http://www.ck12.org Chapter 1. Human Biology
FIGURE 1.106
This picture shows a one-celled organism calledGiardia lamblia. It is a
protozoan that causes diarrhea.FIGURE 1.107
TheHerpes simplexvirus, which is shown
here, causes cold sores on the lips.
Viruses are extremely small particles.
This illustration is greatly magnified.Several pathogens spread through sexual contact. HIV is one example, which is discussed in the next lesson. Other
pathogens that spread through sexual contact are discussed in a separate lesson.
Many pathogens that cause respiratory diseases spread by droplets in the air. Droplets are released when a person
sneezes or coughs. Thousands of tiny droplets are released when a person sneezes (Figure1.108). Each droplet can
contain thousands of pathogens. Viruses that cause colds and the flu can spread in this way. You may get sick if you
breathe in the pathogens.