2.8 Cell Respiration

Energy in cells is all about the molecule shown, Adenosine Triphosphate (ATP). The energy is held in the bonds between atoms, in particular the high energy bond that joins the second and third phosphates. ATP is the energy currency of the cell. Hence the efficiency of respiration is measured by the yield of ATP.

http://commons.wikimedia.org/wiki/File:ATP_chemical_structure.png

2.8 Cell respiration

• Essential idea: Cell respiration supplies energy for the functions of life.

Introduction:• All forms of life depend directly or

indirectly on light energy captured during photosynthesis

• Photosynthesis is done by plants to make glucose

• In cellular respiration, glucose molecules are broken down back into carbon dioxide and water (molecules the plant started with)

• Cell respiration is the controlled release of energy from organic compounds in cells to form ATP.

2.8.U1 Cell respiration is the controlled release of energy from organic compounds to produce ATP.

Cell respirationThe controlled release of energy from organic compounds in cells to form ATP

2.8.U1 Cell respiration is the controlled release of energy from organic compounds to produce ATP.

2.8.U1 Cell respiration is the controlled release of energy from organic compounds to produce ATP.

2.8.U1 Cell respiration is the controlled release of energy from organic compounds to produce ATP.

2.8.U1 Cell respiration is the controlled release of energy from organic compounds to produce ATP.

2.8.U2 ATP from cell respiration is immediately available as a source of energy in the cell.

2.8.U2 ATP from cell respiration is immediately available as a source of energy in the cell.

2.8.U2 ATP from cell respiration is immediately available as a source of energy in the cell.

• All processes release heat energy and hence all

energy eventually ends up as heat.

• The heat energy initially can be used to raise the

temperature of the organism, …

• … but eventually it is lost to the environment and

cannot be used for metabolic processes.

2.8.U1 Cell respiration is the controlled release of energy from organic compounds to produce ATP.

This links to 2.5 Enzymes and 8.1 Metabolism (AHL)

2.8.U4 Aerobic cell respiration requires oxygen and gives a large yield of ATP from glucose.

2.8.U4 Aerobic cell respiration requires oxygen and gives a large yield of ATP from glucose.

Main steps of cell respiration:

1. Glycolysis

2. Link Reaction

3. Krebs Cycle

4. Electron Transport Chain

Occurs if oxygen is present

(aerobic)

Does not require oxygen

(anaerobic)

2.8.U4 Aerobic cell respiration requires oxygen and gives a large yield of ATP from glucose.

Step 1: Glycolysis• Does not require oxygen (anaerobic)• Occurs in the cytoplasm• 2 ATP are used to split glucose into two 3 C molecules of G3P (aka

PGAL) • Each G3P molecule goes through a series of reactions that convert it

into pyruvate (aka pyruvic acid) • During these reactions, 2 high energy electrons and a H+ are added to

NAD+ to form an energy carrier NADH – 2 NADH are made • 2 ATPs are made per G3P for a total of 4 – however, net gain is only

2 ATPs

2.8.U4 Aerobic cell respiration requires oxygen and gives a large yield of ATP from glucose.

Step 2: Link Reaction• Occurs in matrix of mitochondria• Two molecules of pyruvate produced by glycolysis are

transported across both mitochondrial membranes into matrix

• Each pyruvate is split into CO2 and a 2 C acetyl group which immediately attaches to coenzyme A to form acetyl CoA – during this reaction NADH is produced (oxidative piece)

2.8.U4 Aerobic cell respiration requires oxygen and gives a large yield of ATP from glucose.

Step 3: Krebs Cycle • Acetyl CoA’s (2 C) enter Krebs cycle by briefly combining with

oxaloacetate (4 C) to form citrate (6 C) – coenzyme A is released to be reused

• Kreb’s cycle rearranges citrate to regenerate oxaloacetate (4 C) giving off 2 CO2, 1 ATP and four electron carriers (1 FADH2 and 3 NADH) per pyruvate molecule (x2 per glucose molecule)

citrate (6 C)

Oxaloacetate(4 C)

Cytoplasm Matrix of Mitochondria

2.8.U4 Aerobic cell respiration requires oxygen and gives a large yield of ATP from glucose.

