Day 1: Photosynthesis
To prepare, cut out shapes of aluminum foil and tape them to various part of a house plant’s leaves. Place the plant in the sun for several days.
To introduce the lesson, ask “What do plants and animals need to survive?” Show students a plant such as Coleus or Elodea and a picture of a fish (or a real fish). Make a chart on board, such as the one below, and have students help you fill it in.
Shelter (suitable environmental conditions)
Ask, “In a small fish bowl that contains a fish and a plant, what will happen over time?”
Students should mention the exchange of oxygen and carbon dioxide between the fish and the plant. Tell students that plants and animals on Earth are interdependent.
Tell students that this lesson is all about the energy exchange between plants and animals in the processes of photosynthesis and cell respiration, and that the lesson will focus on photosynthesis. Explain that the simplest way to explain photosynthesis is that it is the process of making energy from light. Have students point out where on the house plant photosynthesis takes place. (in the chloroplasts inside leaf cells)
Have students recall what they know about the structure and function of chloroplasts from Lesson 1. Show students the images in Internal Structure of a Chloroplast (S-B-7-2_Internal Structure.doc) and point out the stroma, thylakoids, and grana. If you have a microscope with a projector, this is a good time to show students actual magnified leaf cells and point out the chloroplasts.
Fill a beaker or plastic cup about halfway with sodium bicarbonate solution (a source of carbon dioxide). Place a sprig of an Elodea plant into a large test tube with the cut stem at the bottom. Fill the test tube with sodium bicarbonate solution. Holding your thumb over the mouth of the test tube, turn it upside down and lower it carefully into the beaker. Make sure there is no air trapped in the tube. Have students observe the setup carefully and describe what they see. Place the cup in bright sunlight. Leave it for at least 20 minutes, and then show it to students again. They should see bubbles of gas around the Elodea leaves. Remind students that photosynthesis produces sugars and oxygen, and because sugars are not gases, this must be oxygen gas. Oxygen is a waste product of photosynthesis because it is released from the plant into the environment.
Hand out copies of Photosynthesis (The Light and Calvin Reactions) (S-B-7-2_Light and Calvin Reactions and KEY.doc). Write the equation for photosynthesis on the board and have students write it on the worksheet, and have them write the equation in sentence form.
6CO2 + 6H2O C6H12O6 + 6O2
Tell students that scientists describe photosynthesis in two parts: the light-dependent reaction and the light-independent reaction, or Calvin cycle. Show students the diagram of the reactions using Reactions of Photosynthesis (S-B-7-2_Reactions of Photosynthesis.doc). Describe the light-dependent reaction and the Calvin cycle using the diagram, and have students take notes in the chart on the worksheet. Be sure to explain the roles of ATP (chemical compound that living things use to store and release energy) and NADP+ (carrier molecule that transfers high-energy electrons from chlorophyll to chemical reactions in other parts of the cell) in the reactions.
Exit Ticket: Describe the role of ATP in the process of photosynthesis.
Day 2: Cell Respiration
Mini-Lesson: Have students take notes as you explain cell respiration. Explain that overall, photosynthesis and cell respiration are opposite processes. Remind students that photosynthesis converts sunlight energy into glucose and other high-energy sugars, which in turn serve as food for other organisms. In aerobic (oxidative) respiration, both plants and animals convert the glucose back into energy for growth and other life processes. The chemical equation for respiration shows that glucose is combined with oxygen to release energy.
C6H12O6 + 6O2 6CO2 + 6H2O + energy
Respiration is the breaking down of glucose for energy to grow and carry out other life processes (metabolism). It is important to emphasize that respiration takes place in the cells of both plants and animals. Have students recall what they know about the structure and function of the mitochondria from Lesson 1.
Explain that there are three major cycles in cell respiration: glycolysis, the citric acid (or Krebs) cycle, and the electron transport chain.
- Glycolysis: glucose is broken down into a simpler compound known as pyruvate.
- Krebs cycle: Pyruvate is converted to a variety of energy-rich compounds, such as ATP and NADH (nicotinamide adenine dinucleotide).
