Question: All large trees start as little seeds. What provided most of the mass that allow trees to grow so large? I think most it came from the nutrients in the soil that are taken up by the roots. I think most of it came from the molecules in the air that came in through the stomata. I think most of it came from the water taken up directly by the plants roots. 1. Which of these opinions do you agree with? Explain. 2. Almost all of a plant's mass consists of H2O and organic molecules. How does a plant get or make these molecules? Major Type of Molecule in Plants H2O Organic molecules (e.g. cellulose, starch, glucose) How does the plant get or make these molecules? During photosynthesis, light energy is converted to chemical energy stored as ATP and then in the bonds of sugar molecules. The atoms in these sugar molecules come from CO2 and H2O, as shown in the following chemical equation which summarizes the process of photosynthesis. sunlight 6 CO2 + 6 H2O 6 O2 + C6H12O6 3. Use the information in this chemical equation to complete the following table. Atom in sugar molecule produced by photosynthesis C Where did this atom come from? (which reactant?) H O
4a. In 1642-47, Helmont carried out a classic experiment to evaluate where a plant s mass came from. He grew a willow tree in a pot and added only water during the five-year experiment. He recorded the weight of the tree and the weight of the soil in the pot at the beginning and end of his experiment. Complete the following table to show the change in weight of the tree and the dried soil. (Note: 16 ounces = 1 pound) Weight of Tree Weight of Dried Soil 1642 5 pounds 200 pounds 1647 169 pounds, 3 ounces 199 pounds, 14 ounces Change in Weight 4b.Helmont concluded from his experiment that, for all plants, almost all of their weight comes from water. Based on Helmont s experiment and results, is this conclusion justified? Explain why or why not. If Helmont's conclusion is not valid, state a more valid conclusion based on the results of his experiment. 5a. In order to further explore this question a former ACP student set up an experiment in which plants were grown in a contained water system for two weeks. This system allowed the student to measure how much water was added to the plant every day and how much water evaporated from the plant every day. In addition, the student measured the mass of the plant before and after the experiment. Their results are shown below Added Evaporated water used by the plant Before 1000 ml 987 ml 20g 200g After Mass gained by the plant 5b. Does this experiment support or refute Helmont s claim that plant mass comes from water? Use the data to justify your answer.
6a. Another enterprising ACP student decided to take this question one step further. Plants were grown in a closed system that allowed the student to control the amount of carbon dioxide provided to each plant. The mass of each plant was determined before and after the experiment. The results are shown below. Change = final measurement initial measurement Concentration of % Change = Change/initial measurement Mass Before Mass After Change % Change CO2 0% 20 15 1% 20 18 3% 20 21 5% 20 26 10% 20 35 6b. Based on the data above, what is the relationship between the amount of carbon dioxide provided to a plant and the amount of mass it accumulates? Explain your answer. Hypothesis Support and Refutation: Reread the hypotheses in the cartoon above. Pick one hypothesis to support and two to refute. Make sure to use evidence from the experiments and to justify your use of the evidence to either support or refute the hypothesis. Hypothesis 1: The mass of a plant comes from the soil. Hypothesis 2: The mass of the plant comes from the air. Hypothesis 3: The mass of the plant comes from the water it takes up through its roots.
Plant Growth Puzzle 1. An experimenter grew three batches of seeds, each weighing 1.5 g, in three different conditions, as shown in the table below. For each condition, predict whether the seeds will germinate and grow into plants. (Think about how seeds normally start growing underground.) Growing Condition Will plants grow? Predicted Biomass at 10 days (question 2) Light, no water yes no Light, water No light, water yes no yes no 2. After 10 days the seeds and/or plants from each condition were dried in an oven overnight (to remove all the water). Then, plant biomass was measured in grams. For each condition, predict the amount of biomass. (Seeds have very little water, so each batch of seeds originally had ~1.5 g biomass.) 3. Two processes that affect the biomass of a plant are photosynthesis and cellular respiration. Complete the following concept map to show the interconnections between photosynthesis and cellular respiration. - All of the white arrows mean that something is produced or used. - Each curved rectangle represents a type of organism. Label each box with plant" or animal and heterotroph or autotroph. - All other shapes represent products or reactants. Label each shape. Photosynthesis Light Energy Word Bank: ATP Autotroph CO2 Glucose Plant Heterotrophs Cellular Respiration O2 Animal 4. Which molecule in question 3 can be converted to other organic molecules such as cellulose and starch that become part of the plant s biomass? Notice that the sugars produced by photosynthesis are used for two different purposes: (1) building blocks to synthesize the molecules that make up the plant s biomass (2) input for cellular respiration to produce the ATP needed to provide energy for the plant s biological processes.
5. Which process can result in increased biomass for a plant? Where does the mass come from? 6. Which process can result in decreased biomass for a plant? How does the mass exit the plant? 7. A seed contains a lot of starch and oil to provide energy in order for the seed to germinate when a plant first begins to grow. When a seed begins growing underground in the dark, the plant cannot (cellular respiration/photosynthesis), because there is no light. Therefore, a plant growing in the dark will only (cellular respiration /photosynthesis) and the plant will (gain/lose) biomass. 8. Think again about the expected change in biomass for each batch of seeds in the three different growing conditions. Based on your answers to questions 3-7, predict the biomass after 10 days in each growing condition. (Remember that each batch of seeds had ~1.5 g of biomass.) Growing Condition Predicted Biomass Reason for Decrease, Increase or No Change in Biomass Observed Biomass (question 9) Light, no water Light, No light, 9. Your teacher will give you the answers for the observed biomass of each germinated (or not germinated) plant. Enter the observed results in the table above. Use your understanding of cellular respiration and photosynthesis to explain the observed decrease, increase or no change in biomass.