UNIT 2 Chapter 3. Elodea and Photosynthesis. The Origins of Life. Learning Outcomes: Chapter 3 Lab/Activity #2. Introduction: Safety Issues:

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1 The Origins of Life UNIT 2 Chapter 3 Name: Section: Date: Chapter 3 Lab/Activity #2 Elodea and Photosynthesis Introduction: Photosynthetic organisms (cyanobacteria) first evolved about 3.5 billion years ago and are the oldest known fossils on Earth. Cyanobacteria live in water, can manufacture their own food, and are one of the most important groups of bacteria on Earth. The cyanobacteria have been important in shaping the course of evolution and ecological change throughout Earth s history. Cyanobacteria took in atmospheric carbon dioxide, water and sunlight and converted it into sugar (glucose) and released the waste product oxygen. Photosynthesis reduced the amount of carbon dioxide in the atmosphere, as oxygen was continually being released. For roughly a billion years, oxygen released by cyanobacteria did not build up in the atmosphere. It was used up by two sources: oceans and rocks. Oxygen dissolved in the oceans and oxidized (rusted) the exposed iron and other minerals, as seen in banded rock formations around the world. Approximately two billion years ago, the reservoirs of oxidizable rock became saturated and thus allowing the buildup of free oxygen in the air. As oxygen moved into the early atmosphere, ultraviolet radiation from the sun split the oxygen molecules (O2), which then recombined, producing the Earth s ozone layer (O 3 ). This, in turn, reduced the amount of incoming ultraviolet radiation striking the Earth. The impact for life on Earth was enormous. With reduced amounts of ultraviolet radiation, organisms moved into shallow water and, ultimately, onto the land. Materials: Elodea stem (up to 10 cm 4 inches). Store Elodea in oxygenated water, use as soon as possible after purchase. Distilled water Baking soda (sodium bicarbonate powder) Test tube rack or metal stand Large test tube Lamp ( watt) Single-edged razor blade Tape Timer or clock Metric ruler Learning Outcomes: After completing this lab activity and studying Chapter 3, The Origins of Life, you should be able to: 1. Construct a simple apparatus to measure the rate of photosynthesis. 2. Observe the process of photosynthesis by watching oxygen bubbling from Elodea plants. 3. Learn that photosynthesis uses carbon dioxide and produces oxygen. 4. Manipulate conditions of an experiment. 5. Record, graph and analyze data collected. 6. Explain photosynthesis and why it is important. 7. Explain why oxygen levels have increased dramatically over the course of the Earth s history. Safety Issues: 1. Glass Hazard: Test tubes need to be handled with care. 2. Heat Hazard: lamp bulb can get very hot. Do not allow drops of water near the hot light bulbs. The bulbs may explode. 3. Chemical Hazard: Do not ingest chemicals; wash hands when finished. Theories and Origins of Life Lab/Activity 2 3-7

2 UNIT 2 Chapter 3 The Origins of Life Vocabulary: Autotroph self-nourishing ; refers to plants. Cyanobacteria another name for bluegreen algae. Glucose a six carbon sugar. Photosynthesis putting together with light ; the process of using carbon dioxide, water and sunlight to make glucose. Respiration the process of converting sugar into energy. Procedure: 1. Research Question(s): This lab activity will allow you to see the release of oxygen gas in the freshwater plant, Elodea. You will manipulate the conditions for photosynthesis by changing amounts of available light and carbon dioxide. Can changes in carbon dioxide or light influence the rate of photosynthesis? 2. Literature Review: This purpose of this lab activity is to observe photosynthesis in action using the freshwater plant Elodea. Photosynthesis converts carbon dioxide, water and energy (in the form of light) to sugar, water and oxygen. The chemical equation looks like this: 6 CO H 2 O C 6 H 12 O H 2 O + 6 O 2 carbon dioxide water vapor light sugar water oxygen gas Instruction(s) for Teacher: It is essential to maintain the Elodea in well-lit aquaria or similar arrangement. Adding two to three grams of baking soda for each liter of water used will aid in oxygen generation. Alternative Lab Arrangement Large beakers with several sprigs of Elodea can be placed in an inverted water-filled graduated cylinder. Oxygen levels can be read from the graduated cylinder in place of counting bubbles. Elodea stem in test tube. 3. Hypothesis: Based on the research question(s) and the literature review write your hypothesis/prediction(s) below. Answers vary. Students should include a statement regarding the rate of photosynthesis of Elodea such as: 1. The rate of photosynthesis of Elodea, as measured by the amount of oxygen gas given off, is not affected by light. 2. The rate of photosynthesis of Elodea, as measured by the amount of oxygen gas given off, is not affected by carbon dioxide levels. 4. Activity: Station Set-up: 1. Obtain an Elodea stem. Carefully cut away several leaves from the cut end of the stem. Approximately 5 mm (1.5 in) from the cut end, slice the stem at an angle. Lightly crush this end with your fingers. 2. Place the stem in a test tube, partially filled with water, cut end up. Fill test tube to near the top with water. 3. Place the test tube in a rack or affix it to a metal stand. Running the Activity: 1. Place a lamp 5 cm (2 in) from the test tube. 2. Wait for the first signs of bubbles to begin the activity. If no bubbles, cut and gently crush the stem again. 3-8 The Foundation of Life in the Ocean

