FOOD WEBS AND CHAINS 7 th Grade Science

OBJECTIVES • Define and give examples of organisms at different trophic levels • Describe how energy flows in a food chain. • Explain why producers must outnumber consumers in a balanced ecosystem.

PRODUCERS • Food chains begin with producers • organism that makes its own food • Green Plants use energy from the Sun to create food through photosynthesis • Make up Trophic Level in an ecosystem • Examples: Grass, Trees, and Algae

CONSUMERS • Organism that get their energy by eating other organisms • “YOU” cannot make your own food, no matter how hard you try! • Must obtain energy from other sources to live and grow (EAT!!!!!) • All animals, including humans are consumers

PRIMARY CONSUMER • First consumer in Food Chain • Obtain energy directly from “Producers” • a. k. a—”HERBIVORES” or plant eaters • Land Ecosystem Herbivores include: • Cows, Deer, and Grasshoppers • Aquatic Ecosystem Herbivores include: • Shrimp, Minnows, and Snails

LAND ECOSYSTEM HERBIVORES

AQUATIC HERBIVORES

SECONDARY CONSUMERS • Eat Primary Consumers • Include “Carnivores” (meat eaters) • Lions, Tigers, Coyotes, and Wolves

TERTIARY CONSUMER • Eats “Secondary Consumer” • Includes: Carnivores and Omnivores • Carnivores: • Only eat meat • Omnivores • Eats both meat and plants • Examples of Omnivores: • Humans and Bears

DECOMPOSERS • Last link in a food chain • Break down nutrients in dead organisms and return essential chemicals to earth: • Nitrogen (N), Carbon (C), and Phosphorous (P) • In land ecosystems, chemicals are released into soil. • In aquatic ecosystems, chemicals are dissolved in water. • Essential part of an ecosystem because: • Producers absorb nutrients to make food • Most common Decomposers are: • Bacteria and Fungi

ENERGY FLOW • Where do you get energy to read, come to school, hunt, and play ball? • Eating what? Food!! • All energy as you already know, comes from the Sun • Producers absorbs the energy and uses “Photosynthesis” to make food • 50% of energy absorbed from Sun is used to live and grow • Unfortunately not all energy is transferred to consumer, due to heat “loss” • Only around 10% of energy is transferred from producer to consumer

BALANCED ECOSYSTEM • Producers outnumber consumers greatly • More Specifically: • Producers outnumber Primary Consumers • Primary Consumers outnumber Secondary Consumers • Secondary Consumers outnumber Tertiary Consumers and so on……. • Since energy decreases 10% with each Trophic level, it is very important for higher level consumers to eat a lot to get enough energy to survive. • Example: • Even though a mouse only has to eat a few stalks of grass to have energy, a snake must eat several mice to survive. To take this one step further, a hawk has to eat even more snakes!

TROPHIC PYRAMID

FOOD WEBS • Used to represent the complex food relationships between organisms in an ecosystem. • Network of interconnecting food chains

FOOD WEB #2

END OF CLASS REVIEW • How much energy is transferred from one trophic level to the next? • Describe a Balanced Ecosystem. • Where do producers get their food and how? • What are the 3 types of consumers? How do they get their food? • Describe a food web