Question

what happens in the food chain if the frog is missing

Answer 1

If a particular species is missing in food chain then they are linked with other food chains due to scarcity and hence a food web is formed.When frog is missing in a food chain,then the species which frog eats i.e. insects are increased due to less consumption.And species like snakes which depend on frog for their food search for other food sources like rats,gecko etc.
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Answer 2

The producer starts the food chain by capturing solar energy and producing chemical energy stored in the bonds of glucose. You would also see an effect on the consumers of the frogs which are the snakes. They would lose anorganism that they feed on which can cause their numbers to decrease.