Populations and Ecosystems

Populat= ions and Ecosystems

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An ecosystem is an organizational unit of life on Earth, defined by a physical environment a= nd the organisms that live there.

Organisms depend = on their ecosystem for survival. Disruption to one element of the ecosystem produces waves and ripples that touch every member of the system. The ripple’s impact on an individual organism depends on the relationsh= ip between the organism and the change as well as the traits expressed by the individual. Changes may produce pressures in the ecosystem.

When changes in ecosystems are incremental, genetic flexibility may allow a population to change over time to adjust to the new conditions. When change is precipit= ous, a population may be exterminated.

One powerful chan= ge agent in just about every ecosystem on Earth is humans. Human mobility, technology, and institutions place pressures on many ecosystems. The first step toward placing less disruptive pressure on natural systems is understanding how they work and what they need to remain healthy.

This course provi= des students with the first steps along the path of ecological understanding, with the hope that their future steps will be considered and measured, serving the interests of all life.

Investigations:

1. In Milkweed Bugs students explore reproductive biology and population dynamics.
2. Sor= ting out Life introduces students to ecology.
3. In <= b>Miniecosystems students investigate ecosystem interactions.
4. In Mono Lake stude= nts investigate food webs.
5. In Finding the Energy<= /b> students learn that food energy is derived from the Sun, which drives life processes= .
6. In Population Size students explore factors that limit population size.
7. In <= b>Ecoscenarios students research and analyze ecosystems.
8. Adaptations introduces students to the concepts of adaptation and variation.
9. In Genetic Variation students learn genetic mechanisms to determine traits of individulas in a population.
10. Natural Selection introduces students to environmental pressures= .

Context:

What comes before:

This FOSS kit serves as the primary instructional material for the second semester of the 6^th grade science course, beginning in January. Another important life science kit, FOSS Diversity of Life, makes = up the majority of the first semester of 6^th grade. A unit on light, sound and waves is completed following Populations and Ecosystems.

Students raise Milkweed Bugs in second grade in the FOSS Insects unit, so many 6^th graders will have put tog= ether a Milkweed Bug habitat. In addition, students learn concepts that provide foundation for this unit in = the 5^th grade FOSS Environments unit. This includes understanding that:

·            = ;         everything = that surrounds an organism makes up its environment.

·            = ;         organisms h= ave ranges of tolerance for environmental factors.

What comes after:

The next course in which students study ecology is high school Biology. This unit provides underpinnings for genetics and evolution.

Content: Four major c= ontent strands

1.&n= bsp;     Develop students' understanding of populations and ecosystems.

A population consists of all individuals of a species that occur together at a given place and tim= e. All populations living together and the physical factors with which t= hey interact compose an ecosystem.

Populations of organisms can be categorized by the function they serve in an ecosystem. Plants and so= me microorganisms are producers—they make their own food. All anim= als, including humans, are consumers, which obtain food by eating other organisms. Decomposers, primarily bacteria and fungi, are consumers t= hat use waste materials and dead organisms for food. Food webs identify t= he relationships among producers, consumers, and decomposers in an ecosystem.

For ecosystems, the major source= of energy is sunlight. Producers use photosynthesis to transform energy entering ecosystems as sunlight into chemical energy. That energy then passes from organism to organism in food webs.

The number of organisms an ecosy= stem can support depends on the resources available and abiotic factors, such as quantity of light and water, range of temperatures, = and soil composition. Given adequate biotic and abio= tic resources and no disease or predators, populations (including humans) increase at rapid rates. Lack of resources and other factors, such as predation and climate, limit the growth of populations in specific ni= ches in the ecosystems.

2.&n= bsp;     Develop students' understanding of reproduction and heredity.

Reproduction is a characteristic= of all systems; because no individual organism lives forever, reproducti= on is essential to the continuation of every species. Some organisms reproduce asexually. Other organisms reproduce sexually.

Every organism needs a set of instructions for specifying its traits. Heredity is the passage of th= ese instructions from one generation to another.

Hereditary information is contai= ned in genes, located in the chromosomes of each cell. Each gene carries a single unit of information. An inherited trait of an individual can be determined by one or by many genes, and a single gene can influence m= ore than one trait.

The characteristics of an organi= sm can be described in terms of a combination of traits. Some traits are inherited, and others result from interactions with the environment.<= o:p>

3.&n= bsp;     Develop students' understanding of diversity and adaptations of organisms.

Biological evolution accounts fo= r the diversity of species developed through gradual processes over many generations. Species acquire many of their unique characteristics thr= ough biological adaptation, which involves the selection of naturally occurring variation in populations. Biological adaptations include changes in structures, behaviors, and physiology that enhance survival and reproductive success in a particular environment.

4, Develop students' understanding of changes in environments.

·         E= nvironments are the space, conditions, and factors that affect an individual's and a population's ability to survive and quality of life.

·         Changes in environments can be natural or influenced by humans. Some changes are go= od, some are bad, and some are neither good nor bad.