Tropisms are growth responses of plants to environmental stimuli. They can be classified into two main types: positive tropism, where a plant grows toward a stimulus, and negative tropism, where it grows away from one. Common stimuli include light, gravity, and water. For example, phototropism is the growth of a plant toward light, while gravitropism refers to how roots grow downward in response to gravity. These responses are crucial for a plant's survival and development. By adapting to their surroundings, plants can optimize their access to resources like sunlight and water. Understanding tropisms helps scientists learn more about plant behavior and ecology.