Topic 7

• Aerobic respiration


  1. Glycolysis

  2. Link reaction

  3. Krebs cycle

  4. Oxidative phosphorylation
• During aerobic respiration, glucose is effectively burned inside our bodies (it reacts with oxygen) to produce carbon dioxide, water and lots of energy in the form of ATP
• The overall equation for aerobic respiration is
• Glycolysis


  1. Glucose is phosphorylated using ATP

  2. Glucose is converted into two 3-carbon pyruvate molecules

  3. Hydrogen is removed from triose phosphate and transferred to NAD to form NADH

  4. Net gain of 2 ATP
• Link reaction


  1. Pyruvate is converted into acetyl CoA

  2. Carbon dioxide and NADH are produced
• Krebs cycle


  1. Acetyl CoA reacts with oxaloacetate to form citrate

  2. Citrate is converted back to oxaloacetate

  3. ATP, NADH and FADH2 are produced
• Oxidative phosphorylation


  1. NADH and FADH2 release electrons which travel along the electron transport chain

  2. Electron transport chain pumps hydrogen ions across the inner mitochondrial membrane

  3. Hydrogen ions flow back through ATP synthase, driving the production of ATP
• Aerobic respiration produces a total of 38 ATP molecules per one molecule of glucose respired
• Respirometer


  Apparatus used to measure the rate of respiration by measuring oxygen consumed or carbon dioxide produced
• Setting up a respirometer

  1. Place respiring organisms in one test tube connected to a manometer

  2. Add potassium hydroxide to absorb carbon dioxide

  3. Include a control test tube with non-respiring substance

  4. Measure distance moved by liquid in manometer over time to calculate oxygen consumption rate
• Respiration can also occur in the absence of oxygen - this is called anaerobic respiration
• Anaerobic respiration


  1. Glycolysis produces 2 ATP and 2 NADH

  2. NADH donates hydrogen to pyruvate, producing lactate and regenerating NAD
• Continued anaerobic respiration results in the build-up of lactate, which needs to be broken down
• Cells can convert lactate back into pyruvate, which is then able to enter aerobic respiration at the Krebs cycle
• Liver cells have the ability to convert lactate into glucose, which can then be respired aerobically (if oxygen is now present) or stored for later use
• Oxygen enters the lungs during inspiration (inhalation) and carbon dioxide leaves the lungs during expiration (exhalation).
• Gas exchange occurs at the alveoli, which are tiny air sacs found within the lungs.
• The respiratory system is responsible for the exchange of gases between an organism's body and its environment.
• Alveoli are tiny air sacs where gas exchange occurs between the bloodstream and lungs.
• Gas exchange occurs through diffusion, which involves particles moving from areas of high concentration to low concentration until equilibrium is reached.
• The diaphragm contracts and moves downwards, increasing the volume of the thoracic cavity.
• The walls of the alveoli contain thin membranes that allow gases to diffuse easily between them and the blood vessels surrounding them.
• This decrease in pressure causes air to rush in through the nose/mouth, filling the lungs with fresh air.
• During exhalation, the diaphragm relaxes and returns to its original position, decreasing the volume of the thoracic cavity.
• During inspiration, diaphragm contracts and ribcage moves upwards, increasing lung volume and decreasing pressure inside the lungs.
• Inspiration involves the contraction of diaphragm muscles and intercostal muscles, resulting in increased volume of thoracic cavity and decreased pressure inside it compared to atmospheric pressure.
• Inspiration involves the contraction of diaphragm muscles and intercostal muscles, resulting in increased lung volume and decreased pressure inside the thorax compared to atmospheric pressure.
• Expiration involves relaxation of diaphragm and intercostal muscles, leading to decreased volume of thoracic cavity and increased pressure inside it compared to atmospheric pressure.
• Inspiration (breathing in): Diaphragm contracts downwards, increasing volume of thoracic cavity; intercostal muscles contract, raising ribcage upwards, further increasing volume of thoracic cavity; pressure inside thorax decreases relative to atmospheric pressure, causing air to rush in.
• Expiration involves relaxation of diaphragm and intercostal muscles, leading to decreased lung volume and increased pressure inside the thorax compared to atmospheric pressure.
• During exercise, breathing rate increases due to increased demand for oxygen by working muscles.
• During exercise, breathing rate increases due to increased demand for oxygen by working muscles.
• During exercise, breathing rate increases due to increased demand for oxygen by working muscles.
• Inspiration is also known as inhalation or breathing in.
• Oxygen enters the bloodstream via simple diffusion across the walls of the alveoli into the capillaries.
• Expiration (breathing out): Diaphragm relaxes back to resting position, reducing volume of thoracic cavity; intercostal muscles relax, lowering ribcage, further reducing volume of thoracic cavity; pressure inside thorax increases relative to atmospheric pressure, causing air to leave.
• As the volume of the thoracic cavity decreases, the pressure inside it increases, causing air to be pushed out of the lungs.
• Carbon dioxide leaves the bloodstream by simple diffusion across the walls of the capillaries into the alveoli.
• During inspiration, the intercostal muscles contract and move upwards, expanding the ribcage and increasing the volume of the thorax.
• Oxygen (O2) molecules move into the bloodstream via simple diffusion across the thin membrane separating the alveolus from the capillaries.