One technique used to investigate the activity of cell organelles is called differential centrifugation. In this technique, a tissue is homogenised (ground in a blender), placed in tubes and spun in a centrifuge. This makes organelles sediment (settle) to the bottom of the tubes. The larger the organelles, the faster they sediment. By repeating the process at faster and faster speeds, the organelles can be separated from each other according to size. Some liver tissue was treated in this way to separate ribosomes, nuclei and mitochondria. The centrifuge was spun at 1000 g, 10 000 g or 100 000 g (‘g ’ is gravitational force).

a. In which of the three sediments – 1000 g, 10 000 g or 100 000 g – would you expect to find the following?

i. Ribosomes

ii. Nuclei

iii. Mitochondria

b. Liver tissue contains many lysosomes. Suggest why this makes it difficult to study mitochondria using the differential centrifugation technique.