1. Decomposers Unit Digestion and Biosynthesis
Image Credit: Craig Douglas, Michigan State University

2. Food in dead organisms is mostly water and large organic molecules
Image Credit: Craig Douglas, Michigan State University
Use the bread mold investigation results to ask about how decomposers grow.
Use slides 4-6 to pose the question that they will answer in this activity: How can decomposers make their molecules from food molecules?
Optional: Using the instructional model poster, remind students that they are at the “top of the triangle” in the unit: they have observed animals eating food at a macroscopic scale during inquiry (going up the triangle), and now they will use that information to talk about how this happens at an atomic-molecular scale using application (going down the triangle).
Tell students although they couldn’t measure it, the bread mold gained weight. Tell them that today’s activity is designed to help them explain how decomposers grow and gain weight. In this activity, they will be talking about a mushroom instead of a bread mold. They will come back to bread mold at the end of the unit.
Use slides 2-3 to discuss what decomposers use dead organisms as food, how they do take in all dead organisms as food and how decomposers food in two ways—for growth and energy. In this activity they will model the chemical processes involved in growth.
Use slides 4-6 to remind students of the molecules mushrooms are made of (this will be review from the previous activity).
Use slide 6 to ask: How can fungi make their molecules from food molecules?
Cellulose
Plant protein
…and many other polymers

3. Fungi are mostly water and different large organic molecules
Mushroom protein
Starch
…and many other polymers
Image Credit: Craig Douglas, Michigan State University
Use the bread mold investigation results to ask about how decomposers grow.
Use slides 4-6 to pose the question that they will answer in this activity: How can decomposers make their molecules from food molecules?
Optional: Using the instructional model poster, remind students that they are at the “top of the triangle” in the unit: they have observed animals eating food at a macroscopic scale during inquiry (going up the triangle), and now they will use that information to talk about how this happens at an atomic-molecular scale using application (going down the triangle).
Tell students although they couldn’t measure it, the bread mold gained weight. Tell them that today’s activity is designed to help them explain how decomposers grow and gain weight. In this activity, they will be talking about a mushroom instead of a bread mold. They will come back to bread mold at the end of the unit.
Use slides 2-3 to discuss what decomposers use dead organisms as food, how they do take in all dead organisms as food and how decomposers food in two ways—for growth and energy. In this activity they will model the chemical processes involved in growth.
Use slides 4-6 to remind students of the molecules mushrooms are made of (this will be review from the previous activity).
Use slide 6 to ask: How can fungi make their molecules from food molecules?
How can fungi make their molecules from food molecules in dead organisms?

4. How can fungi digest food without mouths or intestines (digestive systems)?
Image Credit (mushroom graphic): Craig Douglas, Michigan State University
Image Credit (mushroom photographs): Hannah Miller, Michigan State University
Ask students for their ideas about how mushrooms can digest food without digestive systems.
Show students slide 7 and tell students that like animals, fungi have to digest their food, but how can they do that if they don’t have mouths, stomachs, or intestines?
Show students more time-lapse videos of decomposer growth (we recommend the bagel or strawberry videos) or the (Optional) National Geographic podcast. Ask them to notice the structure of the fungi, and to think about where digestion might be happening.
Show slide 8 and ask students to examine the structure of a mushroom. Explain that a mushroom is the fruiting body of a fungus (sort of like the apple on an apple tree). It spreads spores from the fungus to other places where fungi can grow. The main body of the mushroom is called the mycelium; it is an underground network of thin fibers called hyphae.
Click to show the arrow on slide 8 and tell students fungi digest food outside their bodies by secreting digestive enzymes from cells in the hyphae that break polymers down into monomers that can be absorbed by cells in the hyphae.

