Phenomenon
We examine several different ways that organisms add matter to their bodies and we wonder where it goes when that matter is “lost”.
Question
- How do we get matter for body parts from food?
- Worded more specifically it could be something like: “How do we make things like hair from eating beans or potato chips?”
- How do we make new carbohydrates, fats and proteins?
- What happens when we take in more food than our body can use?
- What happens to fat and protein when they enter the body?
- Are carbohydrates the only fuel for energy?
- How do we store energy?
- What happens when an organism loses weight?
Model Ideas
As we move through the remainder of the Red Model Sequence and develop ideas about matter and energy in organisms, we explicitly develop two models in parallel. In our work with cellular respiration, we primarily add ideas to a model for Energy from Food.
These models have been building since Chemical Reactions and so represent a fairly lengthy list of ideas. Be sure to track them publicly with your students as you move through the learning segments. Note that the wording of each statement should reflect those of your students. The target here is the idea. Try to honor student language. For more information, see the MBER Essential: Close Enough.
Matter from Food:
Ideas from Chemical Reactions (previous unit)
- Matter is conserved, neither created nor destroyed. Matter is rearranged in chemical reactions.
- Food has matter in the form of protein, carbs and fats- the same things we find our bodies are made of. We also take in matter as oxygen and water.
- Some of this matter is used in our body, but we take in much more matter than we need to use to grow or maintain body structures.
- Some of this matter (especially much of the water but also some indigestible material) basically passes through us.
Ideas from Cellular Respiration (previous unit)
- Some of this matter is really taken in for energy. It is rearranged to obtain energy in a reaction called cellular respiration. The products are expelled from the body as carbon dioxide and water.
New Ideas from Biosynthesis (this triangle)
- Some of our digested food is broken down and rearranged to build new macromolecules we use to repair tissue and to build new body tissue.
- Food consumed in excess of what we need for energy and growth/repair is converted to fat and stored.
Energy from Food:
Ideas from Chemical Reactions (previous unit)
- Energy is conserved, neither created nor destroyed. Energy is transformed in chemical reactions.
- When the reactants have more potential energy than the products, energy is released in the reaction (“downhill” reaction).
- Food has energy in the form of calories.
- Living things get energy by rearranging food and oxygen molecules.
Ideas from Cellular Respiration (previous unit)
- Living things rearrange food (specifically glucose - C6H12O6) and O2 into CO2 and H2O
- (C6H12O6 + O2) have higher energy than (CO2 + H2O) so this rearrangement releases energy.
- The rearrangements occur in a series of steps rather than all at once.
- Collectively the reactions are called cellular respiration.
- Usable cellular energy is released in the form of ATP.
- UNITY AND DIVERSITY: Other reactions (such as fermentation) can produce biologically usable energy, but they are usually less efficient. We see these reactions in some groups of organisms that have evolved under different environmental conditions and in our own bodies during times when oxygen is not readily available.
New Ideas from Biosynthesis (this triangle)
- Building new biomolecules (proteins, fats and carbs) from the products of digestion requires energy (which is provided by cellular respiration).
- More generally, in chemical reactions where the products have more potential energy than the reactants, energy must be added to the reaction (“uphill” reaction).
- If you run out of glucose, your body can pull from fat stores—and then as a last resort, amino acids—to provide fuel for cellular respiration.
Overview
Transition in: The transition here is to now think about the matter from the food we eat. We know that not all of the food we eat is used for energy. What happens to the food not used for energy? What happens if we take in more food than we can use?
We now switch to thinking about the matter from the food we eat and how it is involved in cellular respiration. We ask, is it used for anything else? We quickly review relevant ideas from past models and readily recognize that the food we eat provides us with the components we need to build new body tissue.
We also review some ideas about digestion—that it breaks food first into carbs, fats and protein molecules, and then into their monomers. But now we explicitly discuss how some of our digested food is used to build new macromolecules and to repair existing or build new body tissue. We also figure out that the excess food that we take in is stored as fat. We then reason that our bodies can use fat for cellular respiration when we run out of glucose. Lastly, we recognize that building macromolecules requires energy or the “uphill” energy diagram. This is presented differently for the ethanol and electrolysis pathways, as this is the first time students who made sense of chemical reactions using ethanol have been exposed to the idea that some reactions require energy input. Lastly we discuss the idea of energy and matter cycles in organisms, tying several components of our Matter and Energy from Food models together.
When we return to our challenge question about the hibernating bear, we spend a bit of time making sure our ideas are consistent with our models. This is scaffolded by a Four Corners activity, several readings, review of key points from our earlier hibernating bear explanation. We then add to and revise our explanation through group writes, a gallery walk, and finally both group and whole class discussions. You may want to use some or all of these activities depending on your students’ level of understanding. As their final assessment, students now address a different phenomenon about weight gain and weight loss individually using their class models.
Transition out: We have fairly complete models for how we (and many other organisms) obtain matter and energy from food. But we have a number of lingering questions about plants? Do they eat food? How do they obtain matter and energy? We transition into our exploration of Photosynthesis at this point and ask a Challenge Question that is related to our models but perhaps not fully answered by them, "How does a seed grow into a tree?" Where did the matter (and energy) come from?
Download Resources
| Attachment | Size |
|---|---|
| All Resources for Biosynthesis | 24.41 MB |