Final answer:
Plants can undergo innate and adaptive immune responses in the first line of defense. The innate response is quick and nonspecific, while the adaptive response is more specific and takes longer to develop.
Step-by-step explanation:
The two types of immune responses that plants can undergo in the first line of defense are innate and adaptive. The innate immune response is a quick but nonspecific response to pathogens, while the adaptive immune response is more specific and takes longer to develop. In the innate response, plants have physical barriers such as the cell wall and chemical defenses. In the adaptive response, plants activate specific defenses that are transportable within the organism and retain information about earlier infections.