Which of the following best describes the function for the organelle labelled ‘d’?
(a) moves substances across the cell membrane
(b) transports materials around the cell
(c) controls all cell activities
(d) packages materials for export from the cell

In an experiment examining the effects tai chi on arthritis pain, callahan (2010) selected a large sample of individuals with doctor-diagnosed arthritis. half of the participants immediately began a tai chi course and the other half (the control group) waited 8 weeks before beginning. at the end of 8 weeks, the individuals who had experienced tai chi had less arthritis pain that those who had not participated in the course.