A PLANT IS AN ANIMAL STANDING ON ITS HEAD

The view that plant materials derive from the earth and are absorbed a s food through the roots (which was widely held by scientists until be ginning of the 19th century) is similar intuitive views, which impinge on their learning about photosynthesis. Examples of ways in which an examination of the earth-and-roots historical model can be used to giv e credence to students' prior knowledge and to promote discussion abou t that knowledge, are described.