The diagram illustrates the important role that microbes, play as primary producers and in the cycling of nutrients.Photosynthetic organisms are capable of using light energy which is trapped by chlorophyll, to convert carbon dioxide and water into oxygen and glucose (food). This process is called photosynthesis. Organisms that make their own food are called primary producers and are always at the start of the food chain. Animals and micro-organisms like fungi and bacteria get energy and nutrients by eating other plants, animals and microbes.Organisms release energy from food (glucose), as well as carbon dioxide and water in the process of aerobic respiration. This energy is used to do the work needed to keep cells and organisms alive. Aerobic respiration requires oxygen.The decomposers (fungi and soil bacteria) obtain their energy and nutrients from the dead bodies and waste products of other organisms. As dead bodies and waste products break down, they release essential nutrients into the soil.
As the energy is passed along the food chain much of it is either used or lost. Therefore there is a limit to the number of organisms in a food chain. The top carnivore is usually the third or fourth consumer.
Mercury compounds were used until quite recently to make insecticides and special paints that stop barnacles growing on the hulls of ships.Unfortunately, when it gets into the food chain mercury damages the nervous systems and reproductive systems of mammals (including humans). The diagram shows how mercury can accumulate in the food chain.Tiny plankton in the sea absorb the mercury compounds. When the plankton are eaten by small fish, the mercury they contain stays in the fish. As the fish need to eat a lot of plankton, the concentration of mercury in them becomes higher than its concentration in the plankton.The small fish are eaten by larger fish, and these are eaten by still larger ones, such as tuna fish. This creates a high concentration of mercury in the tuna. People eating contaminated tuna may get mercury poisoning. Mercury is now banned from many chemical products and mercury use in industry is carefully regulated.<DDT is an insecticide that can pass up the food chain from insects to small birds, and then from the small birds to birds of prey, like hawks. It can accumulate in the birds of prey, giving them a large amount of DDT. Concentrations of DDT in birds causes weakness in their eggs, and reduces their population. DDT is now banned because of this.>
Energy Transfers is a Food Chain
Only about 10% of the energy which the plant
used for growth is taken into the body of the
The second consumer uses some of this energy for
its own body activities and some of the energy
will be wasted.
The amount of energy available for the tertiary
consumer is only 1% of the energy which the
primary consumer gained from the plant.
Effects of a Damage
Toxic materials are poisonous.
Some quickly break down into
harmless substances in the
persistent and do not break
down. Instead, they accumulate
in the food chain and damage
the organisms in it, especially
the top predators. Mercury and
DDT are two persistent toxic
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