Decomposers Lesson 2 Background Information

Lesson 2 focuses on essential foundational knowledge that students will need to achieve the objectives for this unit. In this lesson students learn to read nutrition labels to identify the key materials in the foods we eat, which are also the materials in plant and animal bodies. The activities in this lesson serve as the Foundational Knowledge and Practice Phase of the Instructional Model, where students are introduced to key ideas and practices that they will use throughout the rest of the Decomposers unit.

In Activity 2.1, students review the anatomy of a molecule using the Molecule 11 x 17 Poster to refresh their memory of the precise use of words we use to describe matter at the atomic-molecular scale. Then, students examine nutritional labels to learn that there are three broad classes of materials in food:

• Organic materials, including fats, proteins and carbohydrates (sugars, starches, and indigestible fibers such as cellulose). These are the key materials that make up biomass (everything but water) of all living things and are essential for life.
• Vitamins and minerals, including sodium, iron, calcium, and many others. These materials are also essential for life, but only in small amounts—less that 1% of almost all foods.
• Water is not listed on nutrition labels, but it makes up more than 50% of the mass of almost all plant and animal bodies and almost all the foods we eat. Students can figure out how much of a food is water by subtracting the mass of the organic matter from the total serving size (100 grams for all the nutrition labels used in this lesson).

Activity 2.2 uses nutrition labels as the basis for a simplified account of the materials that foods—and the living organisms that foods come from—are made of. All living things are made of thousands of different substances, all created by the plants from glucose, water, and soil minerals. Carbon TIME units emphasize the most important of these macromolecules: polysaccharides (including starch and cellulose), fats or lipids, and proteins. Many other essential macromolecules such as nucleic acids are left for more advanced treatments.

The large organic molecules (sometimes called macromolecules) in plants, animals, and decomposers are actually much larger than the molecules shown in the presentation and modeling activity:

• Fatty acids typically contain 10 to 25 carbon atoms.
• Proteins can consist of hundreds of amino acids. Humans are typical of many organisms in that our proteins contain 21 different kinds of amino acids.
• Starch and cellulose molecules can be made of hundreds or thousands of sugar monomers. Different kinds of starch and fiber can also include other 5-carbon and 6-carbon sugars besides glucose.

Although we hope that students will come to appreciate the vast number and complexity of biomolecules, our emphasis in Carbon TIME is on helping students understand that all of this complexity arises from a simple starting point—glucose and minerals—and a few simple chemical processes in biosynthesis.

Although there are obvious differences in the chemical composition of plants, animals, and decomposers, the Carbon TIME units emphasize their similarities. Most of the monomers (sugars or monosaccharides, amino acids, fatty acids and glycerol) in all living things are created in plants and made into polymers by the plants. Animals and decomposers break these polymers back down into monomers through the process of digestion, then alter the monomers and build new polymers through their own biosynthesis.

In activity 2.3, students take a short quiz to check their knowledge of these concepts before applying these ideas throughout the rest of the Unit.

In activity 2.4, students begin to consider questions about cells related specifically to decomposers, which they will study throughout the unit.

Key Carbon-Transforming Processes: Photosynthesis, Cellular Respiration, & Biosynthesis