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Biology LibreTexts

2.2: Introduction

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  • Read the following sections before lab.

    This lab manual begins by looking at the microscopic, working its way up the hierarchical organization of organisms through cells, tissues, organs, and organisms, until it arrives at large-scale evolutionary groups. For many, this series of content will only make sense if it is first situated into a larger context. This can be accomplished in a variety of ways -- perhaps a field trip looking at interacting pieces of an ecosystem, designing and building a terrarium, or a survey of samples from the different organismal groups covered in botany. How you experience this introduction will be dependent upon the resources (and weather) available to you! The content in this first lab is designed to supplement multiple methods of approach by explaining the foundational principles of ecology and allowing you the flexibility to apply them to any context.


    An ecosystem includes both the biotic (living) and abiotic (nonliving) components in a given environment. Though every ecosystem will be composed of a unique assemblage of interacting factors, we can classify the organisms in them by the roles that they fulfill. For example, all ecosystems require a primary producer. A primary producer is an organism that uses some external, abiotic energy source (e.g. electromagnetic or chemical energy) to build organic molecules.

    In many ecosystems, plants act as the primary producers, using energy from sunlight to build sugars from the carbon atoms in carbon dioxide through a process called photosynthesis (photo- meaning light, synthesis- meaning to form or put together). However, we often overlook the other organisms who share this role, algae and photosynthetic bacteria.

    Energy Flow Through Ecosystems

    Collectively, we can refer to plants, algae, photosynthetic bacteria, and chemosynthetic bacteria as autotrophs (auto- meaning self, troph- meaning feeding), because they all use an abiotic energy source to form organic molecules: they make their own food. Organisms who cannot make their own food must consume other organisms to survive, obtaining energy by breaking down the complex molecules built within those other organisms. These are referred to interchangeably as heterotrophs (hetero- meaning other) and consumers.

    In any given ecosystem, there may be a hierarchy of who eats whom. Primary consumers eat primary producers and can also be called herbivores. Secondary consumers eat primary consumers, while tertiary consumers eat secondary consumers. Rarely is ecology quite so clear cut, and any of these levels might also consume “lower” levels of the food chain, which is why it might be more accurate to refer to this transfer of energy as a food web.

    There is another important category of organisms that aids in the completion of this network--the decomposers. Decomposers break down dead organic matter, transforming the molecules that made up those organisms into forms that are released into the environment and reabsorbed by primary producers. These organisms have a multitude of names that they may be referred to as, including detritivores, saprotrophs, saprophytes, and saprobes (sapro- meaning death or decay). Some important decomposers studied under the umbrella of botany are the true fungi, Oomycota (water molds), and the Myxogastria (slime molds).


    This is the end of the material that you should have completed reading prior to lab. In future labs, this won’t be explicitly stated, it will be your responsibility to keep up with the pre-lab information.

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