Hint: Producers are photosynthesizing organisms meaning any kind of green plant that make their food by taking sunlight and using the energy. So, only producers can convert light energy into usable form of energy and other organisms use the energy, which is made by producers. If there were no producers, there will be no energy for any living thing.
In this question we have asked what would happen if there were no producers. So, first of all what are producers? As we already mentioned that they are the organisms that make their own food that is why they are also known as Autographs. They take energy from the sun and with the help of water convert that energy into food, which is also a form of energy.
The ecosystem has three major biotic components. Producer, consumer and decomposer. They are interrelated and dependent on each other. Producers are the autotrophs or plants which act as a source of food and energy for the consumers by making their own food and consumers eat them as their food for energy. If there were no producers, there is no way to change heat energy from the sun into usable energy. The consumer will not survive because of lack of food and energy. The other dependent animals or trophic level will not survive without food. Without plants and animals decomposers will die and there will be no life on earth. So, if there were no producers, the food chain would not initiate and all the living species on earth would die. Let's take an example, Grass is the producer. If there were no grass, the consumers that feed on it - goat, insects and slugs - would have no food. They would starve and die. All the other animals in the food web like lion, wolves would die too, because their food supplies would have gone.
Note: An ecosystem can exist without consumers but no ecosystem can survive without producers and decomposers because producers are the primary part of the food chain as they produce energy for the whole ecosystem, even if there will be no ecosystem or life without producers and imagine what would happen if there were no decomposers. Wastes and the remains of dead organisms would pile up and the nutrients within the waste and dead organisms would not be released back into the ecosystem.