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Food Chains, Food Webs, and the Transfer of Energy Autotrophs • A groups of organisms that can use sunlight or chemicals to convert water and carbon dioxide into glucose. • In other words, autotrophs are organisms that can make their own food. • Autotrophs are also called producers because they produce all of the food that other organisms use. • Without autotrophs, life on Earth would have become extinct by now. • Most autotrophs are photosynthetic. • Ex. Plants and Algae Photosynthetic Autotrophs Chemosynthetic Autotrophs • Some autotrophs use chemicals available in their environment to make glucose: • These are called Chemotrophs – Chemotrophs get their energy from chemical substances, like hydrogen sulfide. – They live deep in the ocean where there is no sunlight – Ex. Bacteria and some deep-sea worms Heterotrophs • Organisms that DO NOT make their own food. • Another term for Heterotrophs is consumers because they have to consume other organisms in order to live. • There are several kinds of autotrophs, based on what they eat. • Ex. Rabbits, Deer, Mushrooms Heterotrophs Heterotrophs • Herbivores Eat ONLY plants. • Ex. – Cows, Elephants, Giraffes Heterotrophs • Carnivores Eat ONLY meat • Ex. – Lions, Tigers, Sharks Heterotrophs • Omnivores Eat BOTH plants and animals • Ex. – Bears and Humans Heterotrophs • Scavengers and Detritivores feed on the tissue of dead organisms (both plans and animals) • Ex. – Vultures, worms, and pill bugs. Heterotrophs • Decomposers Break down organic molecules and turn them into simple nutrients or fertilizers • Ex. – Bacteria and Mushrooms Food Chains Whenever an organism is consumed by another, energy is transferred into the consumer. • A simple sequence of this type of energy transfer is know as a food chain. • A food chain is simple and direct. • It involves one organism at each trophic level Food Web • Most organisms eat more than JUST one other kind of organism. • When more organisms are involved, we really have several interconnected food chains. • These more complex interconnections are called a food web. Food Web Food Web Notice that the arrows points in the direction of the flow of energy. Trophic Levels • Energy moves from one organisms to another when it is eaten • Each step in this transfer of energy is know as a trophic level Flow of Energy • When a zebra eats grass, it does not get all of the energy that the grass had (much of it is not digested). • When a lion eats a zebra, it does not get all of the energy from the zebra. • No organism EVER receives all of the energy from the organism they just ate • On average, only 10% of the energy from one trophic level is transferred to the next – this is called “the 10% law”. Ecological Pyramid • An ecological pyramid (also called an energy pyramid) shows the relationship between consumers and producers at different trophic levels in an ecosystem. • Shows the relative amounts of energy or matter (biomass) contained at each trophic level. • Shows which level has the most energy and the highest number of organisms. Ecological Pyramid Ecological Pyramid