15.7 PRODUCERS, COMSUMERS AND DECOMPOSERS
Organisms can be classified according to their roles as producers, consumers or decomposers.
Producersare organisms that make complex, organic compounds from simple,inorganic molecules. The main producers are green plants and algae, including phytoplankton, which grow in the world’s grasslands, forests, lakes and oceans. In the process called photosynthesis (Module 6.12), they use energy from sunlight to make complex carbohydrates,such as starch (C12H10O5)n,from carbon dioxide (CO2) and water (H2O). Oxygen is produced as a by-product and released into the atmosphere.Producers use the starch, together with minerals from the soil or the surrounding water, to make other complex compounds including sugars, cellulose, lipids and proteins (Module 13.11). The elements absorbed from the soil include everything needed to make complex living tissues; nitrogen, phosphorus, sodium, potassium, magnesium, calcium, iron and chlorine are the most important ones. Producers are the basic source of food for all other organisms.
Consumers are organisms that feed on the complex, organic compoundsmade by producers.They usethese compounds for energy and for building tissues. The main consumers are animals and they all need food that contains carbohydrates, lipids and proteins. Animals that feed on plants are calledprimary consumersor herbivores; they include examples from caterpillars to cattle! Animals that feed on other animals are calledsecondary consumersorcarnivores;they include examples from ticks to tigers. Animals that eat both plants and animals are called omnivores; theyincludeexamples like pigs, rats and crows. Humans are omnivores too. Herbivores have mouth parts and digestive systems adapted for breaking down the tough, cellulose walls of plant cells. Herbivorous mammals have flatteeth for grinding cellulose and long intestines digesting it. Carnivores have mouths and digestive systems adapted for eating meator sucking blood!Carnivorous mammals have sharp teeth and need only short digestive systems.Mosquitoes have sharp feeding tubes that pierce skin.
Decomposers are involved in the decay of organic matter.The main decomposers are fungi and bacteria. When organic matter decays, fungi and bacteria break down complex organic substances into simple inorganic molecules.These are recycledas minerals in soil or water, andas carbon dioxide in the atmosphere.The chartsummarises the main relationships between producers, consumers and decomposers.
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- 1. What are (i) photosynthesis, (ii) producers, (iii) carbohydrates, (iv) cellulose, (v) minerals, (vi) proteins, (vii) consumers, (viii) organic matter, (ix) decomposers?
- 2.What shows us that the liger must be a carnivore?
- 3.Use the chart above to summarise, in 3 sentences, the roles of producers, consumers and decomposers.
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