Gas exchange

• Compensation point


  The light intensity where the rate of photosynthesis exactly matches the rate of respiration. At this point, the uptake of carbon dioxide through photosynthesis is exactly matched to the release of carbon dioxide through respiration, and the uptake of oxygen by respiration is exactly matched to the release of oxygen by photosynthesis.
• Adaptation of the leaf

  for Gas Exchange - Broad


  Large surface area for diffusion

  = increased diffusion of CO2 and O2 (gas exchange).
• Adaptation of the leaf

  for Gas Exchange - Thin


  Short diffusion path

  = faster rate of diffusion of CO 2 and O 2

  (gas exchange).
• Adaptation of the leaf

  for Gas Exchange - Many stomata


  Free unhindered diffusion

  = increased diffusion of CO 2 and O 2

  (gas exchange).
• Adaptation of the leaf

  for Gas Exchange - Internal air spaces

  Allows space for diffusion of gasses inside

  the leaf and increases surface area

  = increased diffusion of CO 2 and O 2 across

  the surface of the spongy mesophyll cells

  (gas exchange).
• Adaptation of the leaf

  for Gas Exchange - Moist internal surface


  Allows gases to dissolve

  = absorption and release of gas from the

  leaf cells.
• Role of stomata

  Stomata allow gases (carbon dioxide and oxygen) to diffuse into and out of the leaf. However, water vapour also diffuses out of the leaf when the stomata are open. To reduce water loss through the stomata, when an external supply of carbon dioxide isn’t needed, guard cells become flaccid causing the stomata to close.
• Adaption of the alveoli - Moist surface


  Allow gases to dissolve

  before they diffuse across

  the cell membrane. (The

  oxygen must first dissolve

  before passing across the

  membrane).
• Adaption of the alveoli - Thin walls


  Short diffusion path

  between the blood and

  ventilated air.
• Adaption of the alveoli - Large surface area


  Increased space / surface

  for gas exchange.
• Adaption of the alveoli - High ventilation and rich blood supply


  Maintains a steep C02 and O2

  concentration gradient

  between the ventilated air and

  the blood.
• Inhalation

  External intercostal muscles contract, internal intercostal muscles relax, ribs move up and out, diaphragm contracts and flattens, volume of thorax increases, pressure in thorax decreases, air is drawn into the lungs.
• Exhalation


  External intercostal muscles relax, internal intercostal muscles contract, ribs move down and in, diaphragm relaxed and returns to its domed shape, volume of thorax decreases, pressure in thorax increases, air is drawn out of the lungs.
• Addiction


  A condition caused by nicotine found in tobacco. Acts as both a stimulant and relaxant, therefore affecting people's moods.
• Bronchitis


  A condition caused by tar found in tobacco. Tar coats the cilia in the tubes of the lungs making it difficult to clear mucus that contains trapped bacteria and dust. Sticky mucus builds up in the lungs causing a thick cough and lung infections.
• Emphysema


  A condition caused by excessive coughing as a result of the build-up of tar. Excessive coughing causes the lining between alveoli to breakdown resulting in reduced alveoli surface area. This results in shortness of breath as a result of the difficulty in absorbing enough oxygen into the blood.
• Cancer


  A condition caused by tar within tobacco. Tar contains chemicals called carcinogens. Carcinogens cause cells to divide uncontrollably.
• Circulatory system disease

  A condition caused by nicotine and other chemicals within tobacco. Nicotine increases blood pressure since it acts as a stimulant. Other chemicals in tobacco cause thickening of blood vessel lining with cholesterol resulting in blocked blood vessels and clots, potentially resulting in a stroke or, when coronary blood vessels become blocked, coronary heart disease.
• Carbon monoxide poisoning

  Carbon monoxide replaces oxygen in red blood cells. If too little oxygen reaches cells, they cannot respire and they start to die.