Nutrition and Food Chains
Food Chains
A food chain should be very simple, something you have been studying since primary school; but now we'll take it to the next level.
A typical food chain chain looks like this:
A food chain shows how energy is transfered between organisms
The energy comes as solar energy that plants use to convert into chemical energy (photosynthesis). The herbivores eat the plants, taking some of the energy and then they are prey and the energy is transfered to the predator.
But some of this energy is lost at each stage (or trophic level). In the above example, the grass looses some energy by respiration. And then the rabbit loses energy by heat and waste. And so by the time it gets to the fox a fraction of the original energy gets to it.
Pyramids
A food chain can be represented quantatively (with numbers) in the form of a pyramid of numbers, is is one for the previous food chain:
From this graph we can see there are fewer foxes than rabbits; which makes sense because a fox must eat several rabbits to get enough energy in order to survive.
However! A pyramid of numbers does have its drawbacks. In the following example you will see why.
A large number of aphids feed on a single oak tree and so the base of the pyramid is just as wide as the top.
To rectify this problem you can draw a pyramid of biomass. This represents the mass/weight of each trophic level. And since an oak tree is much larger than the aphids that live on it, the balance is restored.
Food production
The energy transfer through a food chain can be maximised for food production. For example, in farms. This is called intensive farming.
A farmer can get the most energy from a crop of wheat, for example, by using fertilisers - supplying them with the minerals they need to grow.
In a natural environment, the wheat would be eaten, but this removes energy. So pesticides are used to remove pests. Similarly disease must be prevented in order that the farmer get the highest yield possible and ultimately earn the most money possible.