Step 4: Electron Transport Chain• Located in inner mitochondrial membrane• Energetic electrons from NADH and FADH2 move

from molecule to molecule along transport system• Energy released by electrons is used to pump H+

ions from the matrix into the intermembrane compartment

• At the end of the ETC, oxygen and H+ ions accept the electrons to form H2O

• H+ ions pumped across the inner membrane generate a large H+ concentration gradient (high concentration in intermembrane compartment and low concentration in matrix)

• Inner membrane is impermeable to H+ ions • H+ ions must flow through ATP synthase• The flow of H+ ions provides energy to synthesize 32

– 34 ATPs from ADP

2.8.S1 Analysis of results from experiments involving measurement of respiration rates in germinating seeds or invertebrates using a respirometer.

http://www.nuffieldfoundation.org/sites/default/files/PB_measuring-rate-of-metabolism-respirometer2-500.

jpg

The diagram shows the design of a typical respirometer. They vary greatly in their design, but all can be used to calculate the rate of respiration by measuring the consumption of oxygen.

2.8.S1 Analysis of results from experiments involving measurement of respiration rates in germinating seeds or invertebrates using a respirometer.

http://www.nuffieldfoundation.org/sites/default/files/PB_measuring-rate-of-metabolism-respirometer2-500. jpg

The diagram shows the design of a typical respirometer. They vary greatly in their design, but all can be used to calculate the rate of respiration by measuring the consumption of oxygen.

Potassium hydroxide (alkali) solutionHydroxide solutions are used to absorb carbon dioxide in the air

Filter paper wicksIncrease the efficiency of carbon dioxide absorption

Aerobic respiration uses 6 molecules of gas (oxygen) and creates 6 molecules of gas (carbon dioxide) = no change in volume, but …

… carbon dioxide is absorbed therefore the volume of gas in the respirometer decreases.

Respiring organismSuitable living organism will respire aerobically

2.8.S1 Analysis of results from experiments involving measurement of respiration rates in germinating seeds or invertebrates using a respirometer.

http://www.nuffieldfoundation.org/sites/default/files/PB_measuring-rate-of-metabolism-respirometer2-500. jpg

The diagram shows the design of a typical respirometer. They vary greatly in their design, but all can be used to calculate the rate of respiration by measuring the consumption of oxygen.

Capillary tube containing coloured oilMovement in the oil per minute toward tube B measures the rate of oxygen consumption. If the diameter of the capillary tube is known then a volume can be calculated

Rubber bungs seal tubesCloses the system to prevent changes in air volume not due to respiration

SyringeUsed to reset the position of the coloured oil

Metal cageKeeps the organism in place and away from contact with the hydroxide solution.

2.8.S1 Analysis of results from experiments involving measurement of respiration rates in germinating seeds or invertebrates using a respirometer.

http://www.nuffieldfoundation.org/sites/default/files/PB_measuring-rate-of-metabolism-respirometer2-500. jpg

The diagram shows the design of a typical respirometer. They vary greatly in their design, but all can be used to calculate the rate of respiration by measuring the consumption of oxygen.

Temperature controlledThe respirometer is immersed in a water bath to prevent temperature affecting the pressure and hence volume of air in the apparatus.

Hoffman clipSeals the respirometer and can be opened to reset it after the volume has been reduced by oxygen consumption.

n.b. due to gas expansion the Hoffman clip should be left open until the respirometer is at the desired temperature – if not an explosion can result.

2.8.S1 Analysis of results from experiments involving measurement of respiration rates in germinating seeds or invertebrates using a respirometer.

http://www.nuffieldfoundation.org/sites/default/files/PB_measuring-rate-of-metabolism-respirometer2-500. jpg

The diagram shows the design of a typical respirometer. They vary greatly in their design, but all can be used to calculate the rate of respiration by measuring the consumption of oxygen.

Tube AActs as a control to ensure that changes in the level of coloured oil are due to respiration, not the reaction of the akali with atmospheric gases other than carbon dioxide.

Nature of Science: assessing the ethics of scientific research - the use of invertebrates in respirometer experiments has ethical implications. (4.5)

http://www.nuffieldfoundation.org/sites/default/files/PB_measuring-rate-of-metabolism-respirometer2-500. jpg

The diagram shows the design of a typical respirometer. They vary greatly in their design, but all can be used to calculate the rate of respiration by measuring the consumption of oxygen.

