1. Carbon: Transformations in Matter and Energy
Environmental Literacy Project Michigan State University
Decomposers Unit Activity 5.1: Tracing the Processes of Fungi Growing: Digestion and Biosynthesis
Image Credit: Craig Douglas, Michigan State University

2. Unit map
You are here
Use the instructional model to show students where they are in the course of the unit.
Show slide 2 of the 5.1 Tracing the Processes of Fungi Growing: Digestion and Biosynthesis PPT.

3. Connecting Questions about Processes at Different Scales: Digestion
Unanswered Questions
Macroscopic Scale
How do fungi get food to all of their cells?
Microscopic Scale
How do food molecules get into the fungi’s hyphae?
Atomic-Molecular Scale
How are molecules in food changed chemically so that fungal cells can use them?
Discuss Connecting Questions about Processes at Different Scales for Digestion
Display slide 3 in the PPT. Show students the short clip of fungi growing. Follow the link in the PPT, in the materials list, or here (
Introduce students to the macroscopic driving question: How do fungi get food to all of their cells?
Connect this question at the macroscopic scale to an unanswered question at the microscopic scale: How do food molecules get into the fungi’s hyphae?
Connect this question at the microscopic scale to an unanswered question at the atomic-molecular scale: How are molecules in food changed chemically so that fungal cells can use them?
Assure students that we will be able to answer several of their unanswered questions by the end of today’s activity.

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
Have students consider how fungi can digest food without a digestive system.
Display slide 4 of the PPT and ask students to consider the question on the slide. 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? Ask them to notice the structure of the fungi, and to think about where digestion might be happening.
Show slide 5 of the PPT to point out where digestion occurs. 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.
Show slide 6 to introduce the idea the digestion occurs outside of the fungus.

5. The Structure of Fungus
Image Credit: Craig Douglas, Michigan State University
Have students consider how fungi can digest food without a digestive system.
Display slide 4 of the PPT and ask students to consider the question on the slide. 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? Ask them to notice the structure of the fungi, and to think about where digestion might be happening.
Show slide 5 of the PPT to point out where digestion occurs. 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.
Show slide 6 to introduce the idea the digestion occurs outside of the fungus.

6. How do fungi get food to all of their cells?
Materials for growth: Biosynthesis
Food
Digestion
Energy: Cellular respiration
Credit: Craig Douglas, Michigan State University
Have students consider how fungi can digest food without a digestive system.
Display slide 4 of the PPT and ask students to consider the question on the slide. 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? Ask them to notice the structure of the fungi, and to think about where digestion might be happening.
Show slide 5 of the PPT to point out where digestion occurs. 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.
Show slide 6 to introduce the idea the digestion occurs outside of the fungus.

7. Food molecules are dead things like stumps and detritus (organic molecules in soil)
Place one nickel here: large organic molecules in detritus in the soil
Image Credit: Craig Douglas, Michigan State University
Have students begin to trace the process of digestion in fungi.
Give each pair of students a Decomposer 11 x 17 Poster, 2 nickels and 10 pennies. Display slide 7 of the PPT.
Have students place one nickel in the tree trunk’s roots and one in the soil (very close to, but outside the hyphae). They should set their pennies to the side.
Explain that they will be using their nickels and pennies to trace the path of food in the fungi throughout the lesson.
Explain to students that the fungi can get organic molecules from the organic molecules in trees, from detritus in the soil, and other dead organisms.
Place one nickel here: large organic molecules (dead stuff) in tree

8. Food in dead organisms is mostly water and large organic molecules
Image Credit: Craig Douglas, Michigan State University
Remind students that what food is made up.
Display slide 8 to show students that dead organisms are mostly water and large organic molecules.
Cellulose
Plant protein
…and many other large organic molecules.

9. Food is digested by fungal enzymes outside a fungus’ body
Change nickel for five pennies: Large organic molecules break into small organic molecules outside a fungus’ body
Change nickel for five pennies: Large organic molecules break into small organic molecules outside a fungus’ body
Image Credit: Craig Douglas, Michigan State University
Tell students that the large organic molecules in dead organisms are broken down into small organic molecules during digestion outside of the fungi.
Display slide 9 of the PPT.
Explain to students that fungi release enzymes that break down large organic molecules into small organic molecules.
Have students represent this process by exchanging each of the nickels on the Decomposer 11 x 17 Poster for 5 pennies.

