The Zimbabwe Secondary School Science Project (ZIM-SCI) developed student study guides, corresponding teaching guides, and science kits for a low-cost science course which could be taught during the first 2 years of secondary school without the aid of qualified teachers and conventional laboratories. This ZIM-SCI study guide presents activities and experiments in a unit focusing on the principles of force, support, and action in living things. Major areas investigated include: purpose of skeletons in living things; three main forms of support in plants; three main types of skeletons in animals; the ways in which bones are adapted according to the medium in which an animal lives; and the method by which stability is maintained in four-legged animals (with reference to the center of mass). Other areas investigated include limbs as "animal machines" (muscles which exert a force on a bone which acts as a lever), muscle action, and the protective function of various parts of the skeleton. Information is provided throughout the unit to help students understand the scientific concepts behind the activities and experiments. (JN)