5. The structure of fungus
Image Credit: Craig Douglas, Michigan State University
Ask students for their ideas about how mushrooms can digest food without digestive systems.
Show students slide 7 and tell students that like animals, fungi have to digest their food, but how can they do that if they don’t have mouths, stomachs, or intestines?
Show students more time-lapse videos of decomposer growth (we recommend the bagel or strawberry videos) or the (Optional) National Geographic podcast. Ask them to notice the structure of the fungi, and to think about where digestion might be happening.
Show slide 8 and ask students to examine the structure of a mushroom. Explain that a mushroom is the fruiting body of a fungus (sort of like the apple on an apple tree). It spreads spores from the fungus to other places where fungi can grow. The main body of the mushroom is called the mycelium; it is an underground network of thin fibers called hyphae.
Click to show the arrow on slide 8 and tell students fungi digest food outside their bodies by secreting digestive enzymes from cells in the hyphae that break polymers down into monomers that can be absorbed by cells in the hyphae.

6. Food molecules are dead things like stumps
Place marker here: large food molecules (dead stuff) here in trunk
Image Credit: Craig Douglas, Michigan State University
Overview the process of external digestion in fungi.
Give each pair of students a Decomposer 11 x 17 Poster and a penny. Have students put their penny in the trunk (slide 9). Use slide 10 to remind students that decomposers use their food in two ways: materials for growth (biosynthesis) and energy (cellular respiration), but that digestion has to happen before either of those processes can occur.
Use slides to show students what happens to the food that is digested: Large organic molecules (polymers) are divided into small organic molecules (monomers) outside the fungi’s body.
Optional: Display the following posters in your classroom to help students visualize the digestion of polymers to monomers.
Carbohydrates: Use the Digestion and Biosynthesis of Carbohydrates 11 x 17 Poster to offer students a visualization of how polymers like starch (which is a type of carbohydrate) are broken apart into monomers like glucose.
Proteins: Use the Digestion and Biosynthesis of Protein 11 x 17 Poster to offer students a visualization of how polymers like proteins are broken down into monomers like amino acids.

7. Step 1: Digestion Materials for growth: Biosynthesis Food Digestion
Energy: Cellular respiration
Credit: Craig Douglas, Michigan State University
Overview the process of external digestion in fungi.
Give each pair of students a Decomposer 11 x 17 Poster and a penny. Have students put their penny in the trunk (slide 9). Use slide 10 to remind students that decomposers use their food in two ways: materials for growth (biosynthesis) and energy (cellular respiration), but that digestion has to happen before either of those processes can occur.
Use slides to show students what happens to the food that is digested: Large organic molecules (polymers) are divided into small organic molecules (monomers) outside the fungi’s body.
Optional: Display the following posters in your classroom to help students visualize the digestion of polymers to monomers.
Carbohydrates: Use the Digestion and Biosynthesis of Carbohydrates 11 x 17 Poster to offer students a visualization of how polymers like starch (which is a type of carbohydrate) are broken apart into monomers like glucose.
Proteins: Use the Digestion and Biosynthesis of Protein 11 x 17 Poster to offer students a visualization of how polymers like proteins are broken down into monomers like amino acids.

8. Food is digested by fungal enzymes outside the fungi’s body
Keep marker here: Large food molecules break into small molecules outside fungi’s body
Image Credit: Craig Douglas, Michigan State University
Overview the process of external digestion in fungi.
Give each pair of students a Decomposer 11 x 17 Poster and a penny. Have students put their penny in the trunk (slide 9). Use slide 10 to remind students that decomposers use their food in two ways: materials for growth (biosynthesis) and energy (cellular respiration), but that digestion has to happen before either of those processes can occur.
Use slides to show students what happens to the food that is digested: Large organic molecules (polymers) are divided into small organic molecules (monomers) outside the fungi’s body.
Optional: Display the following posters in your classroom to help students visualize the digestion of polymers to monomers.
Carbohydrates: Use the Digestion and Biosynthesis of Carbohydrates 11 x 17 Poster to offer students a visualization of how polymers like starch (which is a type of carbohydrate) are broken apart into monomers like glucose.
Proteins: Use the Digestion and Biosynthesis of Protein 11 x 17 Poster to offer students a visualization of how polymers like proteins are broken down into monomers like amino acids.