10. During digestion, large organic molecules are broken down into small organic molecules
STARCH
Image Credit: Craig Douglas, Michigan State University
Show what happens at the atomic-molecular scale.
Display slide 10 to show students large organic molecules are broken down into small organic molecules during digestion.
Show students the Digestion and Biosynthesis 11 X 17 Posters to help students visualize the process.
GLUCOSE (SUGAR)

11. What happens to carbon atoms and chemical energy in digestion?
Chemical change
Image Credit: Craig Douglas, Michigan State University
Show an animation of the process of digestion.
Display slide to show an animation of what happens to the molecules and chemical energy during digestion.
When watching the slides, ask students what is happening to energy. Listen to see if they notice that chemical potential energy is conserved in the C-C- and C-H bonds through digestion.
Large Organic
Molecules
(+ water)
Small Organic
Molecules
Reactants
Products

12. What happens to carbon atoms and chemical energy in digestion?
Chemical change
Image Credit: Craig Douglas, Michigan State University
Show an animation of the process of digestion.
Display slide to show an animation of what happens to the molecules and chemical energy during digestion.
When watching the slides, ask students what is happening to energy. Listen to see if they notice that chemical potential energy is conserved in the C-C- and C-H bonds through digestion.
Large Organic
Molecules
(+ water)
Carbon atoms stay in organic molecules with high-energy bonds
Small Organic
Molecules
Reactants
Products

13. Where do digested small organic molecules go?
glucose
Image Credit: Craig Douglas, Michigan State University
Show students where digested small organic molecules go in the body.
Use slides 13 and 14 to explain that the small organic molecules enter the hyphae and travel throughout all parts of a fungus’ body.
Show slide 15. Have students move their pennies into the hyphae on the Decomposer 11x17 Poster.
Show slide 16. Have students move the pennies from the tree trunk into the mushroom and the pennies from the soil detritus further into the hyphae.
glycerol
amino acid

14. Digested small organic molecules enter the hyphae and move to all parts of a fungus’ body.
Image Credit: Craig Douglas, Michigan State University
Show students where digested small organic molecules go in the body.
Use slides 13 and 14 to explain that the small organic molecules enter the hyphae and travel throughout all parts of a fungus’ body.
Show slide 15. Have students move their pennies into the hyphae on the Decomposer 11x17 Poster.
Show slide 16. Have students move the pennies from the tree trunk into the mushroom and the pennies from the soil detritus further into the hyphae.

15. Small molecules are taken up by fungal hyphae
Small organic molecules are taken in by hyphae.
Image Credit: Craig Douglas, Michigan State University
Show students where digested small organic molecules go in the body.
Use slides 13 and 14 to explain that the small organic molecules enter the hyphae and travel throughout all parts of a fungus’ body.
Show slide 15. Have students move their pennies into the hyphae on the Decomposer 11x17 Poster.
Show slide 16. Have students move the pennies from the tree trunk into the mushroom and the pennies from the soil detritus further into the hyphae.
Small organic molecules are taken in by hyphae.

16. Small organic molecules are transported by fungal hyphae
Move pennies through fungal hyphae to here: the small molecules move to the mushroom
Small organic molecules are transported by fungal hyphae
Move pennies through fungal hyphae to here: the small molecules move through the fungal hyphae
Image Credit: Craig Douglas, Michigan State University
Show students where digested small organic molecules go in the body.
Use slides 13 and 14 to explain that the small organic molecules enter the hyphae and travel throughout all parts of a fungus’ body.
Show slide 15. Have students move their pennies into the hyphae on the Decomposer 11x17 Poster.
Show slide 16. Have students move the pennies from the tree trunk into the mushroom and the pennies from the soil detritus further into the hyphae.

17. Connecting Questions about Processes at Different Scales: Biosynthesis
Unanswered Questions
Macroscopic Scale
How do fungi grow?
Microscopic Scale
How do fungal cells use small organic molecules to grow?
Atomic-Molecular Scale
How do cells make large organic molecules?
Transition students to talk about biosynthesis.
Use slides 17 and 18 in the PPT to transition to biosynthesis.
Tell students that food can be used for growth, which is done through a process called biosynthesis.
Show slides 19 and 20 to introduce the idea that the molecules that make up a fungi’s food are different from the molecules that make up fungi. Explain that once the food molecules are digested into small organic molecules they can be rearranged into different large organic molecules.

