Question

suppose plants disappear from the Earth what effect it can have on other organisms in food chain

Answer 1

Since plant are the only who convert and trap the sun energy to form food.
If they aren't then the food available to any trophic level is not possible due to which whole ecological balance will be disturbed.

Answer 2

if the plants dissappear from the earth then it will affect the diet of lower animals (herbivores ) and they will start to die and eventually affect the diet of entire animals in food chain and all the animals /organism may die if they do not find any alternative to survive