Next Generation Science Standards

Performance Expectation

Construct and revise an explanation based on evidence for how carbon, hydrogen, and oxygen from sugar molecules may combine with other elements to form amino acids and/or other large carbon-based molecules.

• Clarification Statement: Emphasis is on using evidence from models and simulations to support explanations.
• Assessment Boundary: Assessment does not include the details of the specific chemical reactions or identification of macromolecules.

People tend to associate metabolism with weight, where people with a "high metabolism" can eat whatever they want and not gain an ounce. It's also said that metabolism slows with age. Wouldn't it be nice to be teenagers again so we could pack in a couple double cheeseburgers or a pint of Ben and Jerry's without consequence? Presumably, our bodies were better able to "burn off" those extra calories so they didn't accumulate as fat. Great.

But what underlies our bodies' fantastic ability to take in food and use it to power our lives and build the components that we need to live until we find that next donut? The metabolic processes of catabolism and anabolism work together through a number of pathways to break down sugars (and proteins, fats, etc. that aren't specifically covered by this performance expectation) into smaller compounds, which are then used to build protein, nucleic acids, and other vital macromolecules. Striking a balance between catabolism and anabolism is therefore really important to staying healthy. We literally are what we eat.

Straight up, teaching this topic is challenging, but the goal with this performance expectation is to focus on the big picture concepts. Students who master this performance expectation need to be able to construct and revise an explanation based on evidence about metabolism. It's up to you how deep down the metabolic rabbit hole you choose to go, but students should be able to find, evaluate, and use evidence to explain how sugar becomes protein, nucleic acids, and lipids.

Here are some activity ideas to get your students to break down this material and synthesize it on their own:

• Break students into expert jigsaw groups and then assign each one group one subset of cellular respiration. Once they're all experts, split the groups up and have one member of each group teach the others what they learned.
• Tell students they're auditioning to be the host of a new science show. Have students first write a script for their explanation of how carbon-based molecules are formed inside an organism. Once they have their script, pair the students up and have them do peer reviews and make any revisions to their script as necessary. Time permitting, you can then have your students film each other reading their scripts.
• It's anthropomorphisation time. Have your students draw a comic strip illustrating how an amino acid, nucleic acid, or lipid is formed. Bonus points if they make it dramatic and show a steamy affair between glucose and ATP during glycolysis. Once they're done drawing, have them write a paragraph or two of "notes from the artist" explaining their sources of inspiration (i.e., evidence/sources), what worked well in their comic, and what aspects of the process they could have depicted better if they were as good as Steve Ditko.

Disciplinary Core Ideas

LS1.C – Organization for Matter and Energy Flow in Organisms: The sugar molecules thus formed contain carbon, hydrogen, and oxygen: their hydrocarbon backbones are used to make amino acids and other carbon-based molecules that can be assembled into larger molecules (such as proteins or DNA), used for example to form new cells.

Metabolism is like recycling. After glucose is broken down and energy is made, the chemical intermediates and products are shuttled off and used as building blocks to make new essential molecules. Students should know that amino acids in particular aren't all made the same way, but their hydrocarbon backbones come from the sugars we eat and break down.

Gathering evidence of this recycling most often requires scientists to use radioactive tracers to track the chemicals through their journey from sugar to macromolecule. Also called radioactive labeling, this method provides a direct means of looking at the source and destination of carbon, hydrogen, and oxygen.

Learning about the use of hydrogen and oxygen tracers in plants is one way to make sense of metabolism, but feel free to incorporate any other suitable evidence or learning devices you think will work with your group of students.

LS1.C – Organization for Matter and Energy Flow in Organisms: As matter and energy flow through different organizational levels of living systems, chemical elements are recombined in different ways to form different products.

In the context of this performance expectation, it may be helpful to teach students about the chemical structures of some biological molecules and how they are changed in chemical reactions. Again, though, the goal here isn't to make students memorize specific chemical reactions or biomolecules, but seeing some examples of how matter and energy flows will help ground students with the process in general.

Organisms are extremely crafty at recombining chemical intermediates and products to minimize their need to get more materials from the environment. They also extract the maximum amount of energy from food, which is why you might want to think twice before downing that entire plate of bacon.

Science and Engineering Practices

Constructing Explanation and Designing Solutions: Construct and revise an explanation based on valid and reliable evidence obtained from a variety of sources (including students' own investigations, models, theories, simulations, peer review) and the assumption that theories and laws that describe the natural world operate today as they did in the past and will continue to do so in the future.

The main goal of this performance expectation is that students can explain on their own how sugar molecules are broken down in organisms and are used to create amino acids. To do that, shower them with all different types of evidence, activities, and sources so they can synthesize the concepts in their brains first.

From there, they should make the connection that the processes of metabolism power organisms large and small, and it's been doing so for billions of years. If need be, give 'em a little nudge in this direction to make that connection.

Their own explanation can come in many forms, so direct students in whatever direction you think appropriate, be it a traditional paper or something more creative like a video, presentation, animation, or a live action melodrama of catabolism.

Crosscutting Concepts

Energy and Matter: Changes of energy and matter in a system can be described in terms of energy and matter flows into, out of, and within that system.

In traditional Chinese culture, qi (pronounced chi) is the energy flow within every living thing. This is a beautiful way of thinking about the flow of energy (and matter) through a biological system. In physiology, metabolism is what does the moving and shaking of matter and energy. To maintain homeostasis, they flow in a steady state through the body and are close to, but never at chemical equilibrium—keeping metabolic processes going.

In the context of this performance expectation, the take-home message is this: the body takes energy and matter from food and uses it to power, build, and repair itself, and to store energy away for later. Phew. Is it time for that qi burger yet?