9. During digestion, large organic molecules are broken down into small organic molecules
LARGE = Polymer
SMALL = Monomers
Image Credit: Craig Douglas, Michigan State University
Overview the process of external digestion in fungi.
Give each pair of students a Decomposer 11 x 17 Poster and a penny. Have students put their penny in the trunk (slide 9). Use slide 10 to remind students that decomposers use their food in two ways: materials for growth (biosynthesis) and energy (cellular respiration), but that digestion has to happen before either of those processes can occur.
Use slides to show students what happens to the food that is digested: Large organic molecules (polymers) are divided into small organic molecules (monomers) outside the fungi’s body.
Optional: Display the following posters in your classroom to help students visualize the digestion of polymers to monomers.
Carbohydrates: Use the Digestion and Biosynthesis of Carbohydrates 11 x 17 Poster to offer students a visualization of how polymers like starch (which is a type of carbohydrate) are broken apart into monomers like glucose.
Proteins: Use the Digestion and Biosynthesis of Protein 11 x 17 Poster to offer students a visualization of how polymers like proteins are broken down into monomers like amino acids.
STARCH
GLUCOSE (SUGAR)

10. Breakdown Protein Molecules (Digestion)
Let’s focus on what happens to PROTEIN in food.
(Put the other food molecules to the side for now.)
Digest PROTEIN molecules by cutting the protein into individual amino acids.
Notice that after you cut the protein apart there are bonds without atoms. Cut up water molecules to tape an –H and –OH to every amino acid.
Image Credit: Craig Douglas, Michigan State University
Have students set up their reactants and model digestion.
Give each pair of students a Molecular Models 11 x 17 Placemat, one set of Forms of Energy Cards, one pair of scissors, a removable tape dispenser, and one protein molecule, one carbohydrate molecule, and five water molecules (from the 3.2 Polymers for Cutting Handout).
Have students place a “chemical energy card” on the reactants side of their placemat, along with their water, protein and carbohydrate molecules.
Coach students to simulate the process of hydrolysis by cutting a water molecule each time they make a cut in the polymer. This helps show that each time a bond between two monomers is broken, the chemical reaction requires water and new bonds form.
Protein: Show slide 14. Have students cut one protein polymer into amino acid monomers. Then, cut the water molecules and attach an –H and an –OH to each amino acid. Watch the animation on slides
Carbohydrate: Show slide 17. Have students cut one starch polymer (a type of carbohydrate) into glucose monomers. Then cut the water molecules and attach an –H and an –OH to each glucose. Watch the animation on slides
Have students move the new molecules with the energy card to the products side of their placemat. When watching the slides, ask students what is happening to energy. Listen to see if they notice that chemical potential energy is conserved through digestion.
Chemical change

11. Breakdown of Starch Molecules (Digestion)
Digest STARCH molecules by cutting the starch into individual glucose monomers.
Notice that after you cut the starch apart there are bonds without atoms. Cut up water molecules to tape an –H and –OH to every glucose.
Chemical change
Image Credit (molecule): Craig Douglas, Michigan State University
Have students set up their reactants and model digestion.
Give each pair of students a Molecular Models 11 x 17 Placemat, one set of Forms of Energy Cards, one pair of scissors, a removable tape dispenser, and one protein molecule, one carbohydrate molecule, and five water molecules (from the 3.2 Polymers for Cutting Handout).
Have students place a “chemical energy card” on the reactants side of their placemat, along with their water, protein and carbohydrate molecules.
Coach students to simulate the process of hydrolysis by cutting a water molecule each time they make a cut in the polymer. This helps show that each time a bond between two monomers is broken, the chemical reaction requires water and new bonds form.
Protein: Show slide 14. Have students cut one protein polymer into amino acid monomers. Then, cut the water molecules and attach an –H and an –OH to each amino acid. Watch the animation on slides
Carbohydrate: Show slide 17. Have students cut one starch polymer (a type of carbohydrate) into glucose monomers. Then cut the water molecules and attach an –H and an –OH to each glucose. Watch the animation on slides
Have students move the new molecules with the energy card to the products side of their placemat. When watching the slides, ask students what is happening to energy. Listen to see if they notice that chemical potential energy is conserved through digestion.

