Science Homework
Due: Friday, December 5
Name: ______________________________________________________________
Teacher: ___________________________
Period: _________
The Respiratory System
The respiratory system brings oxygen from the air into the blood and returns carbon dioxide from the blood to the air.
The respiratory system works very closely with the circulatory system to provide cells with oxygen, and to remove waste
carbon dioxide produced by the activities of cells.
1. The main function of the respiratory system is to____________________________________
___________________________________________________________________________.
Directions: Trace the pathway of air on the diagram as you read the passage below. Follow the directions to make a
color key for the respiratory system.
When you breathe, air enters the respiratory system through the nose. The lining of the nose produces mucus,
which moistens air and traps germs and dirt and is lined with hairs to remove dust and dirt from the air.
2. What is a common name for mucus?_______________________________________________
3. What is the function of mucus in the nose?__________________________________________
Air from the nose travels to the throat, and then goes through the trachea or windpipe. A flap called the
epiglottis covers the windpipe to prevent food and water from entering the trachea.
4. Describe the function of the epiglottis______________________________________________
The trachea branches off into two smaller tubes called bronchi, which lead to a lung through smaller and
smaller branches called bronchioles.
The air then enters the tiny air sacs called alveoli where the blood picks up oxygen and then gets rid of carbon
dioxide.
5. The tiny sacs in the lungs where oxygen and carbon dioxide enter and leave the lungs are called
______________________________.
The lungs do not take in air by themselves. Breathing is caused by the actions of muscles in the ribs,
diaphragm, and abdomen to draw in oxygenated air by making the chest cavity larger. As the chest cavity gets
larger, the air pressure gets lower inside the chest and lungs. Air rushes into the lungs to equalize the air
pressure. We breathe out carbon dioxide when the ribs move in and the diaphragm moves upward. This
makes the chest cavity smaller which forces out of the lungs because of the increase in air pressure. All of
these actions take place without us thinking about it, because breathing is an involuntary action controlled by
the nervous system.
6. Muscle contractions in the _________________, ___________________ and ___________________ cause
us to breathe in and out.
7. Another word for breathe in is ______________________________.
8. Another word for breathe out is _____________________________.
Once in the lungs, the oxygen in the air passes across the thin membranes of the alveoli sacs in the lungs, and
into the alveoli sacs in the lungs, and into the oxygen-poor blood in the tiny capillaries that surround the sacs.
The thin-walled capillaries are so narrow that they can hold red blood cells in a single line.
9. Alveoli sacs are surrounded by __________________________________ which are so narrow (thin) they
can hold____________________________________________________________.