3 The Origins of Life UNIT 2 Chapter 3 3. Once bubbles start to appear, record the number of bubbles that appear over a three-minute interval. Repeat recording bubbles for three minutes at least one more time. Average your numbers. 4. Move the lamp back 5 cm, 10 cm, 15 cm and 25 cm (2 in, 4 in, 6 in, and 10 in) or as determined by your teacher. Wait one minute and record the number of bubbles that appear over a three minute interval for each light adjustment. Repeat recording bubbles for three minutes at least one more time at each location. Average your numbers. 5. Add a pinch of baking soda to the test tube. Move the lamp back to the 5 cm (2 in) position. Wait one minute and record the number of bubbles that appear over a three-minute interval. Repeat recording bubbles for an additional three-minutes. Average your numbers. 6. Move the lamp back 5 cm, 10 cm, 15 cm and 25 cm (2 in, 4 in, 6 in, and 10 in) or as determined by your teacher. Wait one minute and record the number of bubbles that appear over a three-minute interval at each location. Repeat recording bubbles for three minutes at least one more time at each location. Average your numbers. Instruction(s) for Teacher: You may want students to focus on one variable (light or carbon dioxide) and report findings to others. Data Collection: Elodea Stem in Fresh Water Distance from Light Source Number of Bubbles in 3 Minutes 5 cm (2 in) Number of bubbles will vary 30 5 cm (2 in) 20 Average at 5 cm (2 in) cm (4 in) Number of bubbles decreases with distance 10 cm (4 in) 16 Average at 10 cm (4 in) cm (6 in) cm (6 in) 11 Average at 15 cm (6 in) cm (10 inches) cm (10 in) 9 Average at 25 cm (10 in) 8 Observation statement: What did you observe? Oxygen gas bubbles form on the ends of the Elodea sprig and are released. Light levels influence rate of oxygen production. Theories and Origins of Life Lab/Activity 2 3-9

4 UNIT 2 Chapter 3 The Origins of Life Observation statement: What did you observe? Oxygen production of Elodea sprigs Oxygen gas bubbles form on the ends of the Elodea sprig and under varying or changing light and carbon are released. The addition of baking soda influences the rate of dioxide levels influences the number of oxygen bubbles produced by Elodea sprigs. oxygen production. OXYGEN PRODUCTION OF ELODEA SPRIGS UNDER VARYING CONDITIONS Title: 30 Number of Bubbles Freshwater (blue ink) Baking Soda (red ink) Distance from Light Source 5 cm (2 in) 5 cm (2 in) Average at 5 cm (2 in) 10 cm (4 in) 10 cm (4 in) Average at 10 cm (4 in) 15 cm (6 in) 15 cm (6 in) Average at 15 cm (6 in) 25 cm (10 in) 25 cm (10 in) Average at 25 cm (10 in) Elodea Stem in Fresh Water and Baking Soda cm (2 in) 10 cm (4 in) 15 cm (6 in) 25 cm (10 in) Distance from Light Source Number of Bubbles in 3 Minutes Number of bubbles varies. Number of bubbles decreases with distance. Would expect more bubbles with baking soda treatment compared to freshwater treatment. Analysis of Results: Interpret and analyze your results by answering the following question(s). 1. On graphing paper, use your data to construct a bar graph of your control and experimental groups. Be sure to label the graph and give the graph an appropriate title The Foundation of Life in the Ocean

5 The Origins of Life UNIT 2 Chapter 3 2. Why did you move the lamp away from the Elodea sprig? Answers vary, but should indicate that moving the lamp away from the Elodea sprig reduces the light intensity, which should reduce the bubble count. 3. Why did you add baking soda? Answers vary, but should point out that baking soda is a form of carbon dioxide. 4. What is the independent variable for your group? Distance from Elodea. 5. What change do you expect in the control group? Moving the lamp away causes a reduction in photosynthesis rate, as measured by bubble production. 6. What change do you expect in the experimental group? Adding baking soda increases photosynthesis rate, as measured by bubble production. 7. List the biotic and abiotic factors present. Biotic Elodea Abiotic light source, water, baking soda, oxygen, and carbon dioxide. Conclude and Communicate: 1. The research question for this activity: Can changes in carbon dioxide or light influence the rate of photosynthesis? 2. Your hypothesis/prediction(s) for this activity: Hypothesis/prediction(s) should be the same as at the start of the activity. 1. The rate of photosynthesis of Elodea, as measured by the amount of oxygen gas given off, is not affected by light. 2. The rate of photosynthesis of Elodea, as measured by the amount of oxygen gas given off, is not affected by carbon dioxide levels. Theories and Origins of Life Lab/Activity

6 UNIT 2 Chapter 3 The Origins of Life 3. Is your original hypothesis/prediction(s) supported by your data? Why or why not? Hopefully not, the manipulation of variables should influence the measured parameter. 4. Write two new research questions based on what you have learned from this activity: Answers vary. Students should ask questions such as: 1. What happens when the variables are changed from light and carbon dioxide levels to temperature? 2. What affect does water cloudiness (turbidity) have on photosynthesis? 3. Do colors (wavelengths) of light have an influence on photosynthesis? 5. The value and importance of this activity to the study of science: Answers vary. Students should indicate that they have gained knowledge about: 1. Photosynthesis and its use of carbon dioxide to produce oxygen. 2. The manipulation of experimental conditions to test a hypothesis (i.e., factors that could change the rate of photosynthesis). 3. The importance of photosynthesis. 4. Why oxygen levels have increased dramatically over the course of the Earth s history The Foundation of Life in the Ocean