therefore, a single glucose molecule means the quantities above are doubled).

Question 13

Phosphorylated Glucose Is Also Called?

Answer 13

Hexose Bisphospahte.

Question 14

How Does A Pyruvate Molecule Get Into The Matrix?

Answer 14

It is actively transported.

Pyruvate is made in the cytosol (cytoplasm) by glycolysis.

It travels through the outer membrane of the mitochondria through a channel.

It then travels though the inner membrane via a H+/Pyruvate Symporter to reach the matrix.

Question 15

Coenzymes?

Answer 15

Co-enzymes are not enzymes.

They are molecules that some enzymes require in order to function.

Co-enzymes play a major role in photosynthesis and respiration, where they carry hydrogen atoms from one molecule to another.

Examples include: NAD, FAD, NADP.

In respiration, NAD is the most important carrier. It works with dehydrogenase enzymes.

Dehydrogenase enzymes catalyse the removal of hydrogen atoms from substrates and transfer them to other molecules involved in oxidative phosphorylation.

Question 16

The Importance Of The Krebs Cycle?

Answer 16

The Krebs cycle performs an important role in the cells of organisms for four reasons:

1. It breaks down macromolecules into smaller ones (e.g. pyruvate is broken down into carbon dioxide).
2. It produces hydrogen atoms (that are carried by NAD) to the electron transfer chain and provides energy for oxidative phosphorylation. This leads to the production of ATP that provides a metabolic energy for the cell.
3. It regenerates the four carbon molecule that combines with a set tile coenzyme A, which would otherwise accumulate.
4. It is a source of intermediate compounds used by cells in the manufacture of other important substances such as fatty acids, amino acids and chlorophyll.

Question 17

What Happens To Carbon Dioxide And Hydrogen Atoms In The Matrix?

Answer 17

Carbon dioxide is a waste product.

It is removed via gaseous exchange.

Hydrogen atoms (or more particularly, the electrons they possess) are valuable as a potential source of energy.

These hydrogen atoms are carried by the co-enzymes NAD and FAD into the stage of aerobic respiration, oxidative phosphorylation.

Question 18

Oxidation Phosphorylation In Relation To Mitochondria?

Answer 18

Mitochondria are organelles that are found in eukaryotic cells.

Each mitochondrion is bounded by a smooth outer membrane and an inner one that is folded into extension is called cristae.

The inner space, or matrix, of the mitochondrion consists of protein lipids and traces of DNA.

Mitochondria are the site of oxidative phosphorylation.

Within the inner folded membrane (cristae) are the enzymes and other proteins involved in oxidative phosphorylation and hence, ATP synthesis.

Question 19

Adaptations Of Mitochondria Which Aid In Respiration?

Answer 19

Mitochondria play a huge role in respiration and so there are greater numbers of mitochondria in metabolically active cells, such as muscles, the liver and epithelial cells (which carry out active transport).

The mitochondria in these cells also have more densely packed cristea which provide a greater surface area of membrane incorporating enzymes and other proteins involved in oxidative phosphorylation.

Question 20

Where Does Oxidative Phosphorylation Occur?

Answer 20

Both reactions (chemiosmosis and electron transport chain) occur on the inner membrane of the mitochondria.

The inner membrane is covered in ATPase enzymes which are required for oxidative phosphorylation.

The inner membrane is folded many times so we can fit as many as these enzymes on the membrane as possible, therefore, the maximum amount of reactions occurring.

Question 21

Oxidative Phosphorylation Steps: Electron Transport Chain?

Answer 21

1. NADH (reduced NAD) and FADH2 (reduced FAD - and yes, the 2 is supposed to be there future Hav) are both oxidised back to NAD and FAD.
2. When these molecules (NADH and FADH2) are oxidised, they release electrons and their hydrogens that they were carrying.
3. The electron carriers on the inner membrane accept these electrons. The electrons move down from carrier A to carrier B to carrier C. The electrons provide energy to the carriers to allow the hydrogens (protons) in the matrix to be pumped across the inner mitochondrial membrane via the carriers, into the inter-membrane space (active transport).
4. Once the electrons react carrier C (cytochrome oxidase), oxygen (the final electron acceptor) combines with the electron and 2x hydrogens in the matrix to make water molecules.
5. Now, there is a large electrochemical gradient (many protons in the inter-membrane space). This is when chemiosmosis occurs.

