The following learning goals were used for content analysis in the middle grades science textbook evaluations. Atoms and molecules are perpetually in motion. Increased temperature means greater molecular motion, so most materials expand when heated. In liquids, particles are closely packed, are not arranged regularly, can slide past one another, and attract and are loosely connected to one another. In gases, particles are far apart, are randomly arranged, spread evenly through the spaces they occupy, move in all directions, and are free of one another, except during collisions.
Plants make their own food, whereas animals obtain food by eating other organisms.
Decomposers transform dead organisms into simpler substances, which other organisms can reuse. Matter and energy are transferred from one organism to another repeatedly and between organisms and their physical environment. Several processes contribute to building up and wearing down the earth's surface. Some of the processes are abrupt, such as earthquakes and volcanoes, while some are slow, such as continental drift and erosion. Matching coastlines and similarities in rocks and fossils suggest that today's continents are separated parts of what was long ago a single vast continent.