Breathing is the process of inhaling oxygen and exhaling carbon dioxide.
Gas exchange is the exchange of gases across the membrane. The processes of breathing and gas exchange are important because the oxygen that is inhaled will be used for energy for the body.

There are two sets of muscles that are involved in the process of breathing. There are the intercostal muscles between the diaphragm and the ribs (can be seen at all the spaces between the lungs and the bones), and the diaphragm muscles located at the area of the diaphragm itself (bottom of the lungs).
Breathing is under subconscious control, meaning we do it naturally without thinking, except when we are doing sports or talking.
As we inhale (breath in), the diaphragm muscles and the intercostal muscles contract. The diaphragm muscles stretches the lungs in a downward motion while the intercostal muscles expand in an up and outwards motion, causing the ribcage to also move in this manner. As the lungs expand, the air inside the lungs expand (because air fills up any 'container' that it is in), which means that the air pressure in the lungs usually drop and since air usually moves from a higher to a lower pressure area, air moves into the lungs. Inhaling is an active process since muscles do contract in the process of the intake of air.
When exhaling, the two sets of muscles relax, and the lungs deflate elastically, reducing the volume inside the lung. As the volume of air inside the lungs decrease, the effect opposite to inhaling happen, which means the amount of pressure inside the lungs builds up. As air moves from higher to lower pressure, it moves out of the lungs. Since the diaphragm muscles relax, it drags down the ribcage, making our chest flatten. Exhaling does not require muscle contraction, therefore is a passive process.
While we are breathing regularly, the two sets of muscles contract at the same time, but sometimes they don't.
When the muscles don’t move in the same pace, the pressure in the lungs change, therefore making hiccups happen. This is why we usually hold our breath or drink water when we have hiccups, to stop the muscles in the lungs from contracting and then resetting the time and pace for these two sets of muscles to contract.


Basically, Gas exchange is when oxygen is delivered from the lungs to the bloodstream and then carbon dioxide from the bloodstream is eliminated. Gas exchange occurs between the alveoli, and a network containing tiny blood vessels called capillaries, located in the alveoli walls. In the process of gas exchange, cells in the body used the oxygen inhaled through the alveoli (in the lungs), and turn them into carbon dioxide and water, the carbon dioxide to be exhaled through the lungs later on. The gases diffuse, moving from higher to lower concentration.
This is a diagram of the blood flowing from the heart to the lungs. As you can see, the red blood cells move from the heart and absorbs the oxygen in the alveolus.
Oxygen molecules are attached to the red blood cells to travel back to the heart; in the meantime, the carbon dioxide molecules in the alveoli are disposed out of the body through the next inhalation. The oxygen then gets transformed into water and carbon dioxide which then comes back into the alveolus, which then gets exhaled.

From this diagram, we can see that the blood picks up the oxygen from the lungs and carry it to the body cell, which made carbon dioxide and water. Most of the oxygen is carried by the hemoglobin (the substance that provides the color red for the blood cell) while the rest is dissolved in the plasma. The plasma also carries the carbon dioxide and the water.
Below is a chart comparing the percentage of different gases when inhaling and then exhaling:

Heres a website that contains a detailed explanaion and animation on Gas exchange. There is also a quiz under for extra revision after watching the animation.

"Animation: Gas Exchange." HIghered.mgnawhill. N.p., n.d. Web. 4 Mar. 2012.

Short video about the Respiratory System and Gas Exchange:

Gas Exchange During Respiration

The Process of Breathing:__

When there is a movement of breathing, the route that air takes looks like this:
Air is inhaled through the nose then is taking the nasal route. The nose humidifies and damps the air before reaching the lungs, and also assists with eliminating redunant particles such as dust and soot using the nostrils. At the end of the nasal route, there is a pharynx. Pharynx is 13cm long and is in a funnel tube shape, which is split into 3 sections. This part of the respiration system broadens the reaer of the nasal cavity, sent down to the second carilage of the treachea. The air proceeds ino the larynx, going through the glottis (cavity in the vocal chords). The larynx protects the food from entering the trachea during digestion. After the larynx, there is a trachea. The trachea is backed up with carilage, which then also splits into two sections called a bronchi. Each of the bronchi is connected to each part of the lung, and is again composed with smaller tubes called the bronchioles. These bronchioles then transport air into the alveoli.

This is a video that will support the paragraph and help understanding with diagrams :)

Chitranshi, Mansi. "Human Respiratory System." Articles Wave. N.p., 25 Feb. 2009. Web. 2 Mar. 2012. <

Mechanism of Breathing. 2011. You Tube. Web. 2 Mar. 2012.


“Gas Exchange.” Penn Medicine. The U of Pennsylvania Health System, 2012. Web. 4 Mar. 2012. <http://www.pennmedicine.org_DisplayAnimation.aspx?gcid=000059&ptid=17>.
Hodgkinson, Wayne. Personal interview. 13 Feb. 2012.

The Human Respiratory System. Youtube//. N.p., 23 July 2008. Web. 26 Feb. 2012.

"The Respiratory System." N.p., n.d. Web. 15 Feb. 2012.
Wright.jerome. "Breathing and Gaseous Exchange." Biologywiz., 10 Sept.
2010. Web. 15 Feb. 2012. <>.