Phenomenon
Organisms live in constantly changing environments but living cells can only survive within a narrow range of conditions (temperature, pH, concentrations of substances etc.).
Question
How does the body continue to function under different circumstances (exercise, extreme heat or cold)?
Model Ideas
- Organisms have feedback mechanisms consisting of structures that:
- sense conditions in the environment
- process the information
- direct responses needed to bring the conditions back to the optimal range for that organism, or to cause an event to occur.
- information can be carried electrically (neural), chemically (hormonal), or both.
Overview
Transition in: We know some important chemical processes necessary for survival. But how do organisms maintain the necessary conditions in their cells for these processes to occur? How do our bodies ensure that needed materials are provided, waste products are removed, and appropriate temperatures are maintained?
Cells need steady supplies of materials and stable internal conditions in a constantly changing environment. In this segment students develop a model to explain how organisms sense changes in external and internal conditions and adjust to meet the needs of cells.
A simple activity where students monitor their own heart rates establishes the phenomenon: exercise increases heart rate, while resting decreases. Once they see the pattern students generate questions. Questions should focus on why we see this pattern or how the body makes these adjustments. The class reasons together to figure out the “why”. Then students work in pairs with a reading and manipulatives to figure out the “how”. We build a diagram for heart rate regulation and use it to generate a generic model of a feedback loop to apply to other situations, like heat regulation.
Transition out: We now know how we get energy needed to survive and matter needed to grow and maintain our bodies, and how our bodies maintain conditions needed for these processes to occur. Now that we've figured out how matter and energy are regulated within an organism we go on to consider how matter and energy flow between organisms.
Advanced Planning
Prepare sets of manipulatives for each group for the Heart Rate activity.
See Optional Topics for materials and preparation required for each.
We've provided links to one teacher's versions of these topics that are important but outside the main MBER map.
OPTIONAL TOPIC 1: MICROSCOPES (click for resources) [hyperlink is microscope skills on old site; need to be fixed] The microscope is a basic tool of biology. If you want students to see cells, microorganisms etc. with their own eyes, they need to know how to use microscopes.
OPTIONAL TOPIC 2: CELLS (click for resources) [hyperlink needs to be fixed to go to cells] Cell theory is one of just three, perhaps two (along with Natural Selection and the formerly lauded, now complicated "Central Dogma" that connects genes to proteins across life) that organize our knowledge of living things. Although cells are not directly addressed in the DCI's, understanding cell structure and function provides valuable context for our explorations of the processes of life. The materials on cells provided here emphasize a comparative, evolutionary approach that deepens student understanding of natural selection and provides further evidence for the unity and diversity of life.
OPTIONAL TOPIC 3: ENZYMES (click for resources) [hyperlink nonexistent] In Cellular Respirations students learned that energy-releasing chemical reactions require activation energy. Now we ask them to contemplate how it is possible for reactions to start in a cell. The materials provided here include a lab that illuminates the nature and effects of environmental factors of enzymes. Also provided is a reading on enzymes. Awareness of the nature of enzymes and their environmental requirements provides a transition from chemistry into homeostasis and feedback mechanisms. Students who understand the dependence of life activities on enzymes will find it easier to comprehend how, simply by controlling protein production, DNA directs the life processes of organisms.
BUILDING A MODEL OF FEEDBACK LOOPS
1. We ask how can a body continue to function even in extreme circumstances like intense physical exercise, extreme hot or cold?
We understand that when you exercise your body responds in different ways.
2. We measure our heart rate at rest and after exercising so we can collect data and look for patterns. This will provide some personal phenomena.
We collected data on our own heart rates before and after exercise and observed that heart rate is low before exercise, goes up after exercise, then goes down again after resting.
3. Now we have our phenomena and we ask, what questions would a scientist have about the patterns that you’ve identified?
We have a driving question that will focus our model development.
4. We ask for initial ideas about how our heart rate speeds up after exercise and then slow down.
We put our initial ideas on the table so that we can examine them in more detail.
5. We guide the students through a series of questions to help us think about the heart and it’s connection to the body.
We learned or perhaps reviewed the function of the heart which is to deliver food and oxygen to the cells for fuel for cellular respiration and thus energy.
6. We ask how a body can maintain itself when it is put through extremes like the biggest loser did when he exercised.
We understand that the heart delivers food and oxygen to the cells and that when we exercise this delivery increases to provide more energy for the muscle cells. When we stop exercising the delivery can slow down because we do not need as much fuel for energy via cellular respiration.
7. We have been focusing on why the heart rate increases when we exercise. Now we look at how it all happens.
We figure out that body has a series of systems that help regulate heart rate.
8. We use our diagram from the manipulative activity on how the body controls heart rate, and our model to write an explanation to our driving question.
We wrote an explanation that explains how the body regulates heart rate.
9. Now we introduce the term “feedback loop”. The generic feedback diagram handout includes the general terms for the important components of feedback loops. Have students note on their handouts the specific structures in the heart rate feedback loop that plays the role of each of these components.
We learned that this regulatory function is called Feedback Loops and that there is a general components to feedback loops that can be applied to different situations.
10. Now that we have a model for feedback loops, we ask students to map the phenomenon “when we get hot, we sweat” onto a blank loop. Students won’t know all the pieces but that is fine. We just ask them to do as much as they can so they will see that it works for examples. You could choose a different phenomenon, or do several.
We can apply our model for feedback loops to other phenomena.
Download Resources
| Attachment | Size |
|---|---|
| All MBER-Bio Feedback Loops Materials (Download) | 35.01 MB |