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Content Benchmark L.12.C.1
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Life Science
Structure of Life
Organisms and Their Environment
Diversity of Life
Content Areas
Nature of Science (NOS)
Life Science
Earth Science
Physical Science

Students know relationships of organisms and their physical environment. E/S

Ecology is the study of the interaction between organisms and their environment. Biotic factors are the living components of an ecosystem including interactions between organisms. Abiotic factors are the nonliving components that affect the living including water, oxygen, light, temperature, soil, and nutrient cycles. The abiotic factors collectively dictate where ecosystems exist.

Figure 1. Locations of world biomes.

Abiotic Factors
Light: The energy that drives life on earth originates from the sun. The amount of sunlight dictates the growth of plants. Therefore, energy directly relates to where biomes are located. Both the intensity and duration of light varies with latitude. Radiant energy is greatest at the equator and decreases as you travel to the poles. Areas near the equator receive approximately 12 hours of daylight everyday. Areas near the poles receive 24 hours of weak intensity light in “summer” and 24 hours of darkness in “winter”. Figure 2 shows how one unit of energy from the sun at the equator covers a smaller area than the same unit of energy at the poles creating the weaker intensity of light at the poles. Day length varies with the seasons, lengthening as you approach the summer solstice and shortening as you move toward the winter solstice.

Figure 2. A unit of energy from the sun at the equator covers a smaller unit of area than the same unit of energy at the poles. From:

Sunlight is also affected by depth of water. As light penetrates water, certain wavelengths are absorbed. The zone which is penetrated is called the photic zone and below that is the aphotic zone. Most of earth’s photosynthesis takes place in the photic zones of the oceans and the organisms that live in the aphotic zone are heterotrophic and feed off on the photic zone organisms that migrate to deeper depths.

Figure 3. Red and yellow light are absorbed in the first 15 meters while blue light can penetrate 37.5 meters.

Figure 4. Red and yellow light are absorbed in the first 15 meters while blue light can penetrate 37.5 meters.


Temperature: Temperature patterns are affected by both latitude and altitude. There is a direct relationship between the decreasing light energy received (as latitude increases) and the decrease in temperature. The hottest regions of earth are equatorial and the coldest regions are polar. As you travel away from the equator, these zones have decreasing average annual temperatures. Conversely, there is an inverse relationship between altitude and temperature. As altitude increases, average temperature decreases within the troposphere. As a result even the tops of equatorial mountains may have snow.

Water: Water is essential to life and is recycled through the water cycle (See Benchmark L.12.C.3). The amount of precipitation (including rain, snow, hail, and sleet) that an area receives dictates the type of vegetation. Precipitation is affected by latitude, altitude, topographic features, and proximity to large bodies of water.

Figure 5. Why are deserts at 300 degrees N/S of equator?

The equatorial regions tend to be very wet while many deserts are located around 30 degrees north and south latitudes. Air over the equator is disproportionately heated because of the increased solar energy. This results in air masses that expand creating low pressure systems. As the air mass rises, it cools, and it loses its moisture. These air masses then move away from the poles, cool, condense, and sink creating a high pressure system. The increased air pressure and dryness causes the air mass to draw water out of the environment creating deserts.

Soil and Minerals: Soil is another non-living component important to the health of an ecosystem. Soil is defined as the unconsolidated mineral or organic material on the immediate surface of the earth that serves as a natural medium for the growth of land plants ( There are many types of soils and each one has unique characteristics, like color, texture, structure, and mineral content. The type of soil dictates the type of vegetation.

Figure 6: Soil profiles from various ecosystems. Notice how the differences in soils correlates to the type of vegetation supported.

The process of soil formation in an ecological sense is called primary succession (see Benchmark L.12.C.2). In general, as soil forms, three distinct layers can be distinguished. The uppermost layer is the topsoil or A Horizon. This includes organic matter and various living organisms. It is often dark in color from the high organic content (humus) which is from the decay of dead plant and animal matter. The middle layer, or B Horizon is called the subsoil and consists of partially weathered rock particles and an accumulation of water soluble minerals leached from the topsoil. The bottom layer or C Horizon, consists of partially weathered parent rock with little organic matter.

Figure 7. A generic soil labeled profile

Climatograms: A climatogram is a graphical way to highlight the differences between biomes. The graph shows a biome’s average monthly temperature and average monthly precipitation data on a single graph. The precipitation is presented as a bar graph using the left axis and the temperature data is plotted as a line graph using the right axis.

