Pack 7 - Exchange Part 1

Surface area to volume ratio:
1. Absorption = Large SA
  1. Heat loss = Large SA
Gas Exchange:
1. Respiration is the release of energy from food
2. Gas exchange surfaces need:
  1. A large SA:vol ratio
  2. To be thin
  3. Be permeable to gases
  4. Some cases a ventialtion system
  5. Some cases an internal medium
  6. To be moist
In a dicot leaf
1. Gas exchange in dim light:
  1. Oxygen moves in by diffusion
    1. It then moves by diffusion and dissolves in a layer of moisture
      1. It moves in solution into the cell vacuole
2. Gas exchange in strong light:
  1. Photosynethsis, so oxygen will come out of the cell via diffusion
3. Stomata open in light and close in the dark
  1. when they are open gas exchange is able to occur
  2. If they close the rate of diffusion of oxygen and carbon dioxide is reduced
4. Transpiration is the evaporation of water from a plant
  1. Wind, temperature, light and humidity affect it
5. Limiting water loss
  1. More water is lost from the plant when there is a greater water potential between the inside and outside of the stomata
  2. Xerophyte plants have these adaptions:
    1. Extensive roots
    2. Tissue that stores water
    3. Thick waxy cuticle
    4. Small leaves
    5. Stomata that open at night
    6. Leaves roll up
    7. Hairs on leaves to trap air
In a single celled organism (protoctistan)
1. Oxygen and carbon dioxide diffuse in and out
2. They have a large SA:vol ratio
Gas Exchange in Insecta
1. Insects have a conflict between gas exchange and water conservation
  1. They conserve water by having a waterproof cuticle
  2. For efficient gas exchange insects have spiracles which lead into tracheae which then divide into tracheoles
2. Respiratory gases move in and out by:
  1. Moving along a concentration gradient
  2. Ventilation - insects can increase the movement of air in their tracheae by moving their muscles
3. Tracheoles are very fine tubes that enter all the body tissues of the insect, water from the cells enters the tracheoles by capillarity, gases diffuse slower in a liquid than a gas
  1. Oxygen transport can be facilitated by the production of lactate during intense activity, this decreases the water potential of the cells therefore water moves back into them by osmosis
4. Steps occurring in the insects body during activity:
  1. 1. Anaerobic respiration
    1. 2. lactate increases
      1. 3. Water potential decreases
        4. Water enters muscles by osmosis
        5. Air comes down its tracheoles
        6. Oxygen and carbon dioxide diffuses faster through gases than liquids
        7. Increases respiration
        Water entering the insects muscles means oxygen and carbon dioxide diffuse faster, so more respiration
5. 3 ways an insect cuts down water loss:
  1. 1. Small surface are to volume ration
    1. 2. Waterproof coverings
      1. 3. Spiracles
Gas exchange in Bony Fish
1. Bony fish have four pairs of branchial arches supporting gill lamellae
  1. These are covered by a muscular flap called the operculum
2. How it happens:
  1. 1. Fish open their mouth and lower the floor of the buccal cavity
    1. 2. This increases the volume and decreases the pressure in the mouth compared to the outside, so water enters
      1. 3. The operculum is closed at this stage
        4. Then the fish closes its mouth and raises the floor of the mouth
        5. This decreases the volume and increases the pressure compared to the outside, so it forces water through the gills and out through the operculum
3. Water has a high density so it's a lot of work for a fish to move it in and out, this is why it takes it in and releases it in the same direction
  1. It also allows counter current
4. Adaptions:
  1. Many gill filaments and gill lamellae (High SA:vol)
  2. Counter current exchange system
    1. Constant diffusion gradient across whole length of gill
  3. Start diffusion pathway between blood and water
    1. Epithelium of lamella are thin
5. Counter current:
  1. The blood and water flow in opposite directions and gives a more efficient system
    1. This is because the blood is constantly meeting new, well oxygenated water
      1. Dotted lines = Oxygen in water concentration
        Red line = Oxygen in blood concetration
Mammalian Lungs
1. Respiration is composed of two processes:
  1. Cell respiration:
    1. It is the process by which ATP is produced
    2. It involves:
      1. The breakdown of food to release energy
        Some of this energy is used to make ATP from ADP
        The rest of the energy is released as heat
    3. Basically it is Glucose + Oxygen --> CO2 + Water + Energy
  2. Gas exchange:
    1. Uptake of oxygen and release of carbon dioxide
      1. Many larger mammals have an increased metabolic rate which increases oxygen demand
        This leads to a specialised gas exchange system and a transport system
    2. To be effective it must be:
      1. Moist
        Permeable
        Large SA:vol
        Maintained concentration gradient
        Thin
    3. Structure and functions of human gas exchange system:
      1. Functions of the larynx:
        Carries air in and out and vibrates voice chords
      2. Role of cartilage in the trachea:
        To keep the trachea open
      3. Role of bronchi and bronchioles:
        Carry air to the alveoli
      4. Structure of alveoli
        Walls are one cell thick and are surrounded by capillaries
        They are used for gas exchange
    4. Alveoli:
      1. made up of squamous Epithelium
        Thin cells - short diffusion distance
        They're flat so a greater surface area
      2. A layer of moisture coats the epithelium in which oxygen dissolves prior to diffusing into the blood stream, a substance (surfactant) reduces the surface tension and prevents alveolar walls being pulled together and therefore collapsing
      3. Macrophages are also present
      4. Partial pressure
        Partial pressure = it is equivalent to concentration
2. Diffusion of oxygen and carbon dioxide
  1. 1. Diffuses through alveolar space
    1. 2. Dissolves in mucus
      1. 3. Diffuses through squamous epithelium
        4. Diffuses through squamous endothelium
        5. Diffuses through plasma
        6. Diffuses through semi-permeable membrane of red blood cells
        Carbon dioxide travels in the opposite direction and both gases are independent of each other
  2. This process may not be efficient because:
    1. Some blood entering the lungs does not go into the alveolar capillaries
    2. Some alveoli are under-ventilated
3. Mechanisms of breathing:
  1. When air is breathed in (inspiration)
    1. Chest is expanded, pressure decreases and is lower than atmospheric
    2. Diaphragm:
      1. Diaphragm contracts and flattens
        Pressure decreases so air comes in and volume increases
    3. Intercostal muscles:
      1. External intercostal muscles contract makes ribs move up and out
        So the pressure decreases and the volume increases
    4. 6 marker for inhalation:
      1. Ext. intercostal muscles contract
        Ribs move up and out
        Diaphragm contracts and flattens
        Volume increases
        Pressure decreases
        Air comes in
  2. When air is breathed out (expiration)
    1. Chest is contracted and makes pressure higher than atmospheric
    2. Diaphragm:
      1. Diaphragm relaxes and creates dome shape
        Pressure increases and air is pushed out, therefore volume decreases
    3. Intercostal muscles:
      1. Internal Intercostal muscles contract cause ribs to move in and down
        So the pressure increases and the volume of air decreases
4. Changes in pressure and volume during volume
  1. Tidal volume = amount of air you breath in and out in one breath
  2. Functional residual capacity = the bit of oxygen always left in the lungs
5. Pulmonary ventilation
  1. Pulmonary ventilation = Tidal volume*Breathing rate
    1. In cm^3min^-1
6. Correlation and causal relationships:
  1. Correlation does not mean causation, there may be other factors (then think of another factor
7. Lung diseases:
  1. Risk factors:
    1. Smoking
    2. Lack of exercise
    3. Occupation
    4. Genetics
    5. Infections
  2. Fibrosis causes scar tissue and reduces elasticity
  3. Asthma causes restricted ventilation
  4. Emphysema causes restricted ventilation, a lower concentration gradient across alveoli cells, longer diffusion distance, due to less elastin produced
  5. Tuberculosis causes scar tissue and can be fatal

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Pack 7 - Exchange Part 1

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