• Breathing is part of oxygen.  Your body takes in air through the lungs.  
• When you breathe, the diaphragm, which is located under the lungs, goes down and the lungs fill up.
• Lungs are full of small passageways like a sponge in which they can absorb oxygen and they release it.  
• Your body breathes more when you're awake than when you are asleep. 
• Your lungs have just as much surface area as a tennis court.  
• Lungs are full of passageways, little sacs called alveoli.  
• The right lung is bigger than the left, and this is because the heart is located behind the left lung and needs to be able to fit in the chest.  
• The right lung is divided into three parts and the left lung is divided into 2 parts.

• Nares are the openings to the nose.  
• The nasal cavity is lined with cilia, mucous membranes, and blood capillaries.  
• Air is filtered by cilia, moistened by mucous membranes, and heated by blood.  
• The epiglottis closes the larynx to prevent food and water when swallowing to enter the trachea and interfere with your breathing.  

Step 1: Oxygen enters through the nose and mouth.

Step 2: Connected to the nose is the pharynx, or the throat.  From the nose, oxygen flows through the pharynx.

Step 3: The larynx, the voice box, connects the pharynx to the trachea.

Step 4: The trachea is the windpipe.  This connects the larynx to the bronchus.

Step 5: Bronchi divide into secondary and tertiary bronchi.  The main tubes run from the trachea to the bronchioles.

Step 6: Tertiary bronchus lead into the lungs.

• Cellular respiration is the act of cells taking in oxygen, then releasing ATP's and carbon dioxide. 
• When you hold your breath, your cells are filling up with carbon dioxide.  The longer you hold your breath, the more carbon dioxide fills your cells.  The filling of carbon dioxide makes you want to breathe so you can get oxygen in your bloodstream. 

• You breathe in 10 quadrillion molecules of air every time you take a breath.  
• Germs can pass easily through the air.  Mucus membranes surround the pharynx and both lungs.  The mucus membranes protect dirt particles from entering the respiratory system.