Step-by-step explanation:
Food chain is linear sequence of the organisms through which the nutrients and the energy pass as one organism eats the another.
If one species in the food chain ceases to exist, the other members in rest of chain could cease to exist too or may increase in population which can affect other food chains. (Breaking of food chain).
This is because the animals in the food chain are dependent on the nutrient present in the another.
For example in the food chain,
Grass ---- Deer ------ Lion
If all deer extinct, the lion will die as they will have nothing to feed on and the population of grass increases.