-Every respiratory system shares two requirements: a respiratory surface and moist environment.
-Carbon dioxide is the waste product of cellular respiration.
-Skin respiration is the exchange of gases across the skin of the animal.
-Gills are feathery structures made up of many fine filaments lined with capillaries.
-Adjacent to the gills is a network of tiny cappillaries that absorb oxygen and release carbon dioxide from the animal's circulatory system.


-The muscles between the ribs are called the intercostal muscles. All the ribs are connected to the spine and the rib above it except the last two.
-The diaphragm separates the lungs and the heart from the organs in the body.
-The bronchi in the lungs divide twenty times creating bronchioles. The bronchi are reinforced as well.
-The trachea is flexible and strong and approximately 10-13 cm long and 2.5 cm in diamater. It is strengthened by C-shaped cartilage rings.
-Air travels through the nose and mouth, pharynx, epiglottis, larynx, trachea, bronchi, bronchioles, and end in the alveoli.


-Breathing is the mechanism by which mammals ventilate their lungs whereas respiration is the metabolic process by which an organism obains energy.
-The intercostal muscles and diaphragm contract to expand the ribcage and increase the volume of the thoracic cavity.
-Lowering the pressure in the thoracic cavity causes the lungs to expand and fill with air.
-Tidal volume is the volume of air that moves in and out of the lungs during normal breathing.
-The amount of air that remains in the lungs after a full exhale is called residual volume.


-After gas exchange any carbon dioxide left in the blood is carried to the brain where it passes through the medulla oblongata which will increase the breathing rate if necessary.
-Hypoxia, or altitude sickness, results from lower air pressure and symptoms include lack of energy, shortness of breath, headaches, and nausea.
-Fresh water washes away the lipoprotein lubricating film that coats the alveoli causing them to collapse and ending gas exchange.
-Carbon monoxide is toxic because it binds to oxygen receptors in red blood cells about two hundred times more tightly than oxygen does.
-Airborne pollutants including molecules like carbon monoxide, nitrogen oxides, chlorine, and methane, as well as dust and other compounds can cause problems like asthma in which the bronchial tubes suddenly constrict making breathing difficult.


-Like animals, plants must respire to supply their cells with oxygen and remove waste carbon dioxide.
-As long as the soil is sufficiently aerated and contains water, oxygen will diffuse from the air into the air spaces of the soil then into the moisture film surrounding the soil particles and root hairs.
-The guard cells allow the pore to be opened to permit the exchange of gases or closed to prevent the loss of water.
-Lenticels are an arrangement of cells that provide openings from the environment into the tissue of the stem.
-Oxygen diffuses through the stomata ot lenticels into the intercellular airspace of the plant, and from these air spaces can reach every cell in the stem.