People, animals, plants, and fungi all get diseases. Pathogens caused them. Pathogens are things such as a bacteria and viruses. They enter living things and caused them to get sick and sometimes to die. But living things have defenses against pathogens. These defenses are found in their immune systems. There are two types of immune systems, innate and adaptive. First, let's examine the innate immune system. An innate immune system in a living thing is always active. IT's an organism’s first line of defense against diseases. Let's think about humans shall be the skin is our first defense. How well it prevents many things from entering the body. Also, the mucous in the nose prevents airborne foreign bodies, many of which are harmful from entering the body. What else? There were defenses in the body as well. For instance, both the stomach and intestines produce acids. Some of them are able to remove pathogens from the food we eat. There is another important defense inside the body. These are white blood cells. When pathogens enter the body, white blood cells move to fight them. IT's like, uh, like their soldiers fighting an invading army, the white blood cells going where the pathogens are. They attack the pathogens and try to remove them from the body. As you can guess, they're extremely useful, how about some innate systems and other animals and plants? Let me give you some specific examples of them.