NGSS and Feedback Loops

Probably one of the strangest of all the Next Generation Science Standards is  HS-LS1-3 :  Plan and conduct an investigation to provide evidence that feedback mechanisms maintain homeostasis.

One of the reasons I find this standard to be curious is that all of the other standards present fairly general statements about what knowledge students are expected to have regarding topics like photosynthesis and inheritance.   This is the ONLY standard that asks students to plan and conduct what appears to be a very specific experiment regarding feedback mechanisms.

Within the evidence statements of NGSS, the standard is clarified to provide examples of what kinds of experiments would qualify:

  • heart rate response to exercise
  • stomate response to moisture and temperature
  • root development in response to water levels

I would also add that many of the traditional experiments you might already be doing in biology could qualify, like this popular lab freshman biology students do: “Observation of a Living Earthworm,” which includes an investigation where students  determine if the earthworm prefers a moist or dry environment.  The AP Biology Lab on Cellular respiration would also qualify as students determine that warmer temperatures will increase the rate of respiration.    Basically, any investigation that includes an organism’s response to an environmental condition could work to address this standard.   Though you probably want to include the the idea of feedback loops within the post-lab discussion if that term is not specifically included in the lab guide.

thyroid pathwayThe problem with this standard is that when students are asked to demonstrate mastery on a standardized test, they aren’t going to be designing and conducting an experiment.  Instead, they are probably going to be given a short paragraph that describes and experiment, followed by some data to analyze and questions that ask them to explain what happened.   The assessment rubric will probably look for answers with terms like feedback loops and homeostasis.   It is also likely that the test will have a much more complicated experiment than one on earthworm preference for moisture.   Feedback loops are very relevant in anatomy and in particular the endocrine system.    The heart rate and exercise lab is great for a class starter, but isn’t a really challenging investigation for older biology and anatomy students.

When studying the endocrine system, I have my students look at a much more challenging scenario involving negative feedback loops and the thyroid gland.  In this case study, “What’s Wrong with Timothy?” students examine the symptoms related to dysfunction of the thyroid and how the pituitary and thalamus attempt to restore the body’s homeostasis.   In Timothy’s case, this proved difficult due to a tumor on the pituitary gland, the gland that specifically regulates all of the other endocrine glands.

While students aren’t technically planning and conducting an investigation, they are analyzing data and using models to gain an understanding of feedback loops and homeostasis, which is more likely to help them on the Big Standardized test than the heart rate and exercise activity.


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