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To review the process of respiration (aerobic and anaerobic). …

To review the process of respiration (aerobic and anaerobic).
Course = Edexcel A2 Biology - Topic 7.1.

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  • Boardworks A2 Biology Respiration
  • Boardworks A2 Biology Respiration
  • Teacher notes See the Boardworks AS Biology ‘ Cell Structure ’ presentation for more information about the mitochondria. Photo credit: © CNRI / Science Photo Library Mitochondrion, coloured transmission electron micrograph (TEM). Mitochondria are a type of organelle found in the cytoplasm of eukaryotic cells. They oxidise sugars and fats to produce energy in a process called respiration. A mitochondrion has two membranes, a smooth outer membrane and a folded inner membrane. The folds of the inner membrane are called cristae, and it is here that the chemical reactions to produce energy take place. Magnification: x62,800 when printed at 10 centimetres wide. Boardworks A2 Biology Respiration
  • Teacher notes This activity requires students to combine their knowledge of mitochondrial structure with the biochemical pathways of respiration, and is therefore quite advanced. It should provoke discussion, and students could be asked to list other adaptations of mitochondria to their role as the respiratory organelle. An explanation of the answers is provided below. Outer membrane – This controls everything that enters and leaves the mitochondrion. As such it requires specialized proteins to actively import pyruvate for the link reaction and oxygen for the ETC. It also needs to transport CO 2 to the cell cytoplasm so that it can be removed from the cell, and supply the cell with the ATP produced in respiration. Inner membrane – The inner membrane is the site of the ETC. It needs to be impermeable to H + ions in order to maintain the chemical gradient required for chemiosmosis, and is rich in ATP synthase to maximize ATP production. Students may also comment on its large surface area increasing reaction rate, and its high protein content. Matrix – The matrix is the site of both the link reaction and Krebs cycle. Both of these processes require enzyme action. The matrix contains its own DNA loop, which encodes these enzymes, along with a large number of ribosomes to synthesize them. Intermembrane space – This space is relatively small, this acts to increase the concentration of H + ions as they are pumped into it by the ETC. This high concentration increases the rate of ATP regeneration. Boardworks A2 Biology Respiration
  • Boardworks A2 Biology Respiration 7
  • Boardworks A2 Biology Respiration
  • Don’t worry about the last bullet point we will go over this when we look at the Krebs Cycle in more detail.
  • Teacher notes Anaerobic respiration in mammals occurs primarily in the muscle tissue. Here it is used to allow continued movement despite a limited oxygen supply. The production of lactate is a reversible reaction. This means that lactate can be transported away from muscle tissue to limit fatigue and later be converted back to pyruvate, where it can enter the aerobic respiratory pathway, producing the maximum amount of ATP. Boardworks A2 Biology Respiration
  • Boardworks A2 Biology Respiration
  • Boardworks A2 Biology Respiration
  • Boardworks A2 Biology Respiration
  • Teacher notes It should be highlighted that when NADH is oxidized, NADH dehydrogenase is reduced because the reaction is a redox reaction. The carrier proteins are oxidized and reduced as the electrons pass along the transport chain. Students may need to be reminded that oxidation is loss of electrons and reduction is gain of electrons. As the final electron and hydrogen acceptor, oxygen is crucial to the process. Without oxygen the redox reaction cannot be repeated, leaving the ETC saturated. This leaves glycolysis as the only source of ATP. Cyanide is a well known poison that works by blocking the ETC. It is a non-competitive inhibitor to cytochrome oxidase. This means that it can block the donation of electrons and hydrogen to oxygen, halting aerobic respiration entirely. See the Boardworks AS Biology ‘ Enzymes ’ presentation for more information about competitive inhibition. Boardworks A2 Biology Respiration
  • Boardworks A2 Biology Respiration
  • Teacher notes Each molecule of glucose forms two molecules of pyruvate, so the link reaction and Krebs cycle happen twice per glucose molecule. The figures for the number of ATPs yielded by chemiosmosis for NADH and FADH 2 are still debated among biochemists. However, students should be able to see that FADH 2 yields less ATP than NADH because it enters the electron transport chain later so leads to fewer hydrogen ions moving into the intermembrane space. In addition, it is important to note that the figure of 32 ATP is only a theoretical yield, and it is rarely obtained. For more information, see slide 29 of this presentation. Students could use the diagram in the activity on slide 19 of this presentation to trace where the ATP, NADH and FADH 2 are produced in the process. Boardworks A2 Biology Respiration
  • Teacher notes Anaerobic respiration in mammals occurs primarily in the muscle tissue. Here it is used to allow continued movement despite a limited oxygen supply. The production of lactate is a reversible reaction. This means that lactate can be transported away from muscle tissue to limit fatigue and later be converted back to pyruvate, where it can enter the aerobic respiratory pathway, producing the maximum amount of ATP. Boardworks A2 Biology Respiration
