Final answer:
The root combining form of 'pathogen' is 'patho-', indicating disease, and 'pathogenic' contains the prefix 'patho-' and suffix '-genic' which means causing. Pneumonia is commonly bacterial, and malaria is a serious protozoan disease, while athlete's foot is caused by fungi.
Step-by-step explanation:
The root combining form of pathogen is patho-, which refers to disease or suffering. In the word pathogenic, the prefix patho- remains the same, and the suffix -genic means "producing" or "causing". Therefore, pathogenic refers to something that can cause disease. The most common disease caused by bacteria is bacterial pneumonia. Two examples of human diseases caused by fungi are athlete's foot and ringworm.
A serious disease caused by protozoa is malaria. Virulence is the ability of a pathogen to cause disease, and highly virulent pathogens are more likely to lead to severe diseases. Common pathogenic bacteria that are part of the normal microbiota of the respiratory tract include Streptococcus pneumoniae and Haemophilus influenzae, which can overcome immune protection with various virulence factors such as capsules and toxins.