Hint: Photosynthesis is a process by which plants make their food by using water, sunlight, carbon dioxide and chlorophyll. The result of this process is glucose molecules. Plants are autotrophs and hence make their own food.
Photosynthesis is a process that converts light energy into chemical energy. Basically, photosynthesis is the process that provides fuel to plants and that allows plants and even some photosynthetic algae to survive and grow.
If photosynthesis came to a sudden ending, most plants would die within a short span of time. Although, they could hang in there for some time or maybe a few weeks, but that would solely depend on the amount of sugar or "food" that is stored in them. Large trees may be able to hold on for the next few years because of their huge energy stores and also because they use these stores less frequently. However, the majority of plants would have a very sad ending, and therefore, the animals that rely on them would also have the same fate. With all the herbivores dead, the omnivores and carnivores would soon die after them. Although the carnivores might feed on some dead and decayed fleshes, that wouldn't last very long. Sooner or later, these animals would die too.
For photosynthesis to stop occurring, the earth has to undergo complete darkness with no amount of sunlight that could reach the plants for the process. This would cause the earth's temperature to decrease even below the negative 100 degrees Fahrenheit i.e., minus 73 degrees Celsius, resulting in a planet of purely frozen tundra.
Ironically, if the sun shined way too bright, it also could cause photosynthesis to stop occurring. A lot of heat energy would damage plants' biological and chemical structures like the structure of chloroplasts and chlorophyll and prevent photosynthesis from happening. This is the reason for shutting off this process during hot summer days.
Whether the reason is too much sunlight or not enough light, if photosynthesis stopped, plants would stop converting carbon dioxide, an air pollutant into organic material. Today, we rely on these photosynthetic plants, algae and even bacteria to recycle our air. Without them, there would be less or almost no oxygen production.
An artificial photosynthesis process being developed by scientists could just become the world's biggest problem-solver. Using an artificial "leaf", scientists have successfully harnessed sunlight and recreated photosynthesis. The leaf is actually a silicon solar cell that, when put in water and exposed to light, then generates oxygen bubbles from one side and hydrogen bubbles from the other, essentially splitting oxygen and hydrogen.