Phenomenon
Living things need to take in matter to survive and get energy for life processes. It seems that matter is somehow rearranged inside our bodies because the outputs are different from the inputs.
Question
How do we get energy from food? How is the energy in food released in a form that can be used by cells in a way that does not harm them?
Model Ideas
As we move through the remainder of the Red Models Sequence and develop ideas about matter and energy flow 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.
Energy from Food (primary model here):
Model Ideas from Chemical Reactions
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).
[Electrolysis Classrooms Only: When the products have more potential energy than the reactants, energy must be added to the reaction (“uphill” reaction). ]
Food has energy in the form of calories.
Living things get energy by rearranging food and oxygen molecules.
New Model Ideas
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.
Matter from Food (secondary model here):
Model Ideas from Chemical Reactions
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.
New Model Ideas
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 (CO2 + H2O).
Overview
The goal is for students to develop a model that describes how food is rearranged through chemical reactions to form new molecules that can store and release energy.
Transition in: We've been exploring why we have to eat in order to survive. In the last model, we developed ideas around the role of chemical reactions in helping us obtain the matter and energy we need. In this model, we further develop ideas to explain HOW we get energy from food, culminating in the specific reaction of cellular respiration, the most ubiquitous and efficient way living things obtain energy.
After reviewing our understanding of how we gain both matter and energy from food, we dig deeper, trying to understand the chemical reactions that allow us to obtain the energy we need. Classrooms that burned ethanol in the prior unit have some experience of the energy gained by burning food and other fuels. We next explicitly link increased CO2 output (a sign of increase in the rate of the burning reaction) to increased energy demand during exercise and recognize we're on the right track.
So, what's the burning reaction inside our cells? We consider which components of food are the likely fuels and settle on glucose. We also learn that this particular reaction, called cellular respiration, happens in cell organelles called mitochondria. We reason that a one-step rearrangement would release enough energy to kill the cell, so we think about alternatives. The solution: a series of small rearrangements, each releasing a small, manageable amount of energy. We explain that in cellular respiration, energy is released as ATP, a sort of energy currency that can be directly used by cells to do work. But do all organisms do this? The investigation brings us back to thinking about the Unity and Diversity of life. Finally, we end by taking stock of what we have figured out so far about the role of food in living things.
Transition out: Though we have a pretty good understanding of the reactions involved in getting energy out of food, we realize we haven't gotten very far in terms of how the matter in food is used by our bodies to build and maintain them. In the next model, Biosynthesis, we more fully develop our model for Matter from Food.
Advanced Planning
MATERIALS NEEDED (besides basic lab equipment and supplies):
For the Exercise and Respiration Lab
(see CR 04 Exercise and Respiration Lab TEACHER GUIDE for quantities and details)
Materials:
- paper cup
- straw
- sodium carbonate solution
- phenolphthalein
- stopwatch / timer
For the CO2 Unity and Diversity Lab
(see CR 07 Do All Living Things Give Off CO2 TEACHER GUIDE for quantities and details)
Materials:
- phenol red
- club soda
- small test tubes and racks that will hold them
- corks or lids for the tubes
- screws
- forceps
- petri dish
- dropper bottles
- drinking straws
- radish seeds
- prep instructions:
- Soak 1/2 of them overnight before students set them up to sprout.
- Students put the soaked seeds in petri dishes to sprout [per directions in lab] the night before you do the procedure.
- yeast
- prep instructions:
- Mix with water and boil 1/2 of it for 10 minutes the night before the lab.
- medium crickets (one per group) - or you can have students bring their own
For Fermentation Lab
(see CR 07 Fermentation Lab TEACHER GUIDE for quantities and details)
Materials:
- narrow-mouth thermos bottles
- rubber stoppers for thermoses
- Erlenmeyer flasks
- two-hole rubber stoppers for flasks
- thermometers (unless you are using Pasco probes or something similar)
- glass tubing
- rubber tubing
Optional:
- bubble wrap to wrap around each thermos for additional insulation
- 2 electronic data collection devices (like Pasco Sparks – Fig. 5) with thin temp probe.
Download Resources
| Attachment | Size |
|---|---|
| All Resources for Cellular Respiration | 38.79 MB |