Energy flows in one direction through an ecosystem. A food chain shows the transfer of energy from producers to consumers. A freshwater stream food chain: algae aquatic insects crayfish trout Note: all food chains start with a producer!
A food web links all the food chains in an ecosystem together. Each step in a food chain or web is called a trophic level. ◦ Producers always make up the first trophic level. ◦ Consumers make up the second and higher trophic levels. ◦ Each trophic level depends upon the level below it for energy.
Ecological pyramids show relative amounts of energy or biomass contained within each trophic level. Only 10% of energy is transferred to the next trophic level. ◦ Most of it is used for life processes and is lost as heat.
Pyramid of Numbers The relative number of individual organisms at each trophic level decreases. Biomass Pyramid The greatest biomass is at the base of the pyramid. Energy Pyramid Only 10% of the energy available at a trophic level is transferred to the next level. Much of the energy is lost as heat. Section 3-2 Ecological Pyramids
Unlike the one-way flow of energy, matter is recycled within and between ecosystems. ◦ Water, carbon, nitrogen and phosphorus are some nutrients that are cycled.
Evaporation, transpiration, condensation, and precipitation cycle water between the earth and the atmosphere.
Condensation Seepage Runoff Precipitation Transpiration Evaporation Root Uptake Section 3-3 The Water Cycle Water Cycle
Carbon is cycled through carbon dioxide in the air, carbonates and fossil fuels in the ground, and organic molecules in living things. ◦ Respiration, decomposition, and burning release CO 2 into the atmosphere. ◦ Photosynthesis removes it and converts it to organic molecules. Note: only photosynthesis can remove a significant amount of CO 2 from the atmosphere.
All organisms need nitrogen to build proteins. 80% of air is nitrogen. Nitrogen–fixing bacteria living in certain plant roots use atmospheric nitrogen to make nitrates. Producers absorb nitrates and make proteins. Consumers eat producers and get protein. Everybody dies. Decomposers return nitrogen to the soil and air.
Organisms need phosphorus for molecules such as DNA, RNA and ATP. Phosphorous is found mostly in rock, soil and ocean sediments as phosphate. Plants take in phosphates to make needed compounds. Consumers eat producers and obtain phosphates. Everyone dies and decomposers return phosphates to the soil.
The availability of certain nutrients limits the primary productivity of an ecosystem. ◦ Primary productivity is the rate at which organic matter is made by producers. ◦ Farmers apply fertilizers to boost productivity. Fertilizers usually contain nitrogen, phosphorus and potassium.
Limiting nutrients will limit the growth of producers. ◦ Phosphorus limits plant growth in freshwater. ◦ Nitrogen limits plant growth in saltwater. A large input of either of these results in an “algal bloom”. What causes a large input of these nutrients?
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