Complex sentence: Irritability takes many forms, from the contraction of a unicellular organism when touched to complex reactions involving all the senses of higher animals; in plants response is usually much different than in animals but is nonetheless present.
Split into simpler sentences: Irritability takes many forms, from the contraction of a unicellular organism when touched to complex reactions involving all the senses of higher animals. In plants response is usually much different than in animals but is nonetheless present.