• Learning objectives
    • define aerobic respiration
    • state the word equation for aerobic respiration
    • list uses of energy in the body
    • list uses of energy in the body
    • state the word equations for anaerobic respiration in plants and animals
    • describe the production and effects of lactic acids on muscles during exercise


  • is the oxidation of food substances eg carbohydrates with the release of energy.
  • it occurs in living cells.


Uses of energy

  • maintenance of constant body temperature
  • active transport
  • making protein molecules
  • muscle contraction
  • cell division
  • transmitting nerve impulses


Types of Respiration

  1. Aerobic respiration
  2. Anaerobic respiration


Aerobic Respiration

  • breakdown of glucose to carbon dioxide and water to release large amounts of energy in the presence of oxygen;
  • C6H12O6 + 6O2 → 6CO2 + 6H2O


Anaerobic Respiration

  • oxygen is not required.
  • small amounts of energy is released.
  • lactic acid produced in mammals;
  • ethanol and carbon dioxide produced in yeast
Alcoholic Fermentation- in yeast cells
  • Glucose → ethanol + CO2 + energy
Lactate/acidic Fermentation- eg in muscle cells
  • Glucose → lactic acid


Differences between anaerobic and anaerobic respiration

Aerobic Anaerobic
occurs in mitochondrion in cytoplasm
large amounts of energy released small amounts of energy released
water + carbon dioxide lactic acid or CO2 + ethanol
require oxygen oxygen not required


The organs for gaseous exchange are the lungs found inside the ribcage. Gases exchanged are oxygen and carbon dioxide.





Air Passage

Nasal Passage

  • the anterior most part which opens through external nostrils to the outside
  • it has hairs lining the nasal cavity- filter the air and trap large particles
  • moisture ie keeps the hairs moist
  • blood capillaries warm the incoming air.



  • trachea splits into two bronchi-one goes to each lung.
  • It contains cartilage rings which keep it open and prevent it from collapsing
  • is lined with a mucus layer and cilia
  • mucus trap pathogens like bacteria and dust particles
  • cilia move in a sweeping motion to keep the air passage clean
  • The bronchi split further into bronchioles
  • the bronchioles finally end at alveoli, where gas exchange take place


The process of diffusion

  • there will be more oxygen inside the alveoli than there is in the surrounding blood capillaries.
  • oxygen diffuses from the air sacs into the blood capillaries
  • it will be absorbed by red blood cells
  • There will be more carbon dioxide inside the blood capillaries than there is in air sacs
  • carbon dioxide will diffuse from the blood into the air sacs


Differences between inhaled and exhaled air

Inhaled air % Exhaled air %
Oxygen 20 16
Carbon dioxide 0,04 4
Nitrogen 79 79
Water vapor varies saturated
  • Oxygen is used during respiration.
  • Carbon dioxide is the product of respiration.
  • Nitrogen is not used directly by the body
  • water vapor is saturated because it is a product of respiration


  • lime water changes from clear to milky in the presence of carbon dioxide.
  • Bicarbonate indicator changes from red to yellow in the presence of carbon dioxide.


Breathing Mechanism


  • external intercostal muscle contract
  • internal intercostal muscle relax
  • ribs moves upwards and outwards
  • diaphragm contracts and flattens
  • volume of thorax decreases
  • air flows into lungs



  • external intercostal muscle relax
  • internal intercostal muscle contract
  • ribs moves downwards and inwards
  • diaphragm relaxes and arches upwards
  • volume of thorax decreases
  • air flows out lungs


The Alveoli

  • gaseous exchange takes place between the air sacs and the blood


Gas Exchange between the alveolar space and the blood

  • the O2 from the air sac diffuse into the moist layer-increases the concentration of O2
  • it diffuses through the alveolar epithelium into the blood capillaries
  • Blood continuous circulation maintaining the lower conc O2 in the blood capillaries, so it diffuses into blood capillaries
  • O2 combines with hemoglobin in the red blood cells
  • Oxygenated blood is transported out of the lungs
Diffussion across the alvoeli is enhanced by;
  • thin- shorter distance to diffuse
  • moist- allow gases to dissolve
  • large surface area
  • have a concentration gradient across surface-maintained by movement of air and transport
  • ability of blood to carry oxygen and carbon dioxide



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