12. Where do digested monomers go?
glucose
fatty acid
Image Credit: Craig Douglas, Michigan State University
Use the poster to show how food molecules move into cells.
Use Slides to show how monomers then move through the fungi after digestion occurs.
Explain that outside the fungi, the protein (and starch and fat) is completely broken down into monomers by enzymes that were excreted by the fungi. (In humans and other animals, fiber is not broken down. But fungi can digest fiber.)
Explain to students that small molecules can move across cell membranes in fungi bodies, but large molecules cannot. Only small molecules move through the hyphae and mycelium.
Use slide 22 to transition students from digestion to biosynthesis.
glycerol
amino acid

13. Digested monomers enter the hyphae and move to all parts of fungal bodies.
Image Credit: Craig Douglas, Michigan State University
Use the poster to show how food molecules move into cells.
Use Slides to show how monomers then move through the fungi after digestion occurs.
Explain that outside the fungi, the protein (and starch and fat) is completely broken down into monomers by enzymes that were excreted by the fungi. (In humans and other animals, fiber is not broken down. But fungi can digest fiber.)
Explain to students that small molecules can move across cell membranes in fungi bodies, but large molecules cannot. Only small molecules move through the hyphae and mycelium.
Use slide 22 to transition students from digestion to biosynthesis.

14. Decomposers use food in two ways
Materials for growth: Biosynthesis
Food
Digestion
Energy: Cellular respiration
Credit: Craig Douglas, Michigan State University
Use the poster to show how food molecules move into cells.
Use Slides to show how monomers then move through the fungi after digestion occurs.
Explain that outside the fungi, the protein (and starch and fat) is completely broken down into monomers by enzymes that were excreted by the fungi. (In humans and other animals, fiber is not broken down. But fungi can digest fiber.)
Explain to students that small molecules can move across cell membranes in fungi bodies, but large molecules cannot. Only small molecules move through the hyphae and mycelium.
Use slide 22 to transition students from digestion to biosynthesis.

15. Small molecules are taken up by fungal hyphae
Keep marker here: Small food molecules are taken up by hyphae.
Image Credit: Craig Douglas, Michigan State University
Have students use their poster to model the movement of molecules.
Use slides to prompt students to move the penny through the fungal hyphae to the mushroom, one place where biosynthesis occurs. Note: biosynthesis occurs in all cells, but here we use a mushroom as an example.

16. Small molecules are transported by fungal hyphae
Move Marker through fungal hyphae: the small molecules through the fungal hyphae
Image Credit: Craig Douglas, Michigan State University
Have students use their poster to model the movement of molecules.
Use slides to prompt students to move the penny through the fungal hyphae to the mushroom, one place where biosynthesis occurs. Note: biosynthesis occurs in all cells, but here we use a mushroom as an example.

17. Keep marker here: large molecules built here
Biosynthesis is the process of small organic molecules becoming large organic molecules in all body parts
Keep marker here: large molecules built here
Image Credit: Craig Douglas, Michigan State University
Have students use their poster to model the movement of molecules.
Use slides to prompt students to move the penny through the fungal hyphae to the mushroom, one place where biosynthesis occurs. Note: biosynthesis occurs in all cells, but here we use a mushroom as an example.

