Respiration

• Aerobic respiration uses oxygen to help release energy
• When not enough oxygen is available, some cells, for example muscles and organisms like yeast, can still release a small amount of the energy in food molecules using a series of reactions known as anaerobic respiration
• Anaerobic respiration in human muscles causes lactic acid to build up, leading to muscle soreness
• Anaerobic respiration by yeast produces alcohol (ethanol) and is the basis of wine, beer and bread production
• Demonstrating anaerobic respiration in yeast

  1. Boil glucose solution to remove dissolved oxygen

  2. Add yeast cells

  3. Place in apparatus to collect carbon dioxide and heat produced
• Anaerobic respiration demonstration with yeast

  • Figure 5.1
• Factors affecting respiration of yeast

  • Temperature
  • Type of sugar
• Investigating effect of temperature on respiration of yeast

  1. Mix yeast, glucose and water

  2. Leave at room temp for 1 hour

  3. Fill small test tube with mixture

  4. Invert over larger tube

  5. Place in water bath at different temperatures

  6. Measure height of bubble after 30 minutes
• DAS students are expected to carry out practical work to investigate the respiration of yeast, but do not do so as a prescribed practical
• Investigating effect of different sugars on respiration of yeast

  1. Mix yeast, glucose and water

  2. Leave at room temp for 1 hour

  3. Fill small test tube with mixture

  4. Invert over larger tube

  5. Place in 20°C water bath

  6. Repeat with sucrose, fructose, lactose and maltose

  7. Measure height of bubble after 30 minutes
• Sugars tested for effect on yeast respiration

  • Glucose
  • Sucrose
  • Fructose
  • Lactose
  • Maltose
• The respiratory system is inside the thorax, a space surrounded by ribs of bone with intercostal muscles between them and a muscular sheet, the diaphragm below
• Respiratory surfaces (alveoli)

  • Large surface area
  • Thin walls with short diffusion distances
• In humans, gas exchange takes place in the alveoli, where oxygen diffuses into the blood and carbon dioxide diffuses from the blood
• Respiratory surfaces

  • Large surface area
  • Thin walls with short diffusion distances
  • Moist walls
  • Permeable surfaces
  • Good blood supply
• In humans, gas exchange takes place in the alveoli
• Oxygen diffuses into the blood and carbon dioxide diffuses from the blood into the alveoli, where it is then breathed out
• Respiratory surfaces in plants

  • The main respiratory surfaces are the spongy mesophyll cells surrounding the air spaces in the leaves
  • There are a lot of cells in contact with the air spaces, giving a large surface area
  • The cell membranes where gas exchange takes place are thin
• The process of breathing

  1. Diaphragm moves down

  2. Volume inside glass jar increases

  3. Pressure inside glass jar decreases

  4. Air enters the lungs until pressures equalise
• The process of breathing in humans is more complicated than the lung model
• Differences between lung model and human breathing

  • In humans, the ribs move out and in and work with the diaphragm
  • In humans, the diaphragm is normally domed shaped and flattens when breathing in
  • The space between the lungs and chest wall is much greater in the model than in reality
  • Pleural membranes line the inside of the chest wall and outside of the lungs to reduce friction
• The pleural membranes contain pleural fluid to further reduce friction during breathing
• Levels of fitness

  • Breathing rate
  • Recovery time
• Exercise increases the depth of breathing as well as the rate