The Roses（罗斯一家）like having picnics on Sundays. This Sunday they want to go to the Red Park. Jack and Mike, their sons, get up early in the morning. Jack puts on a shirt and jeans, and Mike puts on a T-shirt and jeans. They also put on their running shoes. After that they help their mother put bread, milk, eggs and some fruit in a basket and carry it to the car. Mrs. Rose also takes four glasses of juice with her. The little dog Jerry is running after her. It wants to go with them, too. They are all very happy.

动物细胞中的能量转换器是____．