Some viruses can enter cells by first attaching to the cell membrane. the flu virus targets and attaches to the cells of the nose and mouth. the hepatitis virus targets only specific cells of the liver. state one way the immune system reacts when one of these viruses enters the body ?

stimulus is a change in the environment that causes an organism to react. the response is the reaction to the stimulus. some examples of stimuli for zebras are drought, to many predators, and bad feeding grounds such as dead grass or plants. zebras respond to stimuli just like all other living organisms