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Education
Energy Dynamics
 

Learning Objectives

At the end of this lab, students should know...

What do we mean by trophic level?

Each interaction in a food chain when energy is transferred from a consumed organism to a consumer organism is called a trophic level.

What are primary producers and consumers?

Primary producers are autotrophic organisms that generate organic materials. Primary consumers, which are organisms that cannot make their organic materials, consume primary producers. However, primary consumers can be sources of energy to others that are secondary consumers.

What is biomass?

Organic material stored in an organism is called the biomass and excludes the water contained by the organism.

What do we mean by productivity and what are different forms of productivity?

Productivity is the rate at which organisms gain biomass from received energy. Productivity of primary producers is called primary productivity and of others is called secondary productivity. They can be further categorized into two forms: gross and net. For instance, gross primary productivity is the rate at which photosynthesis or chemosynthesis occurs, while net primary productivity is the rate at which energy is stored as biomass in these organisms.

Why is it important to study energy dynamics in ecosystems?

Organisms in an ecosystem depend on resources they consume and are connected by the flow of energy and matter from one another. Changes in the balance can have detrimental effects to other organisms in the food chain, including humans. Understanding energy dynamics can help find solutions to mitigate negative effects of changes in the ecosystems, such as keeping populations under control or preventing secondary extinctions.

List of Materials

  • Plastic tubs with lids
    10
  • Petri dishes
    10
  • Weigh dishes/boats
    20
  • Forceps
    20
  • Spray bottle (Distilled water)
    5
  • Spray bottle (70% ethanol)
    5
  • Radish seeds
    5
  • Pieris rapae (eggs)
    Dependent on the lab size
  • Potting mix
    Dependent on the lab size
  • Paper towels
    Dependent on the lab size
  • Weighing scale
    Dependent on the lab size
  • Incubator (set to 37°C)
    Dependent on the lab size

Lab Prep

  1. Cabbage Pre-Weighing
    • To obtain the percent biomass of a representative cabbage before the experiment, use a paper towel to wash and pat dry the inner leaves of a grocery store cabbage.
    • Place the cabbage into a pre-weighed Petri dish on a balance to determine the wet mass of the vegetable, and then transfer the cabbage and the dish into a 37 °C incubator for 48 hours.
    • At the end of the incubation, weigh cabbage in the dish again to obtain the dry mass of the cabbage.
    • Then, calculate the percent biomass of the representative cabbage by dividing the final dry mass of the cabbage by the initial wet mass of the cabbage. After this, multiply the obtained value by 100.
  2. Hatching Pieris rapae Eggs
    • To hatch the Pieris rapae butterfly eggs, one week before the egg acquisition, sow radish seeds in pots containing fresh potting soil.
    • Place the pots in a sunny spot in the lab and water the soil daily, until it is just damp.
    • When the eggs arrive, place the egg strips egg-side down on different radish leaves. Note: Under indirect sunlight or indoor light, the eggs will hatch in around 48 - 72 hours.
    • When the caterpillars reach their fourth instar growth stage, transfer them onto a cabbage for three days, taking care to mist the caterpillars occasionally with water to prevent drying.

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