3. How does the photosynthesis of cyanobacteria differ from that ofthe photosynthesizing green sulfur bacteria?(10分)

4. In animals, the cell cycle is controlled by a molecular control system which involves cyclic changes of regulatory proteins. As well, it is regulated at certain checkpoints (G1, G2, and M) by both internal and exterrnal signals. Please describe in details exactly how is the cell cycle regulated? (9 points)