Figure 8: Two examples of climatograms. The data from Indonesia represents a tropical rainforest. The data from Arizona represents a desert. Indonesia:

Biotic Factors
Ecological Hierarchy: Organisms in an ecosystem do not live in isolation. They interact with their environment and with other organisms. Therefore, an understanding of the organization of an ecosystem is necessary in the field of ecology. The hierarchy starts with the individual. The simplest grouping of organisms is a population. A population is defined as a group of organisms of the same species that have the potential to interact and interbreed with each other. For example, all of the mountain lions that live in the southern Sierra Nevada Mountains would be a population and the mountain lions in northern Nevada would be a separate population. A community consists of all the populations of different organisms in a given location. The community level of study looks at the inter-specific relationships, like predator prey relationships or competition. Food webs are another way to think about an ecological community. Food webs are covered in detail in Benchmark L.12.C.3. Lastly, the zone on Earth where life can exist is the Biosphere. The Biosphere is about 20km thick extending from the floor of the ocean and reaching up to the limits of life in the atmosphere. An extended definition form defines the biosphere as the outermost part of the planet's shell — including air, land, surface rocks and water — within which life occurs, and which biotic processes in turn alter or transform.

Figure 9: An example of an ecological hierarchy from population to ecosystem.

Ecological relationships: Again, organisms do not live in isolation. They must interact with their environments and other organisms. Ecological relationships are relationships in which two different organisms interact regularly to the benefit of at least one of them. There are three basic types of ecological relationships: mutualism, commensalisms, and parasitism. The following table illustrates each type of relationship. A + sign represents a benefit, a 0 represents no effect, and a – sign represents a harmful effect.

  Organism #1 Organism #2
Mutualism + +
Commensalism + 0
Parasitism + -

An example of a mutualistic relationship is between termites and the bacteria that live in their digestive tract. Termites cannot digest cellulose and depend on the bacteria to release the nutrients in the wood while the termites give the bacteria nutrition and a place to live.

Barnacles have a commensalistic relationship with whales. The whales are not bothered by the barnacles but the barnacles rely in the water currents created by the whale’s swimming to filter feed.

Tapeworms are parasitic and live inside the digestive tract of a host organism. The worm steals nutrients from the host to grow and reproduce. Consequently, the host loses nutrients, energy, and can suffer from tissue damage from the infestation.

Competition: Resources are limited in an ecosystem. Therefore, individuals must compete with individuals of their own species (intraspecific competition) and with other species (interspecific competition) to meet their survival needs.

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Content Benchmark L.12.C.1

Students know relationships of organisms and their physical environment. E/S

Common misconceptions associated with this benchmark:

1. Species live independently of each other and there environment.
Organisms are constantly interacting with their environments abiotic factors, such as, water, light, soil, and air. Plants, for example, take the radiant energy from the sunlight, carbon dioxide and water to make their food through the process of photosynthesis. These are all abiotic factors. Animals must obtain their energy from other organisms like plants and other animals. These interactions are very specific and are important for stability in an ecosystem.

2. Symbiosis is limited to parasitism, where the parasite goal is to kill its host.
There are three types of symbiotic relationship, parasitism, commensalism, and mutualism. In a parasitic symbiotic relationship one organism benefits by getting food, shelter, and or protection at the expense of a second organism, it’s host. The parasite’s intention is not to kill the host because without the host the parasite will die as well. In a commensal symbiotic relationship, one organism is helped but the other is unaffected. In a mutualistic symbiotic relationship both organisms benefit from the relationship.

3. Biotic factors, like plants and animals, determine the biome.
Biomes are characterized by the predominant vegetation, but the two major determining factors of biomes are temperature and precipitation. Organisms must be adapted to live in the climate that is determined by temperature and precipitation. Many organism adaptations are driven by abiotic factors, for examples, some cactuses have spines that help to reduce water loss and to help shade from excessive sun. This adaptation is ideal for living in high temperatures with low precipitation.

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Content Benchmark L.12.C.1

Students know relationships of organisms and their physical environment. E/S

Sample Test Questions

1st Item Specification: Identify the energy relationships in an ecosystem.

Depth of Knowledge Level 1

  1. Use the desert food web below to answer the following question.

Which of the following organisms have the greatest amount of stored energy
in the food web?

  1. Hawk and Coyote
  2. Grass and Cactus
  3. Roadrunner and Rabbit
  4. Grasshopper and Scorpion
  1. Use the food chain below to answer the question that follows.

What do the arrows in the diagram above indicate?

  1. Flow of energy
  2. Who consumes whom
  3. A common food chain
  4. Trophic levels

Depth of Knowledge Level 2

  1. An energy pyramid is represented below.

Which of the following number sequence represents the flow of available energy from the base of the pyramid to the top of the pyramid in the ecosystem represented above?

  1. 100–100–100–100
  2. 100–75–50–25
  3. 100–50–25–0
  4. 100–20–5–1
  1. Which one of the following does NOT explain why there is a decrease in energy through the trophic levels in an ecosystem?
    1. There is an increase in biomass as trophic levels decrease.
    2. Energy is lost as organisms grow older over time.
    3. There is an increase in the number of individuals as trophic levels decrease.
    4. Energy is lost from the processes of respiration and metabolism.

2nd Item Specification: Classify an organism by the manner in which it obtains energy.