  • Boardworks A2 Biology Respiration
  • Boardworks A2 Biology Respiration


  • 1. Energy & Respiration Topic 7.1
  • 2. The Need for Energy…Living Organisms need a constant supply of energy to drive the metabolic reactions that take place inside their cells.This includes:• Movement (muscular contractions)• Maintaining constant Body Temperature• Making new compounds (biosynthesis - as forming new chemical bonds requires energy)• Getting things in and out of cells (active transport)
  • 3. Summary of Energy Uses: All organisms get their energy from Respiration, this involves the Molecular breakdown of glucose (whichMechanical transport comes from our food) and it usually(Muscles) (Across involved oxygen from the air. Membranes) Can you remember the equation for Respiration? The chemical bond energy in your food could be release by burning (combustion) but this reaction isBiosynthesis Heat (Temp uncontrolled and would be fatal (making control) inside our cells!molecules in the cell) Respiration involves the gradual release of energy in controlled small steps which release small amounts of energy to make a molecule called ATP…
  • 4. Types of respiration During aerobic respiration, a respiratory substrate, e.g.glucose, is split in the presence of oxygen to release carbon dioxide and water. A large number of ATP molecules are produced, releasing the energy from the glucose. C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + 36 ATP In anaerobic respiration, glucose is converted (in the absence of oxygen) to either lactate or ethanol. A small number of ATP molecules are produced. C6H12O6 → 2 C2H5OH + 2 CO2 + 2 ATP ethanol C6H12O6 → 2 C3H6O3 + 2 ATP lactate
  • 5. Where does respiration occur? Respiration occurs in all living cells. In eukaryotes the earlystages of respiration occur in the cytoplasm. The later stages of respiration are restricted to the mitochondria. Mitochondria contain highly folded inner membranes that hold key respiratory proteins (including the enzyme that makes ATP) over a large surface area. Mitochondria provide an isolated environment to maintain optimum conditions for respiration. Mitochondria have their own DNA and ribosomes, so can manufacture their own respiratory enzymes.
  • 6. The structure of the mitochondria
  • 7. Adaptations of mitochondria
  • 8. An overview of respiration
  • 9. Stages in Aerobic RespirationThere are four main stages in the breakdown of glucose duringaerobic respiration:• glycolysis (in the cytosol – cytoplasm of cell)• the link reaction (in mitochondrial matrix)• Krebs Cycle (in matrix)• electron transport chain (on cristae, inner membrane of mitochondria)You need to know about all 4 of these stages but not in as much detail asyour text suggests!
  • 10. Glycolysis – the 1st stageThis is the splitting (–lysis) of glucose. It takes place in a number of enzyme-controlled reactions and oxygen is not required. The process yields little energy but takes little time.1. Glucose molecule is phosphorylated to make hexose phosphate* (6C) [caused by the addition of a 2 phosphates from 2 ATP molecules]2. The 6-carbon hexose phosphate is split into two molecules of triose phosphate** (3C sugars)3. Each 3-carbon sugar is converted into pyruvate [takes places in a series or reactions where Hydrogen is removed reducing a molecule of NAD+ -> NADH and producing 2 ATP molecules!]Overall Glycolysis produces 4 molecules of ATP (but 2 are used), 2 molecules of pyruvate and 2 molecules of NADH…see flowchart on handout *sometimes referred to as fructose-6-phosphate **sometimes referred to as glyceraldehyde 3-phosphate
  • 11. The first stage of respiration: glycolysis
  • 12. The Link Reaction – 2nd stage If oxygen is present this next stage of aerobic respiration can take place:• Occurs in the matrix of mitochondria (Pyruvate from the end of theglycolysis stage enters through the double membrane from the cytoplasm)• Pyruvate (3C) combines with coenzyme A to form acetylcoenzyme A [Acetyl-CoA] (2C molecule)• In the process a molecule of CO2 and Hydrogen (2H) are removed• Acetyl-CoA then enters the next stage of Respiration…The Krebs Cycle … where it combines with a 4C compoundOxaloacetate to form Citrate (6C) Coenzyme A 2H Pyruvate Acetyl-CoA [3C] CO2 [1C] [2C]
  • 13. The fate of pyruvate
  • 14. The Krebs CycleThis series of reaction was discovered by Sir Hans Kreb in 1937, it is also known as the Citric Acid Cycle.• The Krebs cycle occurs in matrix of mitochondria• Remember: Acetyl coenzyme A (2C) combines with Oxaloacetate (4C) to form Citrate (6C)• A series of other reactions take place in which Citrate (6C) is both decarboxylated [CO2 removed] and dehydrogenated [Hydrogens removed]• Carbon dioxide is removed as a waste product & Hydrogen atoms are picked up by H acceptors (like NAD).The most important part of the Krebs Cycle is the release of hydrogenions to be used in the Electron Transport System for generation of ATP
  • 15. Krebs cycle
  • 16. Counting carbons
  • 17. Keeping track of the products For each molecule of glucose, glycolysis produces:  2×  2×  2×For each molecule of glucose, the link reaction produces:  2×  2 ×  2 ×
  • 18. Keeping track of the products For each molecule of glucose, Krebs cycle generates:  4× produced by decarboxylation  6× produced by redox reactions  2× produced by redox reactions  2× produced by substrate-level phosphorylationThe NADH and FADH2 contain the potential energy originally locked in glucose. This energy is now transferred to ATP byoxidative phosphorylation in the electron transport chain.
