During the first lesson, students hopefully put forward a range of ideas on what could be done in order to create proper conditions for living in space including growing plants or other organisms there for producing oxygen and absorbing carbon dioxide. The purpose of the following lesson is to encourage students to think about “how” do we know “what” we actually know about photosynthesis.
In other words, when students claim something related to photosynthesis, it is the right moment to ask “how do you (or we) know that?”. This emphasis will nicely link activity 1 to activity 2 where discoveries as a result of human endeavour are revealed by introducing historical figures and experiments that contributed to the body of knowledge scientists have on the processes of photosynthesis.
Activity 2. 1 Writing activity
Groups (3-5 persons) are asked to use the Internet or library resources to research the experiments conducted by one of these scientists related to photosynthesis:
Jan van Helmont (1643)
After careful measurements of a plant’s water intake and mass increase, van Helmont concludes that trees gain most of their mass from water.
Joseph Priestly (1771)
Using a bell jar, a candle, and a plant, Priestly finds that the plant releases a substance that keeps the candle burning – a substance that we know is oxygen.
Jan Ingenhousz (1779)
Ingenhousz finds that aquatic plants produce oxygen bubbles in the light but not in the dark. He concludes that plants need sunlight to produce oxygen.
Julius Robert Mayer (1845)
Mayer proposes that plants convert light energy into chemical energy
Samuel Ruben and Martin Kamen (1941)
Ruben and Kamen use isotopes to determine that the oxygen liberated in photosynthesis comes from water.
Melvin Calvin (1948)
Calvin traces the chemical path that carbon follows to form glycose. These light-independent reactions are known as the Calvin cycle.
Rudolph Marcus (1992)
Marcus wins the Nobel prize in chemistry for describing the process by which electrons are transferred from one molecule to another in the electron transport chain.
Based on their investigation, students write a summary (e.g. in the form of a poster) describing how the scientist contributed to the modern understanding of photosynthesis.
An alternative version of this stage may be that groups produce a PowerPoint presentation or even a video clip about the explored scientist and his discovery. In the last case the activity takes much more time (2-3 lessons + home work) as it involves both the process of setting and videotaping of a role-play.
Activity 2. 2 Compiling a flowchart
In this phase students put together the results of their group work, e.g. students present their posters on the classroom wall. Depending on the time sequence, groups introduce the ideas (~5 min.) that contributed to the development of photosynthesis-related knowledge.