It means that it is either an apex predator (if it is a carnivore), or it is simply an animal that is too difficult or dangerous to kill, so no other animal threatens it. For example, the elephant is at the top of the African food chain, mostly because it is the strongest, and no animal hunts it regularly.
A plan to help people ends up harming them Instead
no
when a food chain breaks down, the animals above will not have enough food
top of the food chain
If a component is left out of the food chain then something will not be able to eat it. Then it will die, and the component above it in the food chain will not be able to eat it, and will die. Basically, if a component is left out of the food chain, the food chain collapses.
They die
it because
in a food chain and a food web what shows the movement of energy
Energy
they get eaten by bigger animals.
I think what you are referring to is a food chain, It is a series of energy steps from plants to animals and more animals in the form of food.
Everything in the food chain above them is poisoned as well. The effect is cummulative so the apexial preditors are the most effected.
they die