  • 19. The Electron Transport Chain – 4th & final stageThe ETC allows the energy from Hydrogen atoms (removed from compounds in the previous stages) to be used to make large amounts of ATP. Oxygen is required and the reactions take place on the inner membrane (cristae) of the mitochondria.• NADH & FADH2 deliver H+ (protons) and e-(electrons) to cristae.• e-’s "transported" along cristae through electron acceptors, providingenergy to pump H+ from matrix into the intermembrane space.• Concentration of H+ is now higher in intermembrane space. H+ passthrough ATP synthases in the cristae back out to matrix.• Last step involves H+ & e- added to oxygen. This frees NAD+ toreturn to glycolysis & Krebs Cycle to pick up more H+ & e-.• The overall process of forming ATP in this way is called oxidativephosphorylation. 28 ATP are made in total.•The movement of H+ ions across a membrane to generate ATP iscalled chemiosmosis.
  • 20. The electron transport chain
  • 21. Outline of the Electron TC ATP ATP[Reduced Carrier 1] [Oxidised Carrier 2] ATP [Reduced Carrier 3] [Oxidised Carrier 4] NADH + H+ FAD Water 2H 2e- 2e- 2e- Oxygen[Oxidised Carrier 1] [Reduced Carrier 2] [Oxidised Carrier 3] NAD + FADH2 [Reduced Carrier 4] 2H+ Electrons being transported have come from these two H atoms
  • 22. Understanding the ETC
  • 23. How much ATP is produced? Process ATP in ATP produced Net ATP out glycolysis 2 4 2link reaction 0 0 0Krebs cycle 0 2 (per glucose) 2 (per glucose) Via the electron transport chain and chemiosmosis, each NADH can yield 2.5 ATP and each FADH2 1.5 ATP.From one molecule of glucose, glycolysis yields 2 NADH, the link reaction yields 2 NADH and the Krebs cycle yields 6 NADH and 2 FADH2.10 × 2.5 = 25 ATP from NADH 2 × 1.5 = 3 ATP from FADH2 total = 2 + 2 + 25 + 3 = 32 ATP overall
  • 24. Anaerobic RespirationAnaerobic respiration takes place in the absence of oxygen, and occurs via Glycolysis. Some organisms carry put aerobic respiration if O2 is available but are able to respire anaerobically in its absence.Most anaerobes fall into this category, some bacteria however can thrive in the absence of O2 – such as C. welccii which causes gangrene!The two main types of Anaerobic Respiration are:• Alcoholic Fermentation – carried out by yeast and plants• Lactic Acid (Lactate) Fermentation – takes place in animals
  • 25. Lactic Acid Fermentation
  • 26. The fate of pyruvate
  • 27. Comparison of aerobic and anaerobic respiration Aerobic Anaerobic Respiration respiration in animals in plants and yeastOxygen required? yes no noGlycolysis occurs yes yes yesATP yield 32ATP 2ATP 2ATPGlucose completely yes no no broke down?End products Carbon Lactic acid Ethanol and dioxide and carbon dioxide water
  • 28. Respiratory rate The respiratory rate is the rate at which an organismconverts glucose to CO2 andwater. It can be calculated bymeasuring an organism’s rate of oxygen consumption. Studies on simple animals often use a respirometer. Respirometers measure the change in gas volume in aclosed system. Any change is due to the respiratory activityof the study organisms. Potassium hydroxide or soda lime is used to absorb the carbon dioxide produced, meaning any changes in volume are due to oxygen consumption.
  • 29. The respirometer
  • 30. Respirometer experiments