- Electron transport chain: The energy-rich compounds are converted to ATP.
For guided practice, show students the Overview of Cell Respiration (S-B-7-2_Overview of Cell Respiration.doc). Have them use the diagram to answer these questions:
- What molecule is broken down in cell respiration? (glucose)
- What molecule is a product of all three stages? (ATP)
- What is its function? (Store energy for cell processes)
- What is also produced during glycolysis and the Krebs cycle? (CO2)
Have students copy the diagram in their notes and label each stage, as well as the reactants and products.
For independent practice, have students complete the Cell Respiration worksheet (S-B-7-2_Cell Respiration Worksheet and KEY.doc).
Days 3–4: Comparing Photosynthesis and Cell Respiration
To prepare, obtain Elodea and aquatic organisms. These can be ordered through a biological supply company, such as Carolina Biological Supply, or obtained at a local aquarium store. See related resources below.
CAUTION: Make sure that students wear safety goggles during the entire lab. Have them follow the procedure to set up the lab, and then fill in the Design table. They should leave the experimental setup for at least an hour; overnight is preferable.
Have students work in groups of 3–4 to design an experiment on the relationship between photosynthesis and respiration, using the questions shown on the Photosynthesis and Respiration Lab worksheet (S-B-7-2_Photosynthesis and Respiration Lab and KEY.doc). First, they should develop a hypothesis for each question and fill in the Develop a Hypothesis table on the worksheet.
Explain that in order to test their hypotheses, they can use an acid-base indicator called Bromothymol blue solution. Show them the Bromothymol Blue Color Change and have them copy the sentences from the resource into their notes, filling in the blanks (S-B-7-2_Bromothymol Blue Color Change.doc). Bromothymol blue shows the presence of carbon dioxide by turning yellow, because carbon dioxide creates an acidic solution (i.e., carbonic acid). In low levels of carbon dioxide, the solution will appear blue.
Acid (CO2 present)
Describe the experimental procedure from the lab handout as you demonstrate it step by step. Have students follow the procedure for the four test tubes and fill out the Design Table on the lab handout.
While students are waiting, have them complete the independent practice: Students work individually to complete the Comparison of Photosynthesis and Cell Respiration chart (S-B-7-2_Comparison and KEY.doc) and the Photosynthesis and Respiration: Plant Diagram (S-B-7-2_Plant Diagram.doc).Have students observe the changes in each of the test tubes, and write their observations and conclusions. Have them clean up all lab materials. Discuss their conclusions as a whole class. Ask students:
- “Why did the control stay the same color?
- What happened in the test tube with the snail and the Elodea?
- What would happen if all the test tubes were kept in a dark place instead?”
Students should be able to explain that the snail releases CO2 when it carries out respiration; this turns the solution yellow because it is acidic. The Elodea releases O2 when it carries out photosynthesis; this turns the solution blue because it is basic. The solution in the test tube with the snail and Elodea does not change because the processes of photosynthesis and respiration balance each other out.
Conclude the lesson with a discussion of the overall energy transfer that occurs between photosynthesis and respiration.
- Students who might need an opportunity for additional learning can creatively illustrate the light-dependent and Calvin cycle reactions in their notes.
- Students who might need an opportunity for additional learning can write each of the reactants and products of photosynthesis and cell respiration on separate index cards. Have them arrange the index cards to show the process of photosynthesis, and then rearrange them to show the process of cell respiration, to reinforce that the processes are complementary.
- Students who may be going beyond the standards can research the distinction between the light dependent reaction and the light independent reaction of photosynthesis and write the chemical equation for each reaction.
- Students who may be going beyond the standards can view the animations of photosynthesis and cellular respiration by clicking those links at Virtual Cell Animation Collection available at http://vcell.ndsu.edu/animations/. Create a flowchart for the steps of one of the processes.
- Design an experiment similar to the Photosynthesis and Cell Respiration lab, in which all of the test tubes are placed in a dark environment, including hypotheses and predictions.