GRADE: Seventh

CONTENT STANDARD: Environmental Science

CONTENT TOPIC: Populations and Ecosystems

CONCEPT: Ecosystems are dependent on interrelationships within the environment.

PERFORMANCE OBJECTIVE: 7G1.00 To understand the relationships of organisms in ecosystems

INSTRUCTIONAL OBJECTIVES: The learner

1.01 be able to construct a model of an ecosystem.
1.02 recognize different trophic levels (feeding levels).
1.03 be able to recreate a food chain for an animal.
1.04 be able to differentiate energy flow and nutrient cycling.

I. Biosphere
II. Model of ecosystem
A. Primary Producers
B. Herbivores
C. Carnivores
D. Omnivores
E. Decomposers
F. Nutrient Reservoir
G. Solar Radiation
H. Respiration
I. Biomass
III. Energy flow and nutrient cycling in an ecosystem
A. Thermodynamics
B. Entropy
IV. Food Web
A. Food chains
B. Niche
C. Trophic level
D. Limiting factors

TN COMPONENT OF SCIENCE: Process of Science

TN GOAL:

To enable students to demonstrate the processes of science by posing questions and investigating phenomena through language, methods and instruments of science.

1.1 OBSERVING - The senses are used to develop an awareness of an event or object and the properties thereof.

1.1a Observing is a process used to develop an awareness of the surrounding environment.

BENCHMARK: By incorporating prior knowledge with the process of observation, a better understanding of one's environment may develop.

TIME REQUIRED:

5 days

Abiotic, biotic, carnivore, consumers, decomposers, ecosystem, Eltonian Pyramid, energy flow, food chain, food web, herbivore, niche, nutrient cycling nutrient reservoir, omnivore, primary producer, respiration, trophic level

There are many different kinds of living things on the earth. Some of these living things are plants, animals, fungi, and microbes. All these living things can be found only in one zone of the earth. This part is known as the biosphere. This is the part of the earth in which life exists. The biosphere is also called the earth's zone of life. It extends from the depths of the oceans to about 11 kilometers above the surface of the earth. All living things are found in this zone. The term ecosystem reflects the total relatedness of nature. There is no line separating biotic and abiotic, water and air. Water, minerals, and energy-supplying materials are in constant circulation. All of these things flow in and out of animal bodies, plant bodies, lakes, and streams.

Solar radiation is the ultimate source of energy for all organisms. Plants utilize sunlight, chlorophyll, water, nutrients, and carbon dioxide to manufacture glucose and release oxygen. We call plants primary producers. Animals consume these plants. We call these consumers. Another name for plant eaters is herbivore. Carnivores eat herbivores. Omnivores eat both herbivores and carnivores. Man is an omnivore.

Energy flow in an ecosystem is one way. It is not cycled; however it is used and dispersed. Respiration goes on at all trophic (feeding) levels. Much energy is lost in the form of heat. The higher the trophic level, the less energy is available to the consumer. Decomposers are an essential part of this model, also. Their primary function is to cycle nutrients. They are responsible for the breaking down of organisms into organic compounds which are added to the nutrient reservoir which contains, among others, the limited nutrient, phosphorus.

Biomass, or living weight, is formed by a process of production. An organism must have energy for this to occur. Primary production is an example. C₆H₁₂0₆ ---> 6C0₂ 6H₂0 + energy. This energy is then used by a consumer and the result is growth.

The first law of thermodynamics states that energy can neither be created nor destroyed. In other words, the amount is constant. Energy can, however, be converted. Ex: light -> chemical bond energy (but not with 100% efficiency). Energy will be lost here in the form of heat. Entropy is defined, ecologically, as randomness. Humans have low entropy. An organism is highly organized and is not randomly distributed. It must use energy to fight entropy. If an organism stops using it, death will occur.

No organism can live to itself. Within a community there is competition for food. Organisms draw from the environment a constant supply of energy which is necessary for keeping them alive. A balanced ecosystem is one in which the flow of energy through the system - or of the food which represents the energy - is steady. The concept of a food web is necessary because many kinds of plants live side by side, and because most animals can eat more than one kind of food. A food web can be described as the food relationship among all organisms that share the same environment.

