Trophic LevelsTrophic EfficiencyBioaccumulation

Seatwork Read pages 24-26 and then answer the

following questions. LEAVE SPACE after each answer.

Define trophic level and give several examples.

Define biomass. Define trophic efficiency Define bioaccumulation. Define biomagnification.

A trophic level is a category of organisms that is defined by how the organisms gain their energy.

Examples: First trophic level = primary producers Second trophic level = primary consumers

(herbivores) Third trophic level = secondary consumers

Trophic Levels

Biomass is the total mass of living organisms in a defined group or area.

It includes living cells and tissues that have been assembled by organisms using solar energy.

Plant material is packed with chemical energy that has been converted from solar energy.

Animals indirectly rely on solar energy by eating plants or animals.

Biomass

Trophic efficiency is a measure of the amount of energy or biomass transferred from one trophic level to the next higher trophic level.

Trophic efficiencies are quite inefficient – only about 10%.

Organisms use much of the energy from the biomass they consume for life functions and wastes they produce

Trophic Efficiency

Herbivores don’t eat all of the plant

Not everything that is eaten is digested

Reasons for Biomass Decreases Between Trophic Levels

Energy is lost as heat by organisms Energy is used for life processes

Reasons for Energy Decrease between Trophic Levels:

Because of the inefficiencies of energy transfer among trophic levels, there are usually fewer carnivores than herbivores and fewer herbivores than plants

Relative Numbers at Trophic Levels

Bioaccumulation is a process in which materials, especially toxins, are ingested by an organism at a rate greater than they are eliminated.

Biomagnification is the increase in concentration of a toxin as it moves from one trophic level to the next.

Water Pollution and Bioaccumulation

Read pages 25-27 and then answer the following questions:

1. Explain how the use of DDT and PCB’s are example of bioaccumulation and biomagnification.

2. Review Questions 5 to 8 on page 27

Seatwork