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Investigation 1 – Concept Day








Ecosystems: Investigation 1

Concept Day


Note: In this first Investigation of the Ecosystems CELL, we wish to establish several basic concepts. First, we will briefly discuss the organization of life on Earth – that molecules make up cell structures and that cells organize to form tissues, and so on. Eventually, such an organization builds to entire populations of plants and animals that interact with the physical components of the world around them in complex ecosystems.

We will then discuss food chains and the flow of energy through the various trophic levels of an ecosystem. Finally, we will introduce a model for simulating energy flow through an ecosystem that you will use in Investigation 1 lab.



  • This slide is a good review of much of what you have probably learned previously from CELLs like Atomic Structure, Cellular Structure, Adaptation, and Photosynthesis.

Note: Sometimes students don’t consider a bone to be an “organ” or the skeleton to be an organ system. However, they are. Other examples that could have been used to represent an organ system used include the nervous system, the circulatory system, the respiratory system, and so on.

  • The new information in this slide begins at the “population” level. Individual organisms never exist entirely alone. Without breeding populations, a species would not reproduce and therefore would become extinct in a generation. Even if individuals lead relatively solitary lives, they must gather periodically in order to reproduce the next generation. The individuals that do so within a given geographic range are called a population.
  • The important term ecosystem includes populations of plants, animals, and the physical environment in which they exist. The study of ecosystems involves not only an account of the variety of different plants and animals within them but also the interactions between plants and animals and between plants and animals and their environment. What are the sizes of the populations? What animals consume what types of plants? What animals consume other types of animals? How many plants and animals can a given area of an ecosystem support? How does energy from the Sun flow through the ecosystem? These are the questions of the science of Ecology.
  • Given the sheer size and diversity of its components, it turns out the study of ecosystems, the science of Ecology, is truly awesome in its scope. Other sciences, in addition to biology, including physics and chemistry, are constantly used to understand the complexity and underlying logic of ecosystems.

Note: It is therefore somewhat fitting that we have placed this CELL near the end of the LabLearner middle school curriculum. You will need to draw upon much of what has come before to truly understand ecosystems.



  • This slide simply focuses the discussion on the population level of the previous slide.
  • It is important to realize that many, many populations of both plants and animals exist in an ecosystem. Some of these populations, like the moose pictured in this slide, are fairly obvious. However, a population of fir trees of a particular species may be interspaced with trees and plants of a thousand different species and be less obvious populations of a given ecosystem.
  • Beneath the soil, countless populations of different species of microorganisms help decompose dead material that enters the soil (detritus) from above. There are populations of insects, amphibians, ferns, moss, reptiles, and so on in an ecosystem.
  • Some populations of animals may only be components of a particular ecosystem temporarily. Many species of birds, for example, come and go as they exercise their annual migrations, sometimes spending one part of the year in one ecosystem, perhaps summer in northern pine forests, and another part of the year in another, perhaps a more tropical system much further south, ecosystem.



Note: This slide focuses the discussion on the ecosystem level. It should accentuate that an ecosystem not only encompasses the many plant and animal populations in a given geographic area but also the physical components of the environment as well.

  • Physical components of the environment are many. Rainfall, amount of sunlight, temperature, soil type, salinity of water supplies, etc., all greatly impact the plants and animals of any ecosystem.
  • We often assign names to individual ecosystems. However, each and every square centimeter of the Earth’s surface is in one ecosystem or another. Commonly referred to ecosystems include, in addition to the dessert, pine forest and coral reef systems listed on this slide:
    • Grasslands, Open Ocean, Fresh Water Lake, River, Rainforest, Savanna, Cave, Tropical Salt Pond, Human Urban, and many more.



  • Finally, we come to the biosphere. The biosphere is the sum total of all ecosystems on Earth.
  • The biosphere consists of all of the individual ecosystems in its three major components, the lithosphere, hydrosphere, and atmosphere. The lithosphere is the solid, rocky land that exists on Earth. The hydrosphere describes the sum total of all aquatic environments on the planet. The Earth’s surface is about 71% covered with water. Most of the volume of water on Earth is in the form of ocean saltwater, more than 96%. The atmosphere completely encircles the Earth. It consists of gases and extends out to about 100 km, where outer space begins.



  • In preparation for a discussion of the food web, this slide introduces some important major divisions of plants and animals.
  • Organisms on Earth can be autotrophs or heterotrophs. The suffix –”troph” from Greek, means nutrition or nutrients. Thus, autotrophs can make their own food. These are essentially the plants and some microbes that can photosynthesize. This is why plants are called producers – they produce their own food and nutrients directly from the Sun.
  • Heterotrophs, on the other hand, cannot photosynthesize and therefore must obtain their nutrients for life from either plants or other animals. This is why we refer to heterotrophs as consumers – they consume other organisms to survive.
  • Heterotrophs can be further divided into herbivores, carnivores, and omnivores. Herbivores eat only plant material – they consume no animal tissue. Carnivores eat only meat. Finally, omnivores eat both plant and animal tissue to obtain their nutrients. Humans are omnivores.



  • This highly simplified slide introduces the concept of a food chain. It is simple because it suggests that one type of insect eats plants and is eaten by only one type of rodent. The snake is shown to only eat rodents and the bird of prey eats only snakes. In the real world, each of these levels may feed on a variety of other organisms and, in turn, may be preyed upon by many different organisms. Thus, a simple food chain as shown here, quickly expands into a food web, with many predatory relationships described.
  • Notice that this slide includes several Trophic Levels. Each of the steps on this slide represents a different trophic level. The plant, insect, mouse, snake, and bird are each at a different trophic level. Obviously, there can be many different organisms at the same trophic level. There are thousands of different species of plants for example, yet all plants are at the producer trophic level. In this slide, only the beetle is shown to feed directly on plants, whereas, many other species in a real ecosystem will likely feed on plants as well. Rabbits, other insects, elephants all feed directly on plants.
  • A final point shown on this slide is at the lower left, the decomposers (detritivores). These are heterotrophs (they can’t make their own food like autotrophs) that breakdown or decompose dead plant and animal tissue to obtain their nutrients to survive and reproduce. This is a very important component in the food chain as decomposers return many nutrients to the ecosystem for future plant and animal growth and reproduction.



  • This slide presents the food web relationship from the preceding slide in another format. A pyramid is represented with producers at the bottom of the pyramid. Above the producers, beetles are pictured. Animals like this, those that feed directly on plant material and are herbivores, are referred to as primary consumers.
  • As we move up the pyramid, we encounter secondary, tertiary, and quaternary consumers (or Apex Predators). There may be more trophic levels than this, depending on the ecosystem under study.
  • Beneath the pyramid are the decomposers. They are not fit into the pyramid because they are generally not fed upon. They are sometimes simply left off pyramid representations all together.
  • Finally, notice that at each trophic level there are fewer and fewer organisms and “biomass”. Biomass is a measurement of the dry weight of organisms. This decreasing number of individuals and their associated biomass is what gives the pyramid its shape in such models.



  • This final slide simply depicts the model of energy flow through trophic levels that we will address in Investigation 1 lab. In the lab, a dye will be added to water to represent the amount of energy reaching an ecosystem from the Sun. As this energy moves through the trophic levels of a system, it becomes more and more dilute.
  • The amount of dye in each sample will be determined by measuring absorbance/transmittance using the spectrophotometer.

Note: You should be familiar with the operation of the spectrophotometer. If not, consult your Procedural Toolbox for clear instructions. Remember to blank the instrument before reading the sample.