Apicomplexa is a group of tiny, single-celled organisms known for their complex life cycles and ability to cause diseases in animals and humans. They are primarily parasites, meaning they live off other organisms, often leading to illness. Some well-known members of this group include Plasmodium, which causes malaria, and Toxoplasma gondii, which can infect cats and humans. These organisms have unique structures that help them invade host cells, making them effective parasites. Apicomplexa reproduce in various ways, including asexual and sexual reproduction, allowing them to adapt to different environments and hosts. Understanding these organisms is crucial for developing treatments for the diseases they cause.