1: The sun grows the grass, the grass feeds the bongo, the bongo feeds the lion.
2: Yes, because it all cycles around, like other systems.
3: The food web would no longer exist, because it all cycles around, and couldn't if one of it's elements ceases to exist any longer.
4: By consuming other things in the food web.
5: Fat from the food they eat, and energy, also from the food/drink they eat.
6: Matter that is not used in the food web will be used by another element of another food chain at some point.