Gas Exchange

• Adaptions of single celled organisms to aid gas exchange

  1. Large surface area

  2. Thin surface

  3. Short diffusion pathway
• Adaptions of fish for gas exchange

  1. Gill fillaments + lamellae provide large surface area for gas exchange

  2. Many capillaries maintain diffusion gradient

  3. Counter-current flow
• Describe counter current flow

  1. Water flows in opposite direction to blood

  2. Blood always passing water with a higher oxygen concentration

  3. Diffusion gradient maintained throughout length of gill
• Describe gas exchange in insects

  1. Air moves into trachae through spiracles

  2. Oxygen travels down concentration gradient towards cells

  3. Trachae branch off into tracheoles with thin permeables that go into cells

  4. CO2 travels down concentration gradient towards spiracles to be released

  5. Rhythmic abdominal movements move air in and out of spiracles
• Describe adaptions to aid exchange

  1. Animals with high SA:V ratio lose more water

  Therefore, adapted kidney to produce less urine

  2. Small mammals in cold regions eat a large amount of high energy foods

  3. Small animals have thick layers of fur or hibernate when it is very cold

  4. Elephants have large flat ears to increase SA for heat loss

  5. Hippos spend lots of time in water to lose heat
• Insect adaptions to reduce water loss

  1. Muscles close spiralces

  2. Waterproof waxy cuticle

  3. Hairs around spiracles

  All to reduce evapouration
• What reduces water loss when plants get dehydrated

  1. Guard cells lose water

  2. Guard cells become flaccid

  3. Stomata close
• Explain the limitations of the gas exchange method for insects?

  Relying mostly on diffusion for gas exchange means the diffusion pathway needs to be short ---> limits size of insects.
• Fossilised insects were much larger. Suggest how the composition of the atmosphere then compares to now.

  Then, [O2] in atmosphere was higher.

  
  

  Short diffusion pathway not as essential as now, as larger [O2] gradient so adequate O2 available for insects to be larger.
• Describe the adaptations of the leaf for gas exchange

  1. Short diffusion path

  
  

  2. Diffusion takes place in gas phase - faster than in water.

  
  

  3. Many small stomata - no cell is far from a stoma and also therefore a short diffusion pathway.

  
  

  4. Many interconnecting air-spaces that occur throughout the mesophyll so that gases can readily come into contact with mesophyll cells.

  
  

  5. Large SA of mesophyll cells for rapid diffusion.
• How do xerophytic plants limit water loss?

  1. Waxy, waterproof cuticle

  2. Reduced number of stomata

  3. Curled leaves with stomata inside protects from wind

  4. Hairs on epidermis traps moist air round stomata

  5. Stomata in sunnken pits that trap moist air reduces concentration gradient
• Describe the structure of the human gas exchange system

  Lungs -> trachea -> bronchi -> bronchioles -> alveoli
• Adaptions of alveoli for gas exchange

  1. Many alveoli = large surface area

  2. Small diffusion distance - alveolar epithelium one cell thick

  3. Good blood supply

  4. Moist
• Inspiration

  1. External intercostal muscles contract, internal intercostal muscles relax

  2. Diaphragm contracts

  3. Rib cage moves upwards and out

  4. Volume of thoracic cavity increases

  5. Lung pressure decreases

  6. Air flows down pressure gradient into lungs
• Exhilation

  1. Internal intercostal muscles contract, external intercostal muscles relax

  2. Diaphragm relaxes

  3. Ribcage moves downwards and inwards

  4. Thoracic cavity decreases

  5. Air forced down pressure gradient out of lungs
• Why does rapid diffusion take place in humans?

  1. RBCs slowed as they pass through pulmonary capillaries ---> more time for diffusion.

  
  

  2. Distance between alveolar air and RBCs reduced ---> RBCs flattened against the capillary walls.

  
  

  3. Capillary endothelium and alveolar epithelium walls are thin (one cell thick) ---> short diffusion distance.

  
  

  4. Alveoli and pulmonary capillaries have a very large total SA.

  
  

  5. Constant ventilation by breathing movements and constant circulation of blood by the heart ---> ensure a steep [O2] / [CO2] gradient for gas exchange.
• Define Tidal Volume

  Volume of air in each breath.
• Define Ventilation Rate

  Number of breaths per minute.
• Forced Expiratory Volume


  The maximum volume of air that can be breathed out in 1 second
• Forced Vital Capacity (FVC)


  The maximum volume of air it is possible to breathe forcefully out of the lungs after a very deep breath in
• Equation for calculating the Pulmonary Ventilation Rate

  Pulmonary ventilation rate = tidal volume x breathing rate.
• Examples of lung diseases

  Pulmonary Tuberculosis

  Fibrosis

  Asthma

  Emphysema
• Describe the formation of Pulmonary Tuberculosis

  1. Tuberculosis bacteria infects lungs

  2. Immune system cells build a wall around bacteria forming small hard lumps - tubercles

  3. Infected tissue in tubercles dies and gaseous exchange surface damaged

  4. Tidal volume decreased

  5. TB also causes fibrosis reduces TV as well

  6. As TV decreases, Ventitation rate increases

  Causing persistant cough, chest pains, shortness of breath, fatigue
• What is fibrosis?

  The formation of scar tissue in the lungs as a result of an infection or exposure to substances like asbestos or dust
• Explain the affects of Fibrosis

  1. Scar tissue forms from infection or exposure to asbestos/ dust

  2. Scar tissue is thicker and less elastic than normal lung tissue

  3. Therefore lungs less able to expand, therefore can't hold as much air, therefore TV and FVC decreased

  4. Reduction in gaseous exchange rate - diffusion slower across thicker scarred membrane

  5. Symptoms = shortness of breath, dry cough, chest pain, fatigue
• Asthma


  A respiratory condition where the airways become inflamed and irritated, usually from an allergic reaction to substances such as pollen and dust
• Describe an asthma attack

  Smooth muscle lining bronchioles contracts + large amount or mucus produced

  This causes constriction of the airways, meaning reduced air flow.

  Therefore FEV1 reduced.

  Symptoms = Wheezing, tight chest and shortness of breath
• Emphysema


  A lung disease caused by smoking or long-term exposure to air pollution, causing foreign particles to become trapped in the alveoli
• Explain emphysema

  1. Foreign particles become trapped in alveoli

  2. This causes inflammation, attracting phagocytes

  3. Phagocytes produce enzyme that breaks down elastin ( protein found in walls of alveoli)

  4. Loss of elastin means alveoli can't recoil air as well + destruction of alveoli walls, reducing surface area for gas exchange

  Therefore less AEROBIC respiration

  Symptoms = Shortness of breath + wheezing
• How to measure volumes of air involved in gas exchange

  Three way taps, manometers, simple respirometers