Module 5: Respiration

Question 1

Why is energy important and give examples for plants, animals and microorganisms?

Answer 1

Living things need biological processes to occur:

Plants need energy for photosynthesis, active transport, DNA replication and cell division.

Animals need energy for things like muscle contraction, maintenance of body temperature, active transport, DNA replication and cell division.

Microorganisms need energy for things like DNA replication, cell division, protein synthesis and sometimes motility.

Question 2

Describe the structure of the mitochondria.

Answer 2

Mitochondrial DNA.

Mitochondrial matrix.

Outer/inner mitochondrial membrane.

Crista (fold)

Question 3

What is a coenzyme?

Answer 3

It is a molecule that aids the function of an enzyme by transferring a chemical group from one molecule to another.

Question 4

What are the coenzymes used in respiration?

Answer 4

NAD- transfers hydrogen from one molecule to another.

Coenzyme A -transfers acetate between molecules.

FAD - transfers hydrogen from one molecule to another

Question 5

What are the 4 stages of Aerobic respiration?

Answer 5

Glycolysis

The link reaction

The Krebs cycle

Oxidative phosphorylation.

Question 6

What happens in Glycolysis?

Answer 6

This takes place in the cytoplasm.
Glycolysis converts glucose into pyruvate. This process doesn’t require oxygen, so it is an anaerobic process and involved in both aerobic and anaerobic pathways.

1) Glucose is phosphorylated by adding a phosphate from a molecule of ATP. This creates one molecule of hexose phosphate and ADP.
Hexose phosphate is phosphorylated by ATP to form hexose bisphosphate and another molecule of ADP. Due to instability, this 6 carbon compound splits into a 2x 3C compound called triose phosphate.

An inorganic phosphate joins onto the 2x triose phosphate to make 2x triose bisphosphate.

2) Triose bisphosphate is oxidised and loses 2 hydrogens to form 2 molecules of pyruvate. The coenzyme NAD (x2) collects the hydrogen ions, forming 2 reduced NAD

4 ATP are produced, but 2 were used up so therefore there is a net gain of 2 ATP.

Question 7

What are the products of glycolysis?

Answer 7

2 reduced NAD - goes to oxidative phosphorylation.

2 pyruvate - goes to the link reaction

2 ATP (net gain) - used for energy.

Question 8

Describe the process of the link reaction.

Answer 8

Pyruvate is actively transported into the matrix of the mitochondria where the links reaction converts pyruvate into acetyl coenzyme A.

1) firstly pyruvate 3C is decarboxylated. One carbon is removed in the form of carbon dioxide.

2) NAD is reduced to NADH- it collects hydrogen from pyruvate. This converts pyruvate into acetate.

3) Then acetate is combined with coenzyme A (CoA) to form acetyl coenzyme A.

No ATP is produced in this reaction.

Question 9

What are the products of the link reaction?

Answer 9

2 acetyl coenzyme A - goes to the Krebs cycle.

2 carbon dioxide - is released as a waste product

2 reduced NAD - to oxidative phosphorylation.

Question 10

Describe the stages of the Krebs cycle.

Answer 10

Takes place in the mitochondrial matrix.

1) The acetyl group (2C) from acetyl CoA is combined with oxaloacetate (4C) to form citrate- citric acid (6C). This is catalysed by citrate synthase and coenzyme a goes back to the kink reaction to be used again.

2) The 6C citrate molecule is converted into a 5C molecule as decarboxylation occurs, where carbon dioxide is removed. Dehydrogenation also occurs, where the hydrogen is used to produce reduced NAD from NAD.

3) This 5C molecule is converted back into oxaloacetate 4C. Decarboxylation occurs as well as dehydrogenation and this produces carbon dioxide, one molecule of reduced FAD and two molecules of reduced NAD. ATP is produced by the direct transfer of a phosphate group from an intermediate compound to ADP and this is called substrate-level phosphorylation.

Question 11

What are the products of the Krebs cycle?

