• We don’t want to lose water and heat energy.
• High metabolism, meaning high levels of oxygen need to be delivered.
• Larger, multicellular organisms have a smaller SA:V ratio, so they need a specialized exchange system to supply their needs.

• Requirements are proportional to volume. 
• Diffusion is proportional to surface area.
• Rate of diffusion is proportional to 1/Distance Travelled.

• Amoeba.
• Single Cellular.
• Diffusive gas exchange system.
• Large SA:V ratio.
• Thin.
• Permeable.
• Steep concentration gradient.
• Moist.
• Supplies meet demand.

• Large SA:V ratio.
• Moist surface
• Permeable.
• Well ventilated with a good blood supply. The delivery of oxygen and removal of carbon dioxide maintains the concentration gradient.

• The process of bringing fresh air into the alveoli and removing stale air. 
• Maintains the concentration gradient of oxygen and carbon dioxide between the alveoli and the blood in the capillaries (vital for oxygen to diffuse into blood from the alveoli and carbon dioxide out of the blood into the alveoli).

• The process of swapping one gas for another. Occurs in the alveoli. 
• Oxygen diffuses into the capillaries from the air in the capillaries, and carbon dioxide diffuses out of the capillaries and into the air in the alveoli.

• In the nasal cavity.
• Traps dust and bacteria.
• Warms, cleans and humidifies air.

• Found in trachea, bronchi and bronchioles.
• Keeps the airway from collapsing. The C-Shape allows flexibility.

• Found in trachea, bronchi and bronchioles.
• Secretes mucus to trap dirt.

• Found in trachea, bronchi and bronchioles.
• Sweeps mucus to the back of the throat, to be swallowed.

• Found in trachea, bronchi and bronchioles.
• Contract in response to irritants, restricting the airway.

• Found in trachea, bronchi and bronchioles.
• Recoil to dilate the airway.

• Found in alveoli
• Large surface area for gas exchange. Contains elastic tissue which allows expansion in inspiration.

• Found in alveoli
• Single layer of flattened cells. Thin, for short distance to diffuse. 

• Found in alveoli
• Secrete surfactant. Rich in phospholipids. Detergent-like to lower the surface tension to prevent alveoli from sticking together. When inhaling, inner surfaces of the lung are likely to touch. Cohesive water could make the lung stick together. The surfactant breaks down the bonds, acting as a detergent. 
• Surrounded by capillaries to maintain the concentration gradient.

• Found in pleural membranes.
• Secretes pleural fluid to lubricate the lungs

• Intercostal membrane.
• Work antagonistically to move the rib cage in, out, up and down.

• Found in daphragm.
• Contract and relax to increase and decrease the volume in the thorax.

• Cilia at the top.
• Open topped goblet cells.
• Ciliated cells in-between.
• Wandering cells floating around.
• Capillaries line the bottom of the cells.
• Connective tissue at the base holds the structure together.
• As air flows down toward the lungs, via the trachea and bronchi, the epithelium cells which line them remove particles from the air. Mucus is secreted by goblet cells and swept to the back of the throat by the cilia.

• Diaphragm and external intercostal muscles contract.
• Ribs move up and out.
• Thorax volume is increased.
• The air pressure in the thorax is decreased to below atmospheric pressure.
• Pressure gradient is established from the atmosphere to the alveoli.

• Diaphragm relaxes.
• Internal intercostal muscle contract.
• Ribs move down and in.
• Thorax volume is decreased.
• The air pressure in the thorax is increased to above atmospheric pressure.
• Pressure gradient is established from the alveoli to the atmosphere.

• 100-300 micrometers in diameter.
• 1 squamous epithelium cell thick.
• Covered in an extensive network of capillaries.
• Elastic fibres to stretch / recoil to expel air, without damage.
• Water diffuses from the alveoli cells to the alveoli, keeping them moist. Oxygen dissolves into the water before diffusing through the alveolus into blood.
• The surfactant in the water reduces surface tension and the risk of alveoli collapsing.

• Mainly effects premature babies. Affects 1% and is the leading cause of death.
• They haven't yet produced surfactants sufficiently.
• They’re put on a ventilator or given artificial surfactant to reduce their time on the ventilator.

Residual volume + Vital capacity

• Approximately 5dm³ in humans.

• More frequent and deeper inhalation.
• Quicker ventilation rate (tidal volume X number of breaths per minute)
• Athletes will have a larger vital capacity.

• Smooth muscles of the bronchial tubes spasm, thicken and tighten.
• Air passage becomes enflamed and mucus filled, trapping air.
• Bronchodilators are inhaled, making the muscles relax and expand.
• Steroids may be taken to reduce inflammation.
• More difficult to breathe out - wider, shorter spirometry trace.

• Walls of alveoli lose elasticity and remain filled with air during exhalation, meaning the lungs are permanently inflated.
• Bronchi unaffected.
• Walls of alveoli breakdown and alveoli merge, reducing volume and surface area overall.
• Less gas exchange.
• Caused by longterm irritation and is incurable / irreversible.

• Sticky, brown and stains teeth, fingernails and lung tissue.
• Contains carcinogens.
• Main cancer causer in cigarettes. Every 15 cigarettes causes a mutation. Smoking causes 4/5 cases of lung cancer.

• Stimulate the enlargement of goblet cells, and the production of larger amounts of mucus.
• Paralyzes ciliated cells, so cannot sweep away excess mucus. Smoker cough.
• Chronic bronchitis - swollen and irritated respiratory passages, increased mucus production and damaged lungs. Smoking causes 8/10 cases. Others irritants or genetics.

• C₁₀H₁₄N₂
• Natural liquid alkaloid.
• Comes from tobacco plants.
• Cigarettes contain 8-20mg, but only 1mg is absorbed into the body.

• Inflame blood cells; constrict blood vessels; promotes tumour growth; promotes lung cancer; difficulty breathing.
• Adrenaline rush; rapid heart rate; increased blood pressure; excess glucose in blood; shallow, rapid breathing.

• Colourless, odourless and poisonous, caused by the incomplete combustion of gas.

• Blood combines oxygen-carrying haemoglobin to form carboxyhaemoglobin.
• Heart must work harder, as the oxygen-carrying capacity is reduced by up to 10%.
• Less strenuous exercise must be performed; breathlessness; death; arteries harden; alveoli walls break down and holes are formed.