Gas exhange-

• Gas exchange in non-humans (animals)

  The process of taking valuable oxygen to the cells for aerobic respiration and eliminating Carbon dioxide, which is the waste product of aerobic respiration
• Purpose of gas exchange

  To promote aerobic respiration in order to get energy as ATP
• Types of respiration in animals

  • Diffusion
  • Mucus
  • Tracheae
  • Gills
  • Lungs
• Diffusion

  • Respiration through skin, no organs necessary, organisms' plasm membranes are permeable to oxygen and carbon dioxide, example organisms are Hydra and Tardigrade
• Mucus

  • Absorbs oxygen and excretes carbon dioxide through their skin, skin is flooded with mucus, example is Earthworms
• Tracheae

  • In arthropods such as grasshoppers, a well-developed respiratory system of tubules that open to the outside of the body, allows air to directly reach cells
• Gills

  • Exchange carbon dioxide to get oxygen with the help of a counter current, a counter current is formed between the fish's blood and the water entering
• Lungs

  • Vertebrates evolved a respiratory system involving lungs and bronchi, also have air sacs called alveoli to take in oxygen and eliminate carbon dioxide
• Gas exchange in plants

  When organisms swap gases with the air or water around them
• Respiration

  A chemical reaction that releases energy from glucose, oxygen taken in, carbon dioxide given out
• Photosynthesis

  A chemical reaction that produces glucose from carbon dioxide and water, carbon dioxide taken in, oxygen given out
• During daytime

  Photosynthesis rate is higher than respiration rate, plants take in carbon dioxide and release oxygen
• During nighttime

  Respiration rate is higher than photosynthesis rate, plants take in oxygen and release carbon dioxide
• Palisade tissue

  • Specialized to collect sunlight, complete photosynthesis and produce glucose
• Sponge tissue

  • Specialized to allow gases to move between the outside of the leaf and the photosynthesizing palisade tissue
• Stomata

  • Holes in the bottom of the leaf for gas exchange
• Guard cells

  • Responsible for opening and closing the stomata, open during the day to allow carbon dioxide intake for photosynthesis, close at night to conserve water
• Respiration of plants

  Leaves
• Respiration of humans

  Lungs
• Alveoli in human lungs

  • Millions of air sacs, give the lungs a spongy texture, have a massive surface area of 50-75 square meters, very vascular with thin walls to allow gas diffusion
• Leaves are also very vascular, have a large surface area, and have thin walls to allow gas diffusion like human lungs
• Plants do not have a pumping organ to move fluids, they use diffusion and water pressure instead
• Parts of air that enter the human respiratory system

  • Oxygen
  • Water
  • Other gases like krypton or radon
  • Small and large particles
• Protective mechanisms in upper airways

  • Large dirt particles or insects are stopped in the nasal cavity by nasal hair, small particles are trapped by the nasal mucosa
• Ciliated cells in nasal mucosa

  • Move in a wave-like manner to push nasal mucus towards the pharynx
• Mucociliary clearance

  Small particles caught by nasal mucus are swallowed
• Nasal and oral cavity

  • Warm and moisten respired air, epiglottis closes the larynx during swallowing to prevent food/liquid from entering lower respiratory tract
• Trachea

  • Surrounded by incomplete rings of hyaline cartilage for reinforcement
• Bronchi and bronchioles

  • Bronchi have cartilage, bronchioles have elastic fibers and smooth muscle
• Alveoli

  • Tiny air sacs where gas exchange occurs, composed of thin type 1 pneumocytes and covered in a network of blood vessels
• Gas exchange in alveoli

  Deoxygenated blood enters, oxygen diffuses into blood and carbon dioxide diffuses out, facilitated by red blood cells
• Muscles involved in respiration

  • Neck muscles, intercostal muscles, and diaphragm that inflate and deflate the lungs
• Inhalation/Inspiration

  Lungs inflate, creating negative pressure, we breathe in
• Exhalation/Expiration

  Lungs deflate, creating positive pressure, we breathe out
• Pleura

  • Serves as a lubricant to allow the lungs to shift against the chest wall, has an inner layer covering the lungs and an outer layer lining the rib cage and diaphragm, with a pleural cavity in between
• Trachea branching


  1. Branches into two main bronchi

  2. Main bronchi lead to left and right lungs
• Left lung

  • Has only two lobes (upper and lower)
• Right lung

  • Has three lobes
• Blood circulation

  1. Deoxygenated blood pumped to lungs through pulmonary arteries (blue)

  2. Oxygenated blood returns to heart through pulmonary veins (red)

  3. Distributed to all organs
• Bronchial tree formation

  1. Main bronchi form trunks

  2. Branches into finer and finer branches