Target Grade Level / Age Range

6th grade


5-10 minutes each day for two weeks;


Students will observe how plants increase in mass due to photosynthesis and apply ideas of the conservation of mass.


  • Soybeans – 4 per group
  • Paper towels – 2 per group
  • Spray bottle of water
  • CD case – 1 per group
  • Class copies of “Seedlings in a Jar” from Everyday Life Science Mysteries: Stories for inquiry-based science teaching by Richard Konicek-Moran (can be found starting on page 91
  • Contribution to the History of Photosynthesis: Johann Baptista Van Helmont and John Woodward by CropsReview.Com and Ben G. Bareja
  • Topsy Turvy Soybean Lesson, available at 

Suggested Companion Resources

  • Everyday Life Science Mysteries: Stories for inquiry based science teaching by Richard Konicek-Moran
  • Putting on Mass: Just how do trees grow? by Rachel Hughes and Kirsten Bittle
  • “Where do Trees Get Their Mass From” Veritasium


  • Photosynthesis – The process by which plants, algae, and some bacteria use sunlight, carbon dioxide, and water to make food
  • Cellular Respiration –The process by which cells use oxygen to produce energy from food
  • Conservation of Mass – The Law of Conservation of Mass states that matter can be changed from one form into another, mixtures can be separated or made, and pure substances can be decomposed, but the total amount of mass remains constant.

Interest Approach or Motivator

The students will be placed in groups of 3-5 students. Each group will need four soybean seeds, two paper towels, and a CD case. A spray water bottle will be shared between groups. The students should place the paper towels inside the CD cases and wet them with the spray water bottle. Then, the four soybeans should be placed in opposite corners of the circular inset of the CD case. The case should be closed, and students should label the beans 1-4.  

Background – Agricultural Connections

Most students (and adults) have the misconception that plants get their matter and mass from the soil or water without really giving any thought to the other ingredients which go into a plant, particularly ingredients from the air. A plant receives over 95% of its mass from carbon dioxide in the air through the process of photosynthesis, which can be mind-boggling to students and adults alike.

With photosynthesis plants achieve the means of matter for their growth. VERY basically, some of the sugars produced during photosynthesis are turned into starches, and those starches can then be turned into cellulose which makes up a plants cell structures (especially the cell wall). 

The mass of a field bean is important to farmers because soybeans are paid for by weight per bushel. When soybeans cannot photosynthesize correctly, the bean doesn’t develop mass correctly and therefore, doesn’t weigh as much. Farmers can get docked, or charged money, for having soybeans that are underweight.


  1. Students will take their observations of the growth of the field beans during the 1-2 weeks. The mass of any water used to water the beans will be taken and divided by the number of beans watered. We need to keep track of the water just in case some students say that the material which makes up a plant is from water.
  2. Students will take mass measurements of the beans and the DRIED paper towels (as the paper towels were dry during their first mass measurement). We will take note of how the paper towels mass didn’t change that much and the beans did.
  3. Students will read a modified version of “Seedlings in the Jar,” leaving out the students conclusions of where the mass of the plants in the jar came from. Ask students, “If the bean mass didn’t come from the paper towels in our lab, and the plants mass in the story didn’t come from the soil, where does a plants mass come from?” We will then discuss this question as a class, noting the students’ ideas on the board.
  4. Students will then read a reading as a class about Jan Baptist van Helmont and his experiment with a tree. Van Helmont took the mass of a tree seed and the mass of some soil. He placed the soil in a barrel and planted the seed. He placed a lid on the container with a hole for the tree to grow through, but kept other materials from moving in or out of the container. And, of course, he added water during the 5 year experiment. He then took the mass of the tree and found it to gain about 70 kg, while the mass of the soil only decreased 60 g after he dried it.   He concluded that it was water that made up the matter of the tree (note: this was also a time when many still believed that matter was made of the four element air, earth, water, and fire, which may have helped lead him to his conclusion).
    1. Ask the students, “What are your thoughts about Jan van Helmont’s conclusion?” We will discuss this questions in small groups and then as a class. Some students may insist that Helmont was correct.  
    2. Students will then compare the mass of the water from their CD case soybeans.
  5. We will quickly bring in concepts of the conservation of matter and will guide the student to the idea that water isn’t what makes up the mass of a plant, particularly if the plant is dry (the mass of the bean plants and the mass of the water used from the lab data won’t match).
    1. Ask students, “Besides water, what other ingredients go into a plant during photosynthesis?” We will again hit on the ideas of conservation of mass if a student tries to say the plants are made of sunlight as energy from the sun has no mass (or extremely tiny mass if you follow physics). The only other ingredient left to make up the mass of the field bean plant from the process of photosynthesis is carbon dioxide. Teachers may have to guide students to this answer as they talk in small groups.
  6. Talk with students about why mass matters.
    1. Does it matter how much a plant weighs? Are there any circumstances in which a plant’s weight is important?
    2. If you were farming field beans in the soil rather than a CD case, how would mass impact the farmer’s success?
    3. What might impact the ability of a plant to photosynthesize?
      1. Good student answers may include: too much water causes roots to rot instead of store sugars, hail might destroy leaf surface area and prevent uptake of sunlight, a plant underwater would have no access to oxygen to photosynthesize, a plant in drought conditions will roll it’s leaves to stop cellular respiration, and in the process, stop taking in sunlight, etc.  

Extension Activities

  • Have the students perform the same experiment as the girls from the story “Seedlings in the Jar” outside of the classroom if they have the materials.
  • Have students take measurements of soybeans grown in different years. Without knowing background information about the growing season of the bean, have students predict about the success of the farming year.  



  • James Sleep
  • Kelsey Faivre – IALF 

National Agriculture Literacy Outcomes

  • Describe how biological processes influence and are leveraged in agricultural production and processing (e.g., photosynthesis, fermentation, cell division, heredity/genetics, nitrogen fixation) 

Iowa Core Standards

  • Science
    • MS-PS1-5. Develop and use a model to describe how the total number of atoms does not change in a chemical reaction and thus mass is conserved.
    • MS-LS1-6. Construct a scientific explanation based on evidence for the role of photosynthesis in the cycling of matter and flow of energy into and out of organisms.

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