Final answer:
Disease-causing microorganisms are called pathogens. They can be viruses, bacteria, fungi, or protozoa, some of which causing significant human diseases such as malaria. However, not all microorganisms are harmful; many are beneficial and play vital roles in ecosystems and human health.
Step-by-step explanation:
Disease-causing microorganisms are called pathogens. Pathogens include various types of organisms, such as viruses, bacteria, fungi, and protozoa, which are capable of causing diseases in their hosts. For example, the protozoa responsible for malaria, a major public health concern, can lead to significant mortality, especially in areas like Africa. Furthermore, eukaryotic microbes, which can also be pathogens, exhibit a wide range of life cycles and nutritional needs, contributing to various human diseases.
While it's true that microorganisms can be pathogenic, the majority of them, like most prokaryotes and bacteria, are beneficial and essential to ecosystems. They play roles such as fixing nitrogen, breaking down dead organisms and waste as decomposers, and assisting humans by providing services like fermentation and helping with digestion and immune system training.
Therefore, the best answer to the question "Disease-causing microorganisms are called:" is C. pathogens.