Earth Science Life Science Physics Chemistry Earth Science Items in the earth science category measure students' knowledge of the scientific principles related to earth features, earth processes, and the earth in the universe. In the Water Cycle question, students were asked to demonstrate their understanding by drawing a diagram. Internationally, students found this item to be rather difficult, with fewer than one-third of the responses showing a fully correct drawing. The next example was the most difficult earth science item. The most common misconception, chosen by more than 50 percent of students, was that oxygen is the most abundant gas in air.
Air is made up of many gases.
Arrow symbol indicates correct answer. Internationally, fewer than half of the students selected the correct response about insect features. The heart rate question required students to design and communicate a scientific investigation. Fully correct responses described a procedure in which the pulse is measured at rest using a timer or watch, the individual engages in some type of physical activity, and then the pulse is remeasured during or after the exercise. Across countries, students found this item to be quite difficult, with only 14 percent of eighth-grade students, on average, providing a fully correct extended response.