Note: This lesson is designed to be a follow up of Lesson 1 Form A.
Biomass is an important concept to understand because it is the base of our food supplies, our lumber supplies (which affects building and paper supplies), and our ability to convert it into energy both as a direct fuel (burning biomass) and converting it into biofuels such as ethanol. The amount of biomass a plant can generate directly corresponds to its value as a biofuels crop. While many things can be converted into biofuels such as sugar and corn, non-food sources of biofuels such as switch grass allows for a greater production of fuel without cutting into our food supply chain. Thus, having a plant, such as switch grass, with high biomass productivity, allows for a greater potential of generating more biofuels. This simple study will allow students to see how the growth of a plant can help generate biomass for the potential of renewable fuels.
Biomass is the term that refers to the amount of biological material an organism or group of organisms contains. In other words, it is the “heaviness” of life. Plant biomass is an indicator of photosynthetic activity and growth. When a plant photosynthesizes it creates sugar, which it then uses to grow, reproduce, and store for later use. The amount of sugar that is initially produced is known as the Gross Productivity (or Gross Primary Productivity) of the plant and is directly related to the photosynthetic activity. However, this is generally very hard to measure since the plant constantly is using the sugar for life functions. (Note: Plants use cellular respiration just like animals to break that sugar down to use for life functions). The main way a plant’s productivity is calculated is through its Net Productivity, or what is left over after the plant has used what is needed. (Just like a paycheck after taxes).
A simple way to calculate the Net Productivity of a plant is to cut it down, dry it out, and weigh it. This method is simplistic because it does not include the biomass of the roots in the soil. For a more complex method to include the roots in the biomass study see the Appendix.
Note: If students want to keep a few of their plants to take home, only half of the plants would really be necessary to get an idea of the biomass.
- Drying Pans: Aluminum pans or foil with edges folded up on the sides to make a little pan.
- Electronic scale reading to at least one decimal place.
- Markers for labeling the drying pans.
- Not necessary, but helpful: a drying oven (small enclosed oven for drying scientific samples) or regular oven set on the lowest possible temperature.
- Label the drying pan with the group name.
- Weigh the drying pan on the electronic balance. Record the mass of the pan in the chart below.
- Cut the plants off at their base just above the soil. Make sure there is no soil on the plants. Place them on the drying pan. Mass the fresh cut plants with the pan. Record the mass.
- Place the plants and drying pan on the electronic balance and weigh them. Record the mass of the plants and the pan on the chart below. Calculate the mass of the plants by subtracting the mass of the pan.
- Allow the plants to completely dry out.Place the plants in a drying oven set on low for 24 hours.Place them in a regular oven set at the lowest temperature for 2 – 3 hours. Turn off the oven and let them rest inside the oven over night.On a windowsill for several days to a week.
- Mass the pan and the dried plants and record the mass in the chart below. Calculate the mass of the dried plants by subtracting the mass of the pan. This is the biomass of the plants.
- Calculate the amount of water in the plant.Mass of Fresh cut plant – Mass of dried plant = Mass of water in plant
- Calculate the Water Percentage in the Plant.