Section 4.2 Energy Flow in Ecosystems

I Can…

• LS 2.4 I can analyze data explaining the flow of energy between trophic levels.

• LS 2.4 I can analyze data demonstrating decrease in biomass in each successive trophic level using the laws of conservation of energy and matter.

• LS 2.4 I can construct a mathematical model to describe the transfer of energy and matter between trophic levels and explain the laws of conservation of energy and matter.

Key Questions

1. How does energy flow through ecosystems?

2. How do ecological pyramids help analyze energy flow through trophic levels?

Vocabulary

• Food chain

• Phytoplankton

• Food web

• Trophic level

• Ecological pyramid

• Biomass

Vocabulary from Section 4.1

• Autotroph (producer)- organism that is able to capture energy from sunlight or chemicals and use it to produce its own food

• Primary producer- first producer of energy-rich compounds that are later used by other organisms

Vocabulary from Section 4.1

• Photosynthesis- process used by plants and other autotrophs to capture light energy and use it to power chemical reactions that convert carbon dioxide and water into oxygen and energy-rich carbohydrates

Vocabulary from Section 4.1

• Chemosynthesis- process in which chemical energy is used to produce carbohydrates

Vocabulary from Section 4.1

• Heterotroph (consumer)- organism that obtains food by consuming other living things

Carnivore Herbivore Omnivore

Vocabulary from Section 4.1

• Detritus- small pieces of dead and decaying plant and animal remains

Detritivore Decomposer Scavenger

Food Chains

• Energy flows through an ecosystem in a one-way stream, from primary producers through various consumers.

• Food chain- a series of organisms in which energy is transferred from one organism to another

grass antelope lion

• Phytoplankton- photosynthetic algae found near the surface of the open ocean (a primary producer example)

Food Webs

• Food web- network of feeding interactions, through which both energy and matter move.

Food Chains and Food Webs

A food web is a network that includes all the food chains in an ecosystem.

Decomposers and Detritivores in Food Webs

• Most producers die without being eaten.

• Decomposers convert dead material to detritus, which is eaten by detritivores.

• Decomposition also releases matter in the form of nutrients that can be used by primary producers.

• Without decomposers, nutrients would remain locked within dead organisms.

Food Webs and Disturbance

• What if an oil spill caused a serious decline in the number of bacteria and fungi that break down detritus?

• What effect could that have on populations of shrimp and crayfish?

• If they declined, how might the pig frogs change their feeding behavior?

• How might changes in frog behavior affect other species?

Ecological Pyramids

• Trophic level- each step in a food chain or food web

• 1st trophic level = primary producer

• Ecological pyramids- models that show the relative amount of energy or matter contained within each trophic level in a food chain or food web

• Pyramids of Energy

• Pyramids of Biomass

• Pyramids of Numbers

Pyramid of Energy

• Only a small portion (10%) of the energy that enters any trophic level is available to organisms at the next trophic level.

• Organisms expend much of the energy they acquire on life processes—respiration, movement, growth, and reproduction.

• Most of the remaining energy is released as heat—a byproduct of these activities.

• Pyramids of energy show the relative amount of energy available at each trophic level of a food chain or food web.

Pyramid of Biomass

• Biomass- the total amount of living tissue within a given trophic level

• Measured in grams of organic matter/unit area

• A pyramid of biomass is a model that illustrates the relative amount of living organic matter in each trophic level of an ecosystem.

Pyramid of Numbers

• A pyramid of numbers is a model that shows the relative number of individual organisms at each trophic level in an ecosystem.

• Measured in number of organisms/unit area

Section 4.2 Exit Ticket

1. What is the conservation of mass? What is the conservation of energy?

2. How do matter and energy transfer from one trophic level to another?

3. If matter and energy are conserved, why does the biomass decrease by approximately 90% as you move from trophic level to trophic level?

The End