Question 22

Oxidative Phosphorylation Steps: Chemiosmosis?

Answer 22

1. There is a high concentration of protons in the inter-membrane space. This has created a large electrochemical gradient.
2. The hydrogens (protons) move down their electrochemical gradient through an enzyme called the ATP synthase enzyme which is embedded along the inter mitochondrial membrane
3. The protons provide the enzyme energy to synthesis ATP from ADP and Pi molecules.

There are between 26-32 molecules of ATP produced for every 1 glucose.

Question 23

For Every Glucose Molecule…

Answer 23

Glycolysis produces - 2x NADH and 2x ATP,

Link reaction produces - 2x NADH,

Krebs Cycle produces 2x FADH2, 6x NADH, 2x ATP (remember, this cycle turns twice so in one turn of the Krebs cycle, the amounts above must be halved),

Oxidative Phosphorylation produces - 26-32 ATP.

Question 24

Why Is It More Efficient Sending Electrons Down The Transport Chain, Carrier By Carrier?

Answer 24

In general, the greater the energy that is released in a single step, the more of it is released as heat and therefore, there is less available for more useful purposes.

For this reason, the electrons carried by NAD and FAD are not transferred in one step.

Instead, they are passed along a series of electron transfer carrier molecules, each of which is that a slightly lower energy level.

The electrons therefore moved down and energy gradient.

The transfer of electrons down this gradient allows their energy to release gradually and therefore more usefully

Question 25

Alternative Respiratory Substrates?

Answer 25

Sugars are not the only substances which can be oxidised by cells to release energy. Lipids and proteins may, in certain circumstances, be used as respiratory substrates.

Question 26

RQ?

Answer 26

RQ stands for the respiratory quotient. Calculation: RQ = CO2 produced / O2 Consumed. E.g. glucose: C6H12O6 + 6O2 -> 6H2O + 6CO2. You can compare the RQ using formula from different respiratory substrates (from lipids, proteins or glucose by using their formula).

Question 27

How Can You Measure Rate Of Respiration?

Answer 27

Measure uptake of reactants or production of products. E.g. measure the amount of CO2 given off by an animal.

Question 28

Respiration Of Lipids?

Answer 28

Before being respired, lipids are first hydrolysed to glycerol and fatty acids. The glycerol is then phosphorylated and converted to triose phosphate which enters the glycolysis pathway and then the Krebs cycle. The fatty acid component is broken down into 2-carbon fragments which are converted to a acetyl-coenzyme A. This then enters the Krebs cycle. The oxidation of lipids produces 2-carbon fragments of carbohydrate and many hydrogen atoms. The hydrogen atoms are used to produce ATP during oxidative phosphorylation. Lipids release more than double the energy of the same mass of carbohydrate.

Question 29

Respiration Of Protiens?

Answer 29

Protiens are used for respiration when there are too many amino acids in the body or in a state of starvation (the body will break down muscle for protein to use in respiration). Protein is first hydrolysed to amino acids. Then, the amino acids have their amino group removed (deamination) before entering the respiratory pathway at different points, depending on the number of carbon atoms they contain. 3-carbon compounds are converted to pyruvate, while 4- and 5-carbon compounds are converted to intermediate in the Krebs cycle.

Question 30

What Cycle Can Occur During Anaerobic Respiration?

Answer 30

Glycolysis. This is because, in the other cycles, there is no FAD or NAD available to take up H+ produced during the Krebs cycle (so enzymes stop working) because the FAD and NAD will all be reduced without oxygen.

Question 31

What Anaerobic Respiration Occurs In Eukaryotic Cells?

Answer 31

In plants (and microorganisms such as yeast) ethanol and carbon dioxide is produced from pyruvate(after glycolysis). In animals, the pyruvate is converted to lactate.

Question 32

Production Of Ethanol In Plants?

Answer 32

Occurs in plants, fungi and bacteria. This is called alcoholic fermentation. It can also occur in some cells of higher plants, for example, root cells under waterlogged conditions. The pyruvate molecule formed at the end of my glycolysis loses a molecule of carbon dioxide and accepts hydrogen from reduced NAD to produce ethanol. Equation: Pyruvate + Reduced NAD —> Ethanol + Carbon Dioxide + Oxidised NAD. This form of anaerobic respiration in yeast has been exploited by humans for thousands of years in the brewing industry. Yeast is grown in anaerobic conditions in which its ferments natural carbohydrate implant products, such as grapes (wine production) or barley seeds (beer production) into ethanol.

Question 33

Production Of Lactate In Animals?

Answer 33

Anaerobic respiration leading to the production of lactate occurs in animals. Lactate production occurs most commonly in muscles as a result of extraneous exercise. In these conditions, oxygen may be used up more rapidly than it can be supplied and therefore an oxygen debt occurs. When oxygen is in short supply, NAD from glycolysis can accumulate and must be removed. To achieve this, each pyruvate molecules produced takes up the two hydrogen atoms from the reduced NAD produced in glycolysis to form lactate as shown in the equation: Pyruvate + Reduced NAD —> Lactate + Oxidised NAD. When oxygen is available again, the lactate produced is oxidised back to pyruvate. This can then be either further oxidised to release ATP or converted into glycogen. This is called lactate fermentation.

Question 34

Problems With Lactate?

Answer 34

Lactate can cause cramp and muscle fatigue if it is allowed to accumulate in the muscle tissue. Lactate is an acid so it also causes pH changes which affects enzymes. The lactate is removed from the muscles by the blood and taken to the liver to be converted to glycogen.

Question 35

Energy Yields From Anaerobic/Aerobic Respiration?

Answer 35

ATP is made in aerobic respiration in: - substrate-level phosphorylation in glycolysis and Krebs cycle. This is direct linking of Pi from a respiratory intermediate to ADP. - oxidative phosphorylation in the electron transfer chain. This is indirect linking of Pi to ADP involving energy from hydrogen atoms that are carrier on NAD and FAD. ATP in anaerobic respiration: - In anaerobic respiration, pyruvate is converted to ethanol all lactate. The only ATP that can be produced by anaerobic respiration is formed by glycolysis.

Question 36

Practical: investigating factors effecting aerobic respiration in single-called organisms?

Answer 36

Yeast are single celled organisms that can grow in culture. They can respire aerobically and anaerobically. The method below shows you how to investigate the effect of temperature on yeast aerobic respiration. You will need to decide what temperatures you’re going to investigate before you start (e.g. 10°, 20°). How: 1. Put a known volume and concentration of substrate solution (e.g. glucose) in a test tube. Add a known volume of buffer solution to keep the pH constant. For yeast this is 4-6. 2. Place the test tube in a water bath set to one of the temperatures being investigated. Leave it there for 10 minutes to allow the temperature of the substrate to stabilise. 3. Add a known mass of dried yeast to the test tube and stay for two minutes. 4. After the yeast has dissolved into the solution, put a bum with a tube attached to a gas syringe in the top of the test tube. The gas syringe should be set to 0. 5. Start a stopwatch is it soon as the bung has been put in the test tube. 6. As the yeast respire, the CO2 formed will travel up the tube and into the gas syringe, which is used to measure the volume of CO2. 7. At regular time intervals (e.g. every minute) record the volume of CO2 that is present in the gas syringe. Do this for a set amount of time (e.g. 10 minutes). 8. A controlled experiment should also be set up at each temperature, where no use is present. No CO2 should be formed without the yeast. 9. Repeat the experiment 3 times at each temperature you’re investigating. Use your data to calculate the mean rate of CO2 production at each temperature. The yeast will only respire aerobically until the oxygen trapped in the test tube is all used up. If you wanted to run the experiment for more time or with more yeast or glucose, you could use a conical flask instead of a test tube that can trap more oxygen.

Question 37

Practical: investigating factors effecting anaerobic respiration in single-called organisms?

Answer 37

The method below shows you how to investigate the effect of temperature on yeast anaerobic respiration. You will need to decide what temperatures you’re going to investigate before you start (e.g. 10°, 20°). SAME AS AEROBIC PRACTICAL BUT YOU USE LIQUID PARAFFIN AFTER STEP 3. How: 1. Put a known volume and concentration of substrate solution (e.g. glucose) in a test tube. Add a known volume of buffer solution to keep the pH constant. For yeast this is 4-6. 2. Place the test tube in a water bath set to one of the temperatures being investigated. Leave it there for 10 minutes to allow the temperature of the substrate to stabilise. 3. Add a known mass of dried yeast to the test tube and stay for two minutes. 4. After the east has dissolved into the substrate solution, trickle some liquid paraffin down the inside of the test tube so that it settles on and completely covers the surface of the solution. This will stop oxygen getting in, which will force they used to respire anaerobically. 5. Put a bong, with a tube attached to a gas syringe, in the top of the test tube. The gas syringe should be set to 0. Start a stopwatch is it soon as the bung has been put in the test tube. 6. As the yeast respire, the CO2 formed will travel up the tube and into the gas syringe, which is used to measure the volume of CO2. 7. At regular time intervals (e.g. every minute) record the volume of CO2 that is present in the gas syringe. Do this for a set amount of time (e.g. 10 minutes). 8. A controlled experiment should also be set up at each temperature, where no use is present. No CO2 should be formed without the yeast. 9. Repeat the experiment 3 times at each temperature you’re investigating. Use your data to calculate the mean rate of CO2 production at each temperature.

Question 38

Practical: using a respirometer?

Answer 38

Respirometers can be used to indicate the rate of aerobic respiration by measuring the amount of oxygen consumed by an organism over a period of time. The example below shows have a respirometer can be used to measure the respiration rate of woodlice. You can also use it to measure the respiration rate of other small organisms or of plant seeds. Apparatus: 1. Test tube with potassium hydroxide solution, gauze, cotton wool and wood lice in. 2. A bung attached to ^ that test tube with a gas syringe attached. 3. A manometer attached to the test tube ^ as well (two holes in bung). 4. Mono meter connected to another test tube with two bung hole too. The second bung hole has a closed tap attached. 5. This test tube should contain potassium hydroxide solution, cotton wool, gauze and glass beads (this is the control). 6. The whole apparatus should be kept in a 15°C waterbath to provide the optimum temperature for the woodlice and therefore the optimum temperature for the enzymes involved in respiration.

Question 39

Practical: using a respirometer - step by step?

Answer 39

1. Set the apparatus up and place into a water bath at 15°C. The glass beads and the woodlice should have the same mass. 2. For 10 minutes, the tap is left open and the syringe is removed to allow the apparatus to equilibrate (accounting for any expansion that might cause the pressure to change inside) And the respiration rate of the woodlice to stabilise in their new environment. 3. When the 10 minute is up, the tap is closed and the syringe is attached. 4. The syringe is used to reset the monometer, so that the ends of the fluid are at the same level on either side of the ‘U’ and the reading from the volume scale on the syringe (usually in cm3) is recorded. 5. As respiration occurs, the volume of the air in the test tube containing woodlice will decrease, due to the oxygen consumed during respiration. All of the CO2 produced is absorbed by the potassium hydroxide. 6. The decrease in the volume of air will reduce the pressure in the test tube, causing the coloured fluid in the capillary tube of the monometer to move towards the test tube with wood lice. 7. After leaving the apparatus to run for a set period of time (e.g. 10 minutes), the syringe is used to reset the monometer and the reading on the syringes volume scale is recorded again. The difference between this figure and a figure taken at the start of the experiment is the oxygen consumption for this time period. 8. You can use this to calculate a rate of respiration. To check the precision of the result, the experiment is repeated and mean volume of O2 is calculated.

Question 40

Rate equation?

Answer 40

Distance / time. Give units in units you used in calculation. E.g. cm/s or m/s. Always use seconds tho.