Students measured the biomass of a community living in leaf litter under the trees in the school conservation area. They found woodlice feeding on the leaves, ground beetles feeding on the woodlice and centipedes feeding on the beetles. Each student weighed the leaves in their sample and the other organisms and put their results together with the rest of the class. Which of the following could represent the class results in order of the food chain starting from the leaves?

Apart from the extremophiles (some of whom get their energy from chemicals and heat coming from deep-sea hydrothermal vents), animals are solar powered! How come? The answer is food chains. Food chains are concerned with the transfer of chemical energy as biomass to the top predator. They always begin with plants and end with a carnivore and they can be combined into food webs. A food web describes the feeding relationships within a community of plants and animals. A food chain can be represented as a pyramid of biomass (mass of living material) by drawing a pyramid style of histogram. Each... Show more

Apart from the extremophiles (some of whom get their energy from chemicals and heat coming from deep-sea hydrothermal vents), animals are solar powered! How come? The answer is food chains. Food chains are concerned with the transfer of chemical energy as biomass to the top predator. They always begin with plants and end with a carnivore and they can be combined into food webs. A food web describes the feeding relationships within a community of plants and animals.

A food chain can be represented as a pyramid of biomass (mass of living material) by drawing a pyramid style of histogram. Each trophic (feeding) level is drawn to the same scale. The lowest level of the food chain normally has the highest biomass whilst the top predator has the lowest biomass. The reason for this is that energy and materials are lost at each stage of the food chain. Let's consider a simple 3 step food chain to see how this works. 

The start of a food chain are the plants living in the community. They absorb the Sun's energy and use it for photosynthesis. During photosynthesis, some of the food (glucose) they produce is used to release energy in the process of respiration and some is used to form the biomass of the plant.

Herbivores eat the plants. Some of the energy from the plants they eat is used immediately for respiration and therefore lost from the food chain. Some is stored in the body or used by the body for growth, repair or both, this keeps the biomass in the food chain. The herbivores excrete waste material which lessens the amount of biomass in the system. 

Next in the food chain is a predator. This hunts and eats the herbivores. As it hunts, a lot of the energy from its previous successful kill is used up and lost from the food chain. More is lost as the predator excretes its wastes. Only a proportion of the energy from eating the prey remains in the predator.

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