27. Are chloroplasts "inside" or "outside" the cell in the sense mentioned previously for mitochondria? What symbiotic origin has been suggested for chloroplasts?

28. What are lysosomes? What types of biochemical reactions occur within them?

29. What are peroxisomes? What very ancient enzyme do they carry? What is the present function of this enzyme? In what sense might the ancestors of peroxisomes have been made obsolete by mitochondria?