Depth of Knowledge Level 1

  1. Use the desert food web below to answer the following question.

Two of the primary consumers in the food web are the

  1. coyote, rattlesnake, and hawk.
  2. grass and cactus.
  3. rabbit and grasshopper.
  4. rabbit, grasshopper, and scorpion.
  1. Use the desert food web below to answer the following question.

Two of the secondary consumers in the desert environment are

  1. coyote and rattlesnake
  2. grass and cactus.
  3. rabbit and grasshopper.
  4. hawk and coyote.

Depth of Knowledge Level 2

  1. Use the description below to answer the following question.
    In a marine ecosystem, a disease killed most of the sea otters. As a result, the sea urchins and clams increased in number which in turn caused the sea gull population to increase and the seaweed population to decrease.
    Identify a secondary consumer in this marine ecosystem.
    1. Seaweed
    2. Clam
    3. Sea urchin
    4. Sea gull
  1. During a visit to a desert ecosystem, a student observes the following:
  • A hawk eats a snake.
  • A lizard eats a fly.
  • A tortoise eats small patches of grass.
  • A snake eats a mouse.
  • Based on student’s observations of how each of these organisms obtains energy, which of the following statements is the best conclusion?

    1. The hawk is a primary consumer.
    2. The grass and the desert tortoise are both primary consumers.
    3. The lizard is a tertiary consumer.
    4. The lizard and the snake are secondary consumers.

    3rd Item Specification: Describe how an organism’s needs are met by aspects of its physical environment.

    Depth of Knowledge Level 1

    1. Which statement illustrates a biotic factor interacting with an abiotic factor?
      1. A sea turtle transporting a pilot fish to a source of food.
      2. A rock moving during an earthquake.
      3. A plant absorbs sunlight, which is used for photosynthesis.
      4. Wind cause waves to form on a lake.
    1. Identify an organism’s need that is met by an abiotic factor.
      1. A wolf’s need for warmth; fur coat
      2. A fish’s need for food; water
      3. A lizard’s need for warmth; sun
      4. A rabbit’s need for food; grass

    Depth of Knowledge Level 2

    1. A student observes a bear over a year. In the spring the bear comes out of its cave and eats continuously throughout the spring, summer, and fall building up energy reserves for the long winter hibernation. As winter approaches the bear settles down in its cave for the long winter sleep. Which of the following statements is a conclusion specific to how an abiotic factor met the needs of an organism?
      1. The cave provided shelter for the bear throughout the winter.
      2. The bear had food throughout the spring, summer and fall.
      3. Throughout the winter months the bear hibernated.
      4. In the winter, the bear obtains energy from stored fat.
    1. A student observes a rocky coastal ecosystem over a period of a month. As the water begins to go out due to the tides, the animals change behaviors. The clams and mussels close up to prevent water loss and drying out, the crabs move under rocks or into small pools of water in the rocks for shelter, sea birds walk along the rocks eating small organisms, and a raccoon comes down to the shore to eat the exposed mussels and clams. Which of the following statements is a conclusion specific to how an abiotic factor met the needs of an organism?
      1. The clams and mussels closing up to prevent losing water.
      2. The raccoon eating the clams and mussels.
      3. The sea birds eating organisms off the rocks.
      4. The crab finding shelter under rocks or in pools of water.

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    Content Benchmark L.12.C.1

    Students know relationships of organisms and their physical environment. E/S

    Answers to Sample Test Questions

    1. B, DOK Level 1
    2. A, DOK Level 1
    3. D, DOK Level 2
    4. B, DOK Level 2
    5. C, DOK Level 1
    6. A, DOK Level 1
    7. D, DOK Level 2
    8. D, DOK Level 2
    9. C, DOK Level 1
    10. C, DOK Level 1
    11. A, DOK Level 2
    12. D, DOK Level 2

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    Content Benchmark L.12.C.1

    Students know relationships of organisms and their physical environment. E/S

    Intervention Strategies and Resources

    The following is a list of intervention strategies and resources that will facilitate student understanding of this benchmark.

    1. Current Marine Ecology projects with real life data that students can access.
    This is a great website that examines the historical as well as current abiotic data of Racerock Ecological Preserve, Southern Vancouver Island, BC. There are several current marine ecological projects under way so students can observe ecological research in action.

    To access this site, visit:

    2. Biomes of the world, including biotic and Abiotic factors.
    This website presents a very easy to navigate and easy to read about the biomes of the world. It includes land, fresh water, and marine biomes. The information includes both abiotic and biotic description of each biome.

    To access this site, visit:

    3. Soil property Webquest
    This website is a fairly involved webquest that allows students to investigate the properties of soil. It can be easily adapted to fit the needs of any classroom teacher.

    To access this site, visit:

    4. Soil webquest more appropriate for ELL students
    This webquest is very simple but may be appropriate for low level students or second language students as an introduction to soils.

    To access this site, visit:

    5. Printable climatograms
    This is a printable climatogram activity to give students practice graphing and interpreting climatic data.

    To access this site, visit:

    Other American Field Guide activities can be found at

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