Chapter 13: Energy and Nutrients Section 13-2: Energy Flow in the Biosphere

Energy Begins at the Sun Energy begins at the sun!!!! Green plants harness the sun’s energy through photosynthesis Plants are primary producers (autotrophs) because they use the sun’s energy to change simple, nonliving chemical nutrients (water and carbon dioxide) into living tissues

Consumers Animals are consumers (heterotrophs) because they cannot make their own living tissues – must consume other organisms to obtain energy and nutrients Can be: – Herbivores – eat autotrophs – Carnivores – eat other animals – Omnivores – eat plants and animals

Consumers Parasites are technically heterotrophs because they live on other organisms and get nutrition from their hosts, though they do not necessarily kill their hosts right away Decomposers (mainly bacteria, fungi) are technically heterotrophs because they feed on the dead bodies of animals and decaying plants or their waste products

Energy Flow Through the Biosphere Energy cannot be recycled – there is a one-way flow! SUNLIGHT ↓ PRIMARY PRODUCERS ↓ CONSUMERS ↓ DECOMPOSERS

Trophic Levels Each step in the series of one organism eating another makes up a trophic level, or feeding level. The greater the number of trophic levels between consumers and primary producers, the smaller the amount of energy available to the consumers compared to the energy originally captured by the primary producers.

Trophic Levels Only 10% of the energy at one trophic level can be used by the consumers at the next trophic level. Most of the energy is used by the organism at that level.

Ecological Pyramids An ecological pyramid shows how energy is transferred from primary producers to herbivores to carnivores. The less energy available at a trophic level, the less living tissue that level can support

Ecological Pyramids Three types (p. 290, Fig. 13-7) – Pyramid of energy – Pyramid of biomass (living tissue) – Pyramid of numbers