A food chain is a chain of eating and being eaten that connects large and carnivorous animals to their ultimate plant food. A classical example is: pine trees ----> aphids ----> spiders ----> mice ----> hawk. A food web is a grouping of interrelated food chains. Each piece of this chain is called a trophic (feeding) level. In a food chain, matter differs from energy in that the matter can be recycled. The transfer of food from animal to animal is called the food cycle. The movement of calories is unidirectional (both ways) since energy is degraded in the process. Carbon dioxide is released to the atmosphere by all organisms. Animals high on the food chain are both larger and rarer than animals lower down. This is referred to as the Pyramid of Numbers or Eltonian Pyramid. This model has an order of magnitude of 10.

A niche is the function of an organism in an ecosystem. It relates to what it uses as food and what uses it as food. The niche is the role of an organism in the community. An animal's niche is how it satisfies its need for food and protection. Zebras and lions have the same habitat, the grasslands of Africa. A zebra eats grass and a lion eats meat. Thus, they have different niches. Any organism occupies a given niche. The number of niches in an ecosystem is limited. In a certain area, two populations may try to occupy the same niche. Then they compete with one another. The one that is better adapted for the niche will win and will crowd out the other population. In a stable community, two organisms cannot occupy the same niche. Factors of the non living physical environment that limit where organisms live are called limiting factors. For plants, the limiting factors are the amount of sunlight and moisture, the type of soil, and the temperature. Limiting factors for animals include water, shelter, and proper temperature.

1. (Have the students reproduce a model of an ecosystem complete with labels. This model should show structure and function.

Remind the students that the ultimate source of energy is solar radiation. Consumers take in glucose and release carbon dioxide, water, and energy; however, it respires as the primary producers do. All of these organisms then decompose. Energy is not cycled through an ecosystem. It is used and dispersed. Nutrients, however, are cycled through the system.)

2. (Use a model plan- kit to walk students through the model they have drawn to illustrate how each level is dependent on the other and is necessary for dispersal of energy.)

3. (Have each student choose an animal and trace energy flow from the primary producer up the food chain. They will need to refer to the Eltonian Pyramid here. A model should be available for them. Remind them of the order of magnitude in this pyramid.)

4. (Have the class divide into groups and research the food web of an aquatic animal. This will be the most interesting research project. Aquatic animals are much smaller and the resulting food web can become quite intricate. Beginning with plankton, trace the feeding habits of, for instance, a blue whale.)

We have spent five days discussing the model of an ecosystem and a food web. On a piece of paper, tell me where man can be found in this model and why he is found there.

(Plan a field trip which will involve two-three days. This will allow time for the students to reacquaint themselves with their natural surroundings. Only through an experience like this can they fully appreciate the concept of an ecosystem.)

abiotic - non living

consumers - animals whose source of nourishment is from an outside source

decomposers - bacteria and fungi whose primary function is to cycle nutrients

ecosystem - a community and its total environment

Eltonian Pyramid - a pyramid of numbers developed by C.S. Elton which shows that the higher the level, the fewer the number. The difference in numbers has an order of magnitude of 10.

energy flow - use and dispersal of energy through a .food chain

food chain - a chain of eating and being eaten that connects large and carnivorous animals to their ultimate plant food.

food web - group of interrelated food chains more characteristic of an ecosystem

herbivore - "grazers"

niche - the function of an organism in an ecosystem

nutrient cycling - cycling of nutrients through a food chain

nutrient reservoir - "receptacle" created in the soil by decomposition of organic matter

omnivore - can consume either herbivore or carnivore

primary producer - organism which can carry on photosynthesis

respiration - the conversion of glucose to carbon dioxide, water, and energy

trophic level - feeding level of an organism

This is the time this file has been accessed since 04/02/98.

The University of Tennessee at Martin is not responsible for the information or views expressed here.

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