18. How do mushrooms’ cells use food to grow?
Materials for growth: Biosynthesis
Food
Digestion
Energy: Cellular respiration
Credit: Craig Douglas, Michigan State University
Transition students to talk about biosynthesis.
Use slides 17 and 18 in the PPT to transition to biosynthesis.
Tell students that food can be used for growth, which is done through a process called biosynthesis.
Show slides 19 and 20 to introduce the idea that the molecules that make up a fungi’s food are different from the molecules that make up fungi. Explain that once the food molecules are digested into small organic molecules they can be rearranged into different large organic molecules.

19. Food in dead organisms is mostly water and large organic molecules
Image Credit: Craig Douglas, Michigan State University
Transition students to talk about biosynthesis.
Use slides 17 and 18 in the PPT to transition to biosynthesis.
Tell students that food can be used for growth, which is done through a process called biosynthesis.
Show slides 19 and 20 to introduce the idea that the molecules that make up a fungi’s food are different from the molecules that make up fungi. Explain that once the food molecules are digested into small organic molecules they can be rearranged into different large organic molecules.
Cellulose
Plant protein
…and many other large organic molecules.

20. Fungi are mostly water and different large organic molecules
Mushroom protein
Starch
…and many other large organic molecules.
Image Credit: Craig Douglas, Michigan State University
Transition students to talk about biosynthesis.
Use slides 17 and 18 in the PPT to transition to biosynthesis.
Tell students that food can be used for growth, which is done through a process called biosynthesis.
Show slides 19 and 20 to introduce the idea that the molecules that make up a fungi’s food are different from the molecules that make up fungi. Explain that once the food molecules are digested into small organic molecules they can be rearranged into different large organic molecules.

21. What happens during biosynthesis?
Chemical change
Image Credit: Craig Douglas, Michigan State University
Discuss the process of biosynthesis.
Use slide 21 in the PPT and explain that during biosynthesis small organic molecules enter the cells but don’t leave.
Explain that in the cells the small organic molecules are combined into large organic molecules.
Show slide 22. Prompt students to exchange their pennies for a nickels to represent the small organic molecules being combined into a large organic molecule on the Decomposer 11 x 17 Poster. Note: biosynthesis occurs in all cells, but here we use a hyphae and the mushroom stem as an example.
Small organic molecules go into cells, but don’t come out. What happens inside the cells?

22. Biosynthesis is the process of small organic molecules becoming large organic molecules in all parts of the fungus.
Change 5 pennies for a nickel: large organic molecules built here
Image Credit: Craig Douglas, Michigan State University
Discuss the process of biosynthesis.
Use slide 21 in the PPT and explain that during biosynthesis small organic molecules enter the cells but don’t leave.
Explain that in the cells the small organic molecules are combined into large organic molecules.
Show slide 22. Prompt students to exchange their pennies for a nickels to represent the small organic molecules being combined into a large organic molecule on the Decomposer 11 x 17 Poster. Note: biosynthesis occurs in all cells, but here we use a hyphae and the mushroom stem as an example.
Change 5 pennies for a nickel: large organic molecules built here

23. During biosynthesis, small organic molecules are built into large organic molecules
GLUCOSE (SUGAR)
Image Credit: Craig Douglas, Michigan State University
Show what happens at the atomic-molecular scale.
Display slide 23 to show students small organic molecules are built into large organic molecules during biosynthesis.
Show students the Digestion and Biosynthesis 11 X 17 Posters to help students visualize the process.
STARCH

24. What happens to carbon atoms and chemical energy in biosynthesis?
Chemical change
Image Credit: Craig Douglas, Michigan State University
Show an animation of the process of biosynthesis.
Display slide to show an animation of what happens to the molecules and chemical energy during biosynthesis.
When watching the slides, ask students what is happening to energy. Listen to see if they notice that chemical potential energy is conserved in the C-C- and C-H bonds through biosynthesis.
Small organic molecules
Large organic molecules (+ water)
Reactants
Products

25. What happens to carbon atoms and chemical energy in biosynthesis?
Chemical change
Image Credit: Craig Douglas, Michigan State University
Show an animation of the process of biosynthesis.
Display slide to show an animation of what happens to the molecules and chemical energy during biosynthesis.
When watching the slides, ask students what is happening to energy. Listen to see if they notice that chemical potential energy is conserved in the C-C- and C-H bonds through biosynthesis.
Carbon atoms stay in organic molecules with high-energy bonds
Small organic molecules
Large molecules (+ water)
Reactants
Products

26. What happens to food small organic molecule that are not used in biosynthesis?
Image Credit: Craig Douglas, Michigan State University
Ask students to consider what happens to small organic molecules not used by the fungi.
Use slide 26 to ask students what happens to small organic molecules not used in biosynthesis.
Show slide 27 and remind students that some of the organic molecules that fungi take are used for cellular respiration.
Show slide 28 to discuss what happens to other small organic molecules. Point out that a percentage stays in the soil as humus.

