Which statement is true about protozoa?

Protozoa are single-celled organisms that exhibit a remarkable degree of complexity and adaptability, allowing them to function independently in various environments. This capability means they can live and thrive in diverse habitats, including freshwater, marine, and soil ecosystems, often contributing to the ecological balance. Their ability to function independently is crucial for their survival and reproduction, enabling them to engage in processes such as photosynthesis in some cases or consuming organic matter in others.

The other statements do not accurately reflect the characteristics or roles of protozoa. For example, while some protozoa can reproduce asexually, they also have the ability to reproduce sexually, showing diversity in their reproductive mechanisms. Additionally, certain protozoa are well-known pathogens responsible for diseases such as malaria and amoebic dysentery, indicating that they can indeed cause diseases. The claim that protozoa are essential for plant growth is also misleading, as while they can play supportive roles in certain ecosystems (e.g., nutrient cycling), they are not directly essential for the growth of plants in the same way that other organisms, like nitrogen-fixing bacteria, can be.