Respiring organism: If using invertebrates rather than seeds what are the ethical questions that need answering?

Nature of Science: assessing the ethics of scientific research - the use of invertebrates in respirometer experiments has ethical implications. (4.5)

http://www.nuffieldfoundation.org/sites/default/files/PB_measuring-rate-of-metabolism-respirometer2-500. jpg

The diagram shows the design of a typical respirometer. They vary greatly in their design, but all can be used to calculate the rate of respiration by measuring the consumption of oxygen.

Respiring organism: If using invertebrates rather than seeds what are the ethical questions that need answering?

• Is it acceptable to remove animals from their natural habitat for use in an experiment?• Can the animals be safely returned to their habitat?• Will the animals suffer pain or any other harm during the experiment?• Can the risk of accidents that cause pain or suffering to the animals be minimized during

the experiment? In particular, can contact with the alkali be prevented?• Is the use of animals in the experiment essential or is there an alternative method that

avoids using animals?

2.8.U3 Anaerobic cell respiration gives a small yield of ATP from glucose.

Anaerobic cell respiration

Step 1: Glycolysis

2.8.U3 Anaerobic cell respiration gives a small yield of ATP from glucose.

1. Alcoholic fermentation• Occurs in plants, many

yeasts & some bacteria

2. Lactic acid fermentation• Occurs in animal

muscle cells

Step 2: FermentationThere are two types of fermentation:

In anaerobic conditions:

Without fermentation, NADH would not be able to be converted back to NAD+ and no more pyruvate would be made.

In other words, without fermentation, glycolysis could not continue and ATP production would stop.

2.8.U3 Anaerobic cell respiration gives a small yield of ATP from glucose.

2.8.A1 Use of anaerobic cell respiration in yeasts to produce ethanol and carbon dioxide in baking.

Ethanol is also produced by anaerobic cell respiration, but it evaporates during baking.

http://commons.wikimedia.org/wiki/File:Frenchbread3000ppx.jpg

Bread is made by adding water to flour, kneading the mixture to make dough and then baking it. Usually an ingredient is added to the dough to create bubbles of gas, so that the baked bread has a lighter texture (e.g. yeast).

After kneading (mixing) the dough is kept warm to encourage the yeast to respire.

Yeast can respire aerobically or anaerobically, but oxygen in the dough is soon used up so the yeast is forced to respire anaerobically.

The carbon dioxide produced by anaerobic cell respiration cannot escape from the dough and forms bubbles causing the dough to swell and rise.

http://en.wikipedia.org/wiki/File:Ethanol_plant.jpg

http://en.wikipedia.org/wiki/File:Saab_9-3_SportCombi_1.8t_BioPower_Facelift_rear.JPG http://commons.wikimedia.org/wiki/File:Cornfield_in_South_Africa2.jpg

Bioethanol (ethanol produced by organisms) is a renewable energy source.

2.8.A1 Use of anaerobic cell respiration in yeasts to produce ethanol and carbon dioxide in baking.

Most bioethanol is produced from sugar cane and maize, using yeast.

Fermenters are used to keep the yeast in optimum conditions.

When yeast carry out anaerobic respiration the sugars in the plant material are converted to ethanol and carbon dioxide.

Starch and cellulose in the plant material are broken down by enzymes into sugars.

The ethanol produced by the yeasts is purified by distillation and water is removed to improve combustion.

2.8.A2 Lactate production in humans when anaerobic respiration is used to maximize the power of muscle contractions.

Certain human activities require anaerobic respiration such as weightlifting and sprinting.

Rapid generation of ATP enables us to maximise the power of muscle contractions.

Aerobic respiration generates a much greater yield of ATP, but anaerobic respiration can supply ATP very rapidly, as oxygen is not required.

Anaerobic cell respiration produces lactate. There is a limit to the concentration that the body can tolerate and this limits how much or how long anaerobic respiration can be done for.

Afterwards lactate must be broken down. This involves the use of oxygen. It can take several minutes for enough oxygen to be absorbed for all lactate to be broken down. The demand for oxygen that builds up during a period of anaerobic respiration is called the oxygen debt.

• Cellular Respiration video: https://youtu.be/JnQqbMg74Hk