18. What’s in fungi (Mushroom)?
PROTEIN STARCH
Mushrooms
Image Credit (molecule): Craig Douglas, Michigan State University
Make the transition from digestion to biosynthesis.
Ask students for ideas about what might happen to the smaller food molecules once they are in the cells. Listen for ideas.
Show slide 26 to remind students of the information they learned from nutritional labels: mushrooms are made primarily of protein (3g) and carbohydrates (8g). This means that the cells in the mushroom are going to make protein and carbohydrate molecules so the mushrooms cells can grow bigger and divide.
Tell students that they will use the placemat and molecules to model the process of biosynthesis, which is what happens when decomposers build large organic molecules from small ones.
Point out that when they are modeling, they should remember that during biosynthesis, no "high energy" C-C or C-H bonds will be made or broken. The chemical energy is conserved!
(Optional) Refer to the Digestion and Biosynthesis posters in your classroom to help students visualize the biosynthesis of monomers to polymers.

19. Build a Mushroom (Biosynthesis)
Build PROTEIN molecules by taping 4 amino acid monomers.
Notice you will need to remove an –H and –OH from each amino acid. Tape these back together to make water.
Chemical change
Image Credit (molecule): Craig Douglas, Michigan State University
Have students set up their reactants and model biosynthesis.
Have students place a “chemical energy card” on the reactants side of their placemat, along with their amino acids and glucose molecules. Coach students to simulate the actual process of dehydration synthesis by making a water molecule each time they tape two monomers together. This helps show that each time a bond is broken a chemical reaction takes place and new bonds form.
Protein: Show slide 27. Have students tape together four amino acid monomers to form one protein polymer and three water molecules. Then, watch the animation on slides
Carbohydrate: Show slide 30. Have student tape together three glucose monomers to form one starch monomer and two water molecules. Then, watch the animation on slides
Have students move the new molecules with the energy card to the products side of their placemat. Ask students what is happening to energy during biosynthesis. Listen to see if they notice that chemical potential energy is conserved through the chemical change.
If time allows make the connection to cell division: cells have to both get bigger and also divide in order for fungi to grow. This is why decomposers perform biosynthesis: to make cells get bigger (growth) so they can divide.

20. Build a Mushroom (Biosynthesis)
Build STARCH molecule by taping 3 glucose monomers together.
Notice you will need to remove an –H and –OH from glucose. Tape these back together to make water.
Chemical change
Image Credit (molecule): Craig Douglas, Michigan State University
Have students set up their reactants and model biosynthesis.
Have students place a “chemical energy card” on the reactants side of their placemat, along with their amino acids and glucose molecules. Coach students to simulate the actual process of dehydration synthesis by making a water molecule each time they tape two monomers together. This helps show that each time a bond is broken a chemical reaction takes place and new bonds form.
Protein: Show slide 27. Have students tape together four amino acid monomers to form one protein polymer and three water molecules. Then, watch the animation on slides
Carbohydrate: Show slide 30. Have student tape together three glucose monomers to form one starch monomer and two water molecules. Then, watch the animation on slides
Have students move the new molecules with the energy card to the products side of their placemat. Ask students what is happening to energy during biosynthesis. Listen to see if they notice that chemical potential energy is conserved through the chemical change.
If time allows make the connection to cell division: cells have to both get bigger and also divide in order for fungi to grow. This is why decomposers perform biosynthesis: to make cells get bigger (growth) so they can divide.

21. What happens to food monomers that are not used in biosynthesis?
Image Credit: Craig Douglas, Michigan State University
Discuss other ways fungi use sugar monomers.
Use slides to discuss with students that not all food monomers are used in biosynthesis.
Show slide 33 and ask students: What happens to food monomers that are not used in biosynthesis?
Use slide 34 to transition from biosynthesis to cellular respiration.

22. Decomposers use food in two ways
Materials for growth: Biosynthesis
Food
Digestion
Energy: Cellular respiration
Credit: Craig Douglas, Michigan State University
Discuss other ways fungi use sugar monomers.
Use slides to discuss with students that not all food monomers are used in biosynthesis.
Show slide 33 and ask students: What happens to food monomers that are not used in biosynthesis?
Use slide 34 to transition from biosynthesis to cellular respiration.