27. Decomposers use food in two ways
Materials for growth: Biosynthesis
Food
Digestion
Energy: Cellular respiration
Credit: Craig Douglas, Michigan State University
Ask students to consider what happens to small organic molecules not used by the fungi.
Use slide 26 to ask students what happens to small organic molecules not used in biosynthesis.
Show slide 27 and remind students that some of the organic molecules that fungi take are used for cellular respiration.
Show slide 28 to discuss what happens to other small organic molecules. Point out that a percentage stays in the soil as humus.

28. Decomposers don't digest all the large organic molecules in dead organisms.
Ask students to consider what happens to small organic molecules not used by the fungi.
Use slide 26 to ask students what happens to small organic molecules not used in biosynthesis.
Show slide 27 and remind students that some of the organic molecules that fungi take are used for cellular respiration.
Show slide 28 to discuss what happens to other small organic molecules. Point out that a percentage stays in the soil as humus.

29. Where do the atoms in decomposers come from?
Work with a partner to complete the first chart about atoms.
Transition to have students consider the atoms that make up decomposers.
Show slide 29 of the PPT. Pass out 5.1 Tracing the Atoms and Energy in Decomposers Worksheet to each student.
Tell students that now they have considered how molecules move through and are used by fungi they will now consider the atoms that make up decomposers.
Read the top portions of the worksheet with students.
Have students work with a partner to complete the first chart on the worksheet about atoms.

30. Remembering Nutrition Labels
Decomposer cells are made of:
Water: around 60% (H2O)
Large organic molecules: less than 40%
Starch: Made of CHO atoms
Proteins: Made of CHON atoms
(Some other large organic molecules such as DNA, made from CHONP)
Minerals: around 1%
Many kinds of atoms: sodium, calcium, magnesium, etc.
Have students identify where the atoms that make up decomposers come from.
Show slide 30 of the PPT.
Remind students that in Lesson 2 they learned about the molecules that make up cells and the atoms that make up the molecules.
Discuss the answers to the first chart on the worksheet. The atoms in the large organic molecules of fungi all primarily come from food. Water and air are used during cellular respiration.

31. Where does the energy in decomposers come from?
Work with a partner to complete the second chart about energy.
Have students identify where the energy in decomposers come from.
Show slide 31 of the PPT.
Have students complete the second chart on 5.1 Tracing the Atoms and Energy in Decomposers Worksheet on energy with a partner.
Show slide 32. Remind students that chemical energy is in C-C and C-H bonds.
Discuss students’ answers together. Chemical energy is only found in the food that decomposers take in. There is no chemical energy in the water or air decomposers take in.

32. Chemical Energy Chemical energy is stored in C-C and C-H bonds.
Does water have chemical energy?
Does air have chemical energy?
Does food have chemical energy?
Have students identify where the energy in decomposers come from.
Show slide 31 of the PPT.
Have students complete the second chart on 5.1 Tracing the Atoms and Energy in Decomposers Worksheet on energy with a partner.
Show slide 32. Remind students that chemical energy is in C-C and C-H bonds.
Discuss students’ answers together. Chemical energy is only found in the food that decomposers take in. There is no chemical energy in the water or air decomposers take in.

33. Additional Metabolic Pathways
There are many more small organic molecules and ways they can be changed other than the ones in this lesson. Look at the Metabolic Pathways poster to see some of them.
Show students that there are many additional metabolic pathways.
Use slide 33 and the Metabolic Pathways 11 x 17 Poster to show students that there are many more metabolic pathways besides what they learned about in this lesson.
This poster only shows pathways in which small organic molecules are changed into other small organic molecules. There are other pathways that change small organic molecules into large organic molecules.
Organisms are complex; this poster also offers students a glimpse of their complexity.