Proteins that regulate the cell cycle are inactive when the cell is not dividing, and they are turned on when the cell begins the cell cycle. What would happen if these proteins remain turned on indefinitely?

If these proteins turned on indefinitely than the cell will divide uncontrollably and will become a cancerous cell.

Explanation:

The cell cycle is controlled by many proteins which helps in the regulation of cell cycle and cell cycle completion. So these proteins are inactive when cell is not dividing but become active when cell is dividing which means they are needed to be active to divide the cell.

Therefore if they remained turned on indefinitely than the cell will continue to divide indefinitely like cancerous cells and due to overproduction of cell it will cause tumors or cancer in the body.

If there is no sunlight the plants will die. Then because of dead plants the herbivores will die and so on. the food chain will be very disrupted.