The energy disappears...
Energy from the sun is the source of energy for nearly all life on earth.
Green plants and algae use a small % of the light energy from the sun to make food during photosynthesis. The energy is stored in the substances which make up the cells of plants and algae. The energy then works its way through the food chain as animals eat plants and algae and then eat other animals.
Respiration supplies energy for all life processes. Most of the energy is eventually lost to the surroundings as heat.
Some of the material that makes up plants and animals is inedible (can not eat it) e.g. bones. So it doesn't pass to the next stage in the food chain. Material and energy are also lost from the food chain in the orgainsms waste materials.
This explains why you get biomass pyramids. Most of the biomass is lost and so doesn't become biomass in the next level up
It also explains why you don't get any food chains with more than 5 trophic(nourishment) levels. So much energy is lost at each stage that there's not enough left to support more oraginsm after 4 or 5 stages
Energy is cycled back to start of the food chain b
living things are made up of materials they get from their surroundings.
Plants take elements like Carbon, Oxygen, Hydrogen and Nitrogen from the soil or the air. They turn these elements into complex compounds like Carbohydrates, fats and proteins that make up living organisms, these then pass through the food chain.
These elements are returend to the environment in waste products produced by orgainsms or when the orgainsms die.
The material decays becuase they are broken down (digested) by microrgainsms.
Microorganisms work best in moist, warm conditions. Most microorganism break down material faster when there's plenty of oxygen avilable. Compost bins create these conditions.
All these important elements are then recycled- return to the soil, ready to be used by new plants and put back into the food chain again.
The materials taken out of the soil and used are balanced by those that are put back in. There's a constant cycle happening.