Ecosystems and the Biosphere

Energy Transfer All organisms need energy to carry out essential functions – growth, movement, maintenance, repair, and reproduction In ecosystems, energy flows from sun to autotrophs to organisms that eat autotrophs to organisms that feed on other organisms. Amount of energy ecosystem receives and the amount. transferred from organism to organism have an effect on the ecosystem’s structure.

Energy Flow Whenever one organism eats another, molecules are metabolized and energy is transferred. Energy flows through an ecosystem from producer to consumer

Trophic level Trophic level indicates the organism’s level of nourishment, or position in the sequence of energy transfer illustration First level – all producers Second level – herbivores Third level – predators of herbivores

Food Chain single pathway of feeding relationship that results in energy transfer to mouse to snake to hawk Feeding relationships in ecosystems are usually too complex to be represented by a single food chain. Many consumers eat more than one type of food and many organisms may feed on the same organisms.

Food Web Models of complex feeding networks within ecosystems; series of food chains interwoven

Energy Pyramid distribution of energy and matter in an ecosystem Shows the distribution of energy in a food chain Energy flows upwards from producers to consumers Energy is lost as head between each tier of the pyramid; average of 10% of energy is passed from one level to the next level

Other Pyramids Biomass pyramid shows the total mass or organisms at each tropic level Less biomass at higher tropic levels than lower levels Pyramid of numbers shows the actual number of organisms present in each trophic level

Water Cycle Crucial to life - ells are 70-90% water 90% of water evaporates from terrestrial ecosystems passes through plants in a process called transpiration – plants take in water through roots and release water and take in CO 2 through the stomata in their leaves In pic to right note: evaporation, condensation precipitation, transpiration

Carbon Cycle Photosynthesis and cellular respiration form the basis of carbon cycle In photosynthesis, plants use carbon dioxide, water, and solar energy to make carbohydrates and produce oxygen Both autrotrophs and heterotrophs use oxygen to break down carbohydrates during cellular respiration

Nitrogen Cycle The most important thing about the nitrogen cycle is that bacteria are involved All organisms need nitrogen to make proteins and nucleic acids. Nitrogen gas makes up about 78% of the atmosphere. Bacteria break down the corpses and wastes of organisms and release the nitrogen they contain as ammonia – ammonification. Bacteria in the soil takes the ammonia and oxides it into nitrites – nitrification. Nitrogen is returned to the atmosphere through denitrification. Plants can absorb nitrates from the soil, but animals cannot. Animals get nitrogen by eating plants and other organisms and then digesting the proteins and nucleic acids.