ECOSYSTEMSEnergy Flow and Nutrient Cycling

Watch the following clip: http://saferenvironment.wordpress.com/2008/08/19/explosive-population-growth-affects-world-food-supplies-and-environment/

(up to 1:58)What kinds of problems does the human

race face if the population increases further?

Suggest some possible solutions to the food shortage problems.

Why is it more environmentally friendly to eat more vegetables (think of food chains)?

What are the issues even with producing enough grains and vegetables for all humans?

I. OverviewAll living organisms need energy to fuel their

life processes. Energy can be obtained by photosynthesis or

by taking in food.Energy flows through the ecosystem from

producers to consumers to decomposers. At the end of the food chain the energy cannot be recycled and is lost for living organisms.

Ecosystems, however, do not run out of energy because of the constant influx of energy mostly from the sun.

Chemical compounds are recycled back into the food chain. After decomposers break chemicals down, producers can take them in again and build them into their organic molecules.

II. Energy FlowTo measure how much energy is converted into

organic matter in an ecosystem, we can measure the mass of organic material (living organisms) in an ecosystem. This mass is called biomass.

Primary production – The production of organic matter from CO2 in the atmosphere by mostly photosynthesis in a given area in a certain time period.

Organic material includes proteins, carbohydrates, fats and nucleic acids.

Primary production builds these organic materials into plants, algae and photosynthetic bacteria.

Consumers all get the organic material from the producers (remember the food chains and webs that we learned)

Only about 5-20 % of all energy moves up from one trophic level to the next. The rest of the energy is used up by the organism or lost as heat.

This is the reason why eating more meat puts a lot more strain on the ecosystem than eating vegetables and grains and fruit.

Food label activity

III. Pyramids of EcosystemsThe production of organic matter is

frequently represented by three different graphs:Pyramids of numbers – represent the number

of organisms on each trophic levelPyramids of energy – represents the calories

of energy on each trophic levelPyramids of biomass – represents the mass

of organic matter on each trophic levelAnalyze these pyramids by using the given

handout.

IV. Nutrient CyclingWe are going to discuss and put these cycles

together as a small group activity. We are also going to construct the notes together on the following cycles:

The water cycleThe carbon cycleThe nitrogen cycle