Answer 11

1 coenzyme A - goes back to the links reaction to be reused.

Oxaloacetate - regenerated for use in the Krebs cycle

2 CO2- released as a waste product.

1 ATP - used for energy

3 reduced NAD- to oxidative phosphorylation

1 reduced FAD - to oxidative phosphorylation.

Question 12

What is oxidative phosphorylation?

Answer 12

It is the process where the energy carried by electrons, from reduced coenzymes, is used to make ATP.

Question 13

Describe the process of oxidative phosphorylation.

Answer 13

This takes place in the inner mitochondrial membrane.

1) NADH and FADH are oxidised and the hydrogen atoms are released into the mitochondrial matrix where they split into protons and electrons.

2) The electrons that are formed due to the splitting of hydrogen atoms are passed onto electron carriers which are embedded within the inner mitochondrial membrane and travel along a series of electron carriers known as the electron transport chain.

3) As the electrons travel between the electron carriers, they lose energy. The energy that is lost is used to pump hydrogen ions/protons from the mitochondrial matrix across the inner membrane

4) The concentration of protons is now higher in the intermembrane space than in the mitochondrial matrix- this forms an electrochemical gradient.

5) Protons move down the electrochemical gradient, back into the mitochondrial matrix, via ATP synthase.

6) This movement drives the synthesis of ATP from ATP and an inorganic phosphate. This process of ATP production driven by the movement of H+ ions across a membrane (due to electrons moving down an electron transport chain) is called CHEMIOSMOSIS.

7) In the mitochondrial matrix, at the end of the transport chain, the protons, electrons and oxygen (from the blood) combine to form water. Oxygen is said to be the final electron acceptor.

1/2O2 +2H+ —-> H2O

Question 14

What is Anaerobic respiration?

Answer 14

It is a type of respiration that doesn’t require oxygen.

It starts of with glycolysis also.

Question 15

What are the two types of anaerobic respiration?

Answer 15

• Alcoholic fermentation.
• Lactate fermentation.

Question 16

What is lactate fermentation?

Answer 16

Takes place in the cytoplasm.
Occurs in mammals and produces lactate.

Firstly glycolysis occurs and reduced NAD from glycolysis transfers hydrogen to pyruvate to form NAD and lactate- lactic acid.

NAD can then be reused in glycolysis.

Our cells can tolerate a high level of lactate for short periods of time- for example, during short periods of hard exercise, when cells can’t get enough ATP from aerobic respiration.

Too much lactate is toxic and is removed from cells into the bloodstream where it is taken by the liver and converts it back into glucose in a process called gluconeogenesis.

Question 17

What is alcoholic fermentation?

Answer 17

also takes place in the cytoplasm of yeast cells and glycolysis must first occur.

1) Carbon dioxide is removed from pyruvate to form ethanal- decarboxylation.

2) Reduced NAD (from glycolysis) transfers hydrogen to ethanal to form ethanol and NAD.

NAD can then be reused in glycolysis- the production of ethanol also regenerates NAD so glycolysis can continue when there isn’t much oxygen around.

Question 18

Why does anaerobic respiration produce a much lower ATP yield than aerobic respiration?

Answer 18

This is because anaerobic respiration only has one energy- releasing stage which is glycolysis, which only produces 2 ATP per glucose molecule.

The energy-releasing reactions of the Krebs cycle and oxidative phosphorylation need oxygen, so they cannot occur during anaerobic respiration.

Question 19

What is a respiratory substrate?

Answer 19

It is any biological molecule that can be broken down in respiration to release energy.

Different respiratory substrates release different amounts of energy in respiration:

Lipids release the most, followed by proteins and carbohydrates release the least.

Question 20

Why do the respiratory substrate lipids have the highest energy value?

Answer 20

This is because most ATP is made in oxidative phosphorylation, which requires hydrogen atoms from NADH and FADH.

This means that respiratory substrates that contain more hydrogen atoms per unit mass cause more ATP to be produced when respired.

Lipids contain the most hydrogen atoms per unit of mass, followed by proteins and then carbohydrates.

Question 21

What is the respiratory quotient?

Answer 21

It is the volume/molecule of CO2 produced when that substrate is respired, divided by the volume/molecule of oxygen consumed in a set period of time.

RQ= Volume of CO2 released / volume of O2 consumed

Question 22

What is the RQ for lipids, proteins and carbohydrates?

Answer 22

Lipids = 0.7

Proteins = 0.9

carbohydrates = 1

Question 23

What does RQ tell you?

Answer 23

Under normal conditions, the usual RQ for humans is between 0.7 and 1- and RQ in this range shows that lipids are being used for respiration as well as carbohydrates such as glucose. Protein isn’t normally used by the body for respiration unless there’s nothing.

High RQs - greater than 1- means that an organism is short of oxygen and is having to respire anaerobically as well as aerobically.

Plants sometimes have a low IQ as the CO2 released in respiration is used for photosynthesis and therefore isn’t measured

Question 24

Describe the practical investigating the respiration rates of yeast - under aerobic respiration conditions.

Answer 24

1) put a known volume and concentration of substrate solution -e.g. glucose- in a test tube.

2) Add a known volume of buffer solution to keep the pH constant - usually 4-6.

3)Place the test tube into a water bath set to 25 degrees and this ensures that the temperature stays constant throughout the experiment. Leave for 10 mins to allow the temperature of the substrate to stabilise.

4) Add a known mass of dried yeast to the test tube and stir for 2 mins.

5) After the yeast has dissolved into the solution, put a bung with a tube attached to a gas syringe in the top of the test tube. The gas syringe should be set to zero.

6) Start a stop watch as soon as the bung has been put in the test tube.

7) 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 released.

8) At regular time intervals, record the volume of CO2 that is present in the gas syringe and do this for a set amount of time.

9) A control experiment should also be set up where no yeast is present and no CO2 should be formed without the yeast.

10) Repeat the experiment 3 times and use your data to calculate the mean rate production of CO2

Question 25

Describe the practical investigating the respiration rates of yeast - under anaerobic respiration conditions.

Answer 25

Set up apparatus similar to under aerobic conditions.

2) After the yeast has dissolved into the substrate solution, trickle some liquid paraffin down the inside of the test tube so that it settles on an completely covers the surface of the solution.
This will stop oxygen getting in, which will force the yeast to respire anaerobically.

3) Put a bung, with a tube attached to a gas syringe, in the top of the test tube. The gas syringe should be set to zero

4) Perform steps 6-10 from the method of under aerobic respiration conditions.

Question 26

Describe the practical ‘using a respirometer to measure oxygen consumption’.

Answer 26

The rate of respiration is measured using a piece of apparatus called a respirometer and works by measuring either the amount of oxygen used up by an organism or the amount of carbon dioxide produced. The faster the amount of oxygen consumed, the faster the rate of respiration.

You would set up the respirometer, with respiring organisms (such as woodlice) in one test tube connected to another test tube by a manometer.

The manometer contains a coloured liquid which will move closer towards the respiring test tube as oxygen is consumed.

The test tube on the right is a control test tube, containing a non-respiring substance, such as glass beads. The purpose of the control tube is to ensure that only respiration is causing the movement of liquid in the manometer.

The control tube should be as similar as possible to the test tube e.g., the glass beads should be the same mass as the woodlice.

In each test tube you need to add the same volume of potassium hydroxide solution which absorbs carbon dioxide - this ensures that the movement of the liquid is only affected by the decreasing levels of oxygen.

Once the apparatus has been set up, it is left for a certain period of time (e.g., 30 minutes). This will allow for the potassium hydroxide to absorb all the carbon dioxide in the test tubes. You then record the distance moved by the liquid in the manometer in a given time, using the calibrated scale and a stopwatch. You then calculate the volume of oxygen taken in by the woodlice per minute. Repeat the